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* Generic OPP Interface
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* Copyright (C) 2009-2010 Texas Instruments Incorporated.
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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#include <linux/kernel.h>
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#include <linux/errno.h>
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#include <linux/err.h>
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#include <linux/init.h>
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#include <linux/slab.h>
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#include <linux/cpufreq.h>
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#include <linux/list.h>
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#include <linux/rculist.h>
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#include <linux/rcupdate.h>
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#include <linux/opp.h>
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* Internal data structure organization with the OPP layer library is as
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* |- device 1 (represents voltage domain 1)
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* | |- opp 1 (availability, freq, voltage)
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* |- device 2 (represents the next voltage domain)
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* `- device m (represents mth voltage domain)
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* device 1, 2.. are represented by dev_opp structure while each opp
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* is represented by the opp structure.
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* struct opp - Generic OPP description structure
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* @node: opp list node. The nodes are maintained throughout the lifetime
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* of boot. It is expected only an optimal set of OPPs are
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* added to the library by the SoC framework.
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* RCU usage: opp list is traversed with RCU locks. node
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* modification is possible realtime, hence the modifications
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* are protected by the dev_opp_list_lock for integrity.
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* IMPORTANT: the opp nodes should be maintained in increasing
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* @available: true/false - marks if this OPP as available or not
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* @rate: Frequency in hertz
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* @u_volt: Nominal voltage in microvolts corresponding to this OPP
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* @dev_opp: points back to the device_opp struct this opp belongs to
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* This structure stores the OPP information for a given device.
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struct list_head node;
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struct device_opp *dev_opp;
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* struct device_opp - Device opp structure
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* @node: list node - contains the devices with OPPs that
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* have been registered. Nodes once added are not modified in this
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* RCU usage: nodes are not modified in the list of device_opp,
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* however addition is possible and is secured by dev_opp_list_lock
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* @dev: device pointer
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* @head: notifier head to notify the OPP availability changes.
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* @opp_list: list of opps
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* This is an internal data structure maintaining the link to opps attached to
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* a device. This structure is not meant to be shared to users as it is
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* meant for book keeping and private to OPP library
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struct list_head node;
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struct srcu_notifier_head head;
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struct list_head opp_list;
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* The root of the list of all devices. All device_opp structures branch off
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* from here, with each device_opp containing the list of opp it supports in
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* various states of availability.
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static LIST_HEAD(dev_opp_list);
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/* Lock to allow exclusive modification to the device and opp lists */
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static DEFINE_MUTEX(dev_opp_list_lock);
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* find_device_opp() - find device_opp struct using device pointer
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* @dev: device pointer used to lookup device OPPs
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* Search list of device OPPs for one containing matching device. Does a RCU
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* reader operation to grab the pointer needed.
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* Returns pointer to 'struct device_opp' if found, otherwise -ENODEV or
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* -EINVAL based on type of error.
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* Locking: This function must be called under rcu_read_lock(). device_opp
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* is a RCU protected pointer. This means that device_opp is valid as long
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* as we are under RCU lock.
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static struct device_opp *find_device_opp(struct device *dev)
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struct device_opp *tmp_dev_opp, *dev_opp = ERR_PTR(-ENODEV);
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if (unlikely(IS_ERR_OR_NULL(dev))) {
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pr_err("%s: Invalid parameters\n", __func__);
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return ERR_PTR(-EINVAL);
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list_for_each_entry_rcu(tmp_dev_opp, &dev_opp_list, node) {
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if (tmp_dev_opp->dev == dev) {
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dev_opp = tmp_dev_opp;
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* opp_get_voltage() - Gets the voltage corresponding to an available opp
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* @opp: opp for which voltage has to be returned for
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* Return voltage in micro volt corresponding to the opp, else
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* Locking: This function must be called under rcu_read_lock(). opp is a rcu
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* protected pointer. This means that opp which could have been fetched by
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* opp_find_freq_{exact,ceil,floor} functions is valid as long as we are
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* under RCU lock. The pointer returned by the opp_find_freq family must be
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* used in the same section as the usage of this function with the pointer
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* prior to unlocking with rcu_read_unlock() to maintain the integrity of the
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unsigned long opp_get_voltage(struct opp *opp)
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tmp_opp = rcu_dereference(opp);
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if (unlikely(IS_ERR_OR_NULL(tmp_opp)) || !tmp_opp->available)
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pr_err("%s: Invalid parameters\n", __func__);
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* opp_get_freq() - Gets the frequency corresponding to an available opp
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* @opp: opp for which frequency has to be returned for
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* Return frequency in hertz corresponding to the opp, else
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* Locking: This function must be called under rcu_read_lock(). opp is a rcu
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* protected pointer. This means that opp which could have been fetched by
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* opp_find_freq_{exact,ceil,floor} functions is valid as long as we are
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* under RCU lock. The pointer returned by the opp_find_freq family must be
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* used in the same section as the usage of this function with the pointer
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* prior to unlocking with rcu_read_unlock() to maintain the integrity of the
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unsigned long opp_get_freq(struct opp *opp)
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tmp_opp = rcu_dereference(opp);
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if (unlikely(IS_ERR_OR_NULL(tmp_opp)) || !tmp_opp->available)
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pr_err("%s: Invalid parameters\n", __func__);
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* opp_get_opp_count() - Get number of opps available in the opp list
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* @dev: device for which we do this operation
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* This function returns the number of available opps if there are any,
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* else returns 0 if none or the corresponding error value.
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* Locking: This function must be called under rcu_read_lock(). This function
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* internally references two RCU protected structures: device_opp and opp which
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* are safe as long as we are under a common RCU locked section.
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int opp_get_opp_count(struct device *dev)
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struct device_opp *dev_opp;
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struct opp *temp_opp;
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dev_opp = find_device_opp(dev);
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if (IS_ERR(dev_opp)) {
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int r = PTR_ERR(dev_opp);
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dev_err(dev, "%s: device OPP not found (%d)\n", __func__, r);
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list_for_each_entry_rcu(temp_opp, &dev_opp->opp_list, node) {
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if (temp_opp->available)
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* opp_find_freq_exact() - search for an exact frequency
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* @dev: device for which we do this operation
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* @freq: frequency to search for
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* @available: true/false - match for available opp
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* Searches for exact match in the opp list and returns pointer to the matching
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* opp if found, else returns ERR_PTR in case of error and should be handled
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* Note: available is a modifier for the search. if available=true, then the
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* match is for exact matching frequency and is available in the stored OPP
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* table. if false, the match is for exact frequency which is not available.
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* This provides a mechanism to enable an opp which is not available currently
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* or the opposite as well.
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* Locking: This function must be called under rcu_read_lock(). opp is a rcu
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* protected pointer. The reason for the same is that the opp pointer which is
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* returned will remain valid for use with opp_get_{voltage, freq} only while
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* under the locked area. The pointer returned must be used prior to unlocking
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* with rcu_read_unlock() to maintain the integrity of the pointer.
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struct opp *opp_find_freq_exact(struct device *dev, unsigned long freq,
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struct device_opp *dev_opp;
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struct opp *temp_opp, *opp = ERR_PTR(-ENODEV);
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dev_opp = find_device_opp(dev);
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if (IS_ERR(dev_opp)) {
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int r = PTR_ERR(dev_opp);
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dev_err(dev, "%s: device OPP not found (%d)\n", __func__, r);
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list_for_each_entry_rcu(temp_opp, &dev_opp->opp_list, node) {
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if (temp_opp->available == available &&
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temp_opp->rate == freq) {
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* opp_find_freq_ceil() - Search for an rounded ceil freq
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* @dev: device for which we do this operation
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* @freq: Start frequency
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* Search for the matching ceil *available* OPP from a starting freq
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* Returns matching *opp and refreshes *freq accordingly, else returns
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* ERR_PTR in case of error and should be handled using IS_ERR.
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* Locking: This function must be called under rcu_read_lock(). opp is a rcu
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* protected pointer. The reason for the same is that the opp pointer which is
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* returned will remain valid for use with opp_get_{voltage, freq} only while
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* under the locked area. The pointer returned must be used prior to unlocking
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* with rcu_read_unlock() to maintain the integrity of the pointer.
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struct opp *opp_find_freq_ceil(struct device *dev, unsigned long *freq)
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struct device_opp *dev_opp;
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struct opp *temp_opp, *opp = ERR_PTR(-ENODEV);
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dev_err(dev, "%s: Invalid argument freq=%p\n", __func__, freq);
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return ERR_PTR(-EINVAL);
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dev_opp = find_device_opp(dev);
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list_for_each_entry_rcu(temp_opp, &dev_opp->opp_list, node) {
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if (temp_opp->available && temp_opp->rate >= *freq) {
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* opp_find_freq_floor() - Search for a rounded floor freq
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* @dev: device for which we do this operation
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* @freq: Start frequency
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* Search for the matching floor *available* OPP from a starting freq
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* Returns matching *opp and refreshes *freq accordingly, else returns
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* ERR_PTR in case of error and should be handled using IS_ERR.
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* Locking: This function must be called under rcu_read_lock(). opp is a rcu
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* protected pointer. The reason for the same is that the opp pointer which is
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* returned will remain valid for use with opp_get_{voltage, freq} only while
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* under the locked area. The pointer returned must be used prior to unlocking
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* with rcu_read_unlock() to maintain the integrity of the pointer.
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struct opp *opp_find_freq_floor(struct device *dev, unsigned long *freq)
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struct device_opp *dev_opp;
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struct opp *temp_opp, *opp = ERR_PTR(-ENODEV);
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dev_err(dev, "%s: Invalid argument freq=%p\n", __func__, freq);
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return ERR_PTR(-EINVAL);
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dev_opp = find_device_opp(dev);
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list_for_each_entry_rcu(temp_opp, &dev_opp->opp_list, node) {
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if (temp_opp->available) {
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/* go to the next node, before choosing prev */
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if (temp_opp->rate > *freq)
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* opp_add() - Add an OPP table from a table definitions
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* @dev: device for which we do this operation
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* @freq: Frequency in Hz for this OPP
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* @u_volt: Voltage in uVolts for this OPP
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* This function adds an opp definition to the opp list and returns status.
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* The opp is made available by default and it can be controlled using
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* opp_enable/disable functions.
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* Locking: The internal device_opp and opp structures are RCU protected.
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* Hence this function internally uses RCU updater strategy with mutex locks
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* to keep the integrity of the internal data structures. Callers should ensure
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* that this function is *NOT* called under RCU protection or in contexts where
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* mutex cannot be locked.
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int opp_add(struct device *dev, unsigned long freq, unsigned long u_volt)
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struct device_opp *dev_opp = NULL;
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struct opp *opp, *new_opp;
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struct list_head *head;
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/* allocate new OPP node */
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new_opp = kzalloc(sizeof(struct opp), GFP_KERNEL);
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dev_warn(dev, "%s: Unable to create new OPP node\n", __func__);
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/* Hold our list modification lock here */
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mutex_lock(&dev_opp_list_lock);
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/* Check for existing list for 'dev' */
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dev_opp = find_device_opp(dev);
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if (IS_ERR(dev_opp)) {
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* Allocate a new device OPP table. In the infrequent case
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* where a new device is needed to be added, we pay this
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dev_opp = kzalloc(sizeof(struct device_opp), GFP_KERNEL);
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mutex_unlock(&dev_opp_list_lock);
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"%s: Unable to create device OPP structure\n",
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srcu_init_notifier_head(&dev_opp->head);
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INIT_LIST_HEAD(&dev_opp->opp_list);
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/* Secure the device list modification */
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list_add_rcu(&dev_opp->node, &dev_opp_list);
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/* populate the opp table */
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new_opp->dev_opp = dev_opp;
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new_opp->rate = freq;
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new_opp->u_volt = u_volt;
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new_opp->available = true;
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/* Insert new OPP in order of increasing frequency */
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head = &dev_opp->opp_list;
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list_for_each_entry_rcu(opp, &dev_opp->opp_list, node) {
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if (new_opp->rate < opp->rate)
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list_add_rcu(&new_opp->node, head);
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mutex_unlock(&dev_opp_list_lock);
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* Notify the changes in the availability of the operable
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* frequency/voltage list.
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srcu_notifier_call_chain(&dev_opp->head, OPP_EVENT_ADD, new_opp);
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* opp_set_availability() - helper to set the availability of an opp
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* @dev: device for which we do this operation
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* @freq: OPP frequency to modify availability
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* @availability_req: availability status requested for this opp
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* Set the availability of an OPP with an RCU operation, opp_{enable,disable}
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* share a common logic which is isolated here.
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* Returns -EINVAL for bad pointers, -ENOMEM if no memory available for the
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* copy operation, returns 0 if no modifcation was done OR modification was
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* Locking: The internal device_opp and opp structures are RCU protected.
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* Hence this function internally uses RCU updater strategy with mutex locks to
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* keep the integrity of the internal data structures. Callers should ensure
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* that this function is *NOT* called under RCU protection or in contexts where
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* mutex locking or synchronize_rcu() blocking calls cannot be used.
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static int opp_set_availability(struct device *dev, unsigned long freq,
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bool availability_req)
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struct device_opp *tmp_dev_opp, *dev_opp = ERR_PTR(-ENODEV);
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struct opp *new_opp, *tmp_opp, *opp = ERR_PTR(-ENODEV);
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/* keep the node allocated */
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new_opp = kmalloc(sizeof(struct opp), GFP_KERNEL);
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dev_warn(dev, "%s: Unable to create OPP\n", __func__);
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mutex_lock(&dev_opp_list_lock);
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/* Find the device_opp */
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list_for_each_entry(tmp_dev_opp, &dev_opp_list, node) {
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if (dev == tmp_dev_opp->dev) {
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dev_opp = tmp_dev_opp;
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if (IS_ERR(dev_opp)) {
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r = PTR_ERR(dev_opp);
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dev_warn(dev, "%s: Device OPP not found (%d)\n", __func__, r);
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/* Do we have the frequency? */
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list_for_each_entry(tmp_opp, &dev_opp->opp_list, node) {
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if (tmp_opp->rate == freq) {
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/* Is update really needed? */
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if (opp->available == availability_req)
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/* copy the old data over */
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/* plug in new node */
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new_opp->available = availability_req;
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list_replace_rcu(&opp->node, &new_opp->node);
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mutex_unlock(&dev_opp_list_lock);
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/* Notify the change of the OPP availability */
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if (availability_req)
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srcu_notifier_call_chain(&dev_opp->head, OPP_EVENT_ENABLE,
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srcu_notifier_call_chain(&dev_opp->head, OPP_EVENT_DISABLE,
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/* clean up old opp */
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mutex_unlock(&dev_opp_list_lock);
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* opp_enable() - Enable a specific OPP
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* @dev: device for which we do this operation
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* @freq: OPP frequency to enable
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* Enables a provided opp. If the operation is valid, this returns 0, else the
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* corresponding error value. It is meant to be used for users an OPP available
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* after being temporarily made unavailable with opp_disable.
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* Locking: The internal device_opp and opp structures are RCU protected.
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* Hence this function indirectly uses RCU and mutex locks to keep the
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* integrity of the internal data structures. Callers should ensure that
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* this function is *NOT* called under RCU protection or in contexts where
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* mutex locking or synchronize_rcu() blocking calls cannot be used.
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int opp_enable(struct device *dev, unsigned long freq)
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return opp_set_availability(dev, freq, true);
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* opp_disable() - Disable a specific OPP
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* @dev: device for which we do this operation
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* @freq: OPP frequency to disable
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* Disables a provided opp. If the operation is valid, this returns
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* 0, else the corresponding error value. It is meant to be a temporary
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* control by users to make this OPP not available until the circumstances are
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* right to make it available again (with a call to opp_enable).
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* Locking: The internal device_opp and opp structures are RCU protected.
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* Hence this function indirectly uses RCU and mutex locks to keep the
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* integrity of the internal data structures. Callers should ensure that
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* this function is *NOT* called under RCU protection or in contexts where
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* mutex locking or synchronize_rcu() blocking calls cannot be used.
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int opp_disable(struct device *dev, unsigned long freq)
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return opp_set_availability(dev, freq, false);
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#ifdef CONFIG_CPU_FREQ
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* opp_init_cpufreq_table() - create a cpufreq table for a device
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* @dev: device for which we do this operation
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* @table: Cpufreq table returned back to caller
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* Generate a cpufreq table for a provided device- this assumes that the
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* opp list is already initialized and ready for usage.
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* This function allocates required memory for the cpufreq table. It is
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* expected that the caller does the required maintenance such as freeing
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* the table as required.
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* Returns -EINVAL for bad pointers, -ENODEV if the device is not found, -ENOMEM
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* if no memory available for the operation (table is not populated), returns 0
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* if successful and table is populated.
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* WARNING: It is important for the callers to ensure refreshing their copy of
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* the table if any of the mentioned functions have been invoked in the interim.
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* Locking: The internal device_opp and opp structures are RCU protected.
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* To simplify the logic, we pretend we are updater and hold relevant mutex here
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* Callers should ensure that this function is *NOT* called under RCU protection
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* or in contexts where mutex locking cannot be used.
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int opp_init_cpufreq_table(struct device *dev,
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struct cpufreq_frequency_table **table)
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struct device_opp *dev_opp;
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struct cpufreq_frequency_table *freq_table;
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/* Pretend as if I am an updater */
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mutex_lock(&dev_opp_list_lock);
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dev_opp = find_device_opp(dev);
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if (IS_ERR(dev_opp)) {
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int r = PTR_ERR(dev_opp);
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mutex_unlock(&dev_opp_list_lock);
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dev_err(dev, "%s: Device OPP not found (%d)\n", __func__, r);
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freq_table = kzalloc(sizeof(struct cpufreq_frequency_table) *
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(opp_get_opp_count(dev) + 1), GFP_KERNEL);
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mutex_unlock(&dev_opp_list_lock);
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dev_warn(dev, "%s: Unable to allocate frequency table\n",
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list_for_each_entry(opp, &dev_opp->opp_list, node) {
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if (opp->available) {
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freq_table[i].index = i;
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freq_table[i].frequency = opp->rate / 1000;
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mutex_unlock(&dev_opp_list_lock);
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freq_table[i].index = i;
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freq_table[i].frequency = CPUFREQ_TABLE_END;
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*table = &freq_table[0];
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* opp_free_cpufreq_table() - free the cpufreq table
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* @dev: device for which we do this operation
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* @table: table to free
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* Free up the table allocated by opp_init_cpufreq_table
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void opp_free_cpufreq_table(struct device *dev,
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struct cpufreq_frequency_table **table)
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#endif /* CONFIG_CPU_FREQ */
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* opp_get_notifier() - find notifier_head of the device with opp
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* @dev: device pointer used to lookup device OPPs.
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struct srcu_notifier_head *opp_get_notifier(struct device *dev)
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struct device_opp *dev_opp = find_device_opp(dev);
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return ERR_CAST(dev_opp); /* matching type */
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return &dev_opp->head;