Commit 896e97bf authored by Compostella, Jeremy's avatar Compostella, Jeremy Committed by Rafael J. Wysocki
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ACPI: EC: Clear GPE on interrupt handling only 



On multiple devices I work on, we noticed that
/sys/firmware/acpi/interrupts/sci_not is non-zero and keeps increasing
over time.

It turns out that there is a race condition between servicing a GPE
interrupt and handling task driven transactions.

If a GPE interrupt is received at the same time ec_poll() is running,
the advance_transaction() clears the GPE flag and the interrupt is not
serviced as acpi_ev_detect_gpe() relies on the GPE flag to call the
handler. As a result, `sci_not' is increased.

To address this, move the GPE status check and clearing from
advance_transaction() directly into acpi_ec_handle_interrupt(), so the
EC GPE only gets cleared in the interrupt handling path.

Signed-off-by: default avatarJeremy Compostella <jeremy.compostella@intel.com>
[ rjw: Changelog edits ]
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 858fd168

drivers/acpi/ec.c

+16 −15
Original line number Diff line number Diff line
@@ -662,21 +662,6 @@ static void advance_transaction(struct acpi_ec *ec, bool interrupt) 


	ec_dbg_stm("%s (%d)", interrupt ? "IRQ" : "TASK", smp_processor_id());



	/*

	 * Clear GPE_STS upfront to allow subsequent hardware GPE_STS 0->1

	 * changes to always trigger a GPE interrupt.

	 *

	 * GPE STS is a W1C register, which means:

	 *

	 * 1. Software can clear it without worrying about clearing the other

	 *    GPEs' STS bits when the hardware sets them in parallel.

	 *

	 * 2. As long as software can ensure only clearing it when it is set,

	 *    hardware won't set it in parallel.

	 */

	if (ec->gpe >= 0 && acpi_ec_gpe_status_set(ec))

		acpi_clear_gpe(NULL, ec->gpe);



	status = acpi_ec_read_status(ec);



	/*
@@ -1287,6 +1272,22 @@ static void acpi_ec_handle_interrupt(struct acpi_ec *ec) 
	unsigned long flags;



	spin_lock_irqsave(&ec->lock, flags);



	/*

	 * Clear GPE_STS upfront to allow subsequent hardware GPE_STS 0->1

	 * changes to always trigger a GPE interrupt.

	 *

	 * GPE STS is a W1C register, which means:

	 *

	 * 1. Software can clear it without worrying about clearing the other

	 *    GPEs' STS bits when the hardware sets them in parallel.

	 *

	 * 2. As long as software can ensure only clearing it when it is set,

	 *    hardware won't set it in parallel.

	 */

	if (ec->gpe >= 0 && acpi_ec_gpe_status_set(ec))

		acpi_clear_gpe(NULL, ec->gpe);



	advance_transaction(ec, true);

	spin_unlock_irqrestore(&ec->lock, flags);

}