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What: /sys/firmware/acpi/interrupts/
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Contact: Len Brown <lenb@kernel.org>
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All ACPI interrupts are handled via a single IRQ,
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the System Control Interrupt (SCI), which appears
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as "acpi" in /proc/interrupts.
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However, one of the main functions of ACPI is to make
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the platform understand random hardware without
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special driver support. So while the SCI handles a few
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well known (fixed feature) interrupts sources, such
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as the power button, it can also handle a variable
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number of a "General Purpose Events" (GPE).
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A GPE vectors to a specified handler in AML, which
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can do a anything the BIOS writer wants from
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OS context. GPE 0x12, for example, would vector
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to a level or edge handler called _L12 or _E12.
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The handler may do its business and return.
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Or the handler may send send a Notify event
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to a Linux device driver registered on an ACPI device,
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such as a battery, or a processor.
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To figure out where all the SCI's are coming from,
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/sys/firmware/acpi/interrupts contains a file listing
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every possible source, and the count of how many
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times it has triggered.
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$ cd /sys/firmware/acpi/interrupts
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sci - The number of times the ACPI SCI
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has been called and claimed an interrupt.
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sci_not - The number of times the ACPI SCI
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has been called and NOT claimed an interrupt.
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gpe_all - count of SCI caused by GPEs.
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gpeXX - count for individual GPE source
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ff_gbl_lock - Global Lock
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ff_pwr_btn - Power Button
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ff_rt_clk - Real Time Clock
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ff_slp_btn - Sleep Button
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error - an interrupt that can't be accounted for above.
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invalid: it's either a GPE or a Fixed Event that
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doesn't have an event handler.
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disable: the GPE/Fixed Event is valid but disabled.
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enable: the GPE/Fixed Event is valid and enabled.
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Root has permission to clear any of these counters. Eg.
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All counters can be cleared by clearing the total "sci":
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None of these counters has an effect on the function
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of the system, they are simply statistics.
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Besides this, user can also write specific strings to these files
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to enable/disable/clear ACPI interrupts in user space, which can be
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used to debug some ACPI interrupt storm issues.
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Note that only writting to VALID GPE/Fixed Event is allowed,
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i.e. user can only change the status of runtime GPE and
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Fixed Event with event handler installed.
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Let's take power button fixed event for example, please kill acpid
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and other user space applications so that the machine won't shutdown
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when pressing the power button.
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# press the power button for 3 times;
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# echo disable > ff_pwr_btn
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# press the power button for 3 times;
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# echo enable > ff_pwr_btn
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* this is because the status bit is set even if the enable bit is cleared,
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* and it triggers an ACPI fixed event when the enable bit is set again
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# press the power button for 3 times;
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# echo disable > ff_pwr_btn
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# press the power button for 3 times;
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# echo clear > ff_pwr_btn /* clear the status bit */
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# echo disable > ff_pwr_btn