Commit 35b69a42 authored Nov 04, 2018 by Michael Kelley Committed by Thomas Gleixner Nov 04, 2018

clockevents/drivers/i8253: Add support for PIT shutdown quirk



Add support for platforms where pit_shutdown() doesn't work because of a
quirk in the PIT emulation. On these platforms setting the counter register
to zero causes the PIT to start running again, negating the shutdown.

Provide a global variable that controls whether the counter register is
zero'ed, which platform specific code can override.

Signed-off-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>
Cc: "devel@linuxdriverproject.org" <devel@linuxdriverproject.org>
Cc: "daniel.lezcano@linaro.org" <daniel.lezcano@linaro.org>
Cc: "virtualization@lists.linux-foundation.org" <virtualization@lists.linux-foundation.org>
Cc: "jgross@suse.com" <jgross@suse.com>
Cc: "akataria@vmware.com" <akataria@vmware.com>
Cc: "olaf@aepfle.de" <olaf@aepfle.de>
Cc: "apw@canonical.com" <apw@canonical.com>
Cc: vkuznets <vkuznets@redhat.com>
Cc: "jasowang@redhat.com" <jasowang@redhat.com>
Cc: "marcelo.cerri@canonical.com" <marcelo.cerri@canonical.com>
Cc: KY Srinivasan <kys@microsoft.com>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/1541303219-11142-2-git-send-email-mikelley@microsoft.com

parent 71e56028

drivers/clocksource/i8253.c

+12 −2

Original line number	Diff line number	Diff line
		@@ -20,6 +20,13 @@
		DEFINE_RAW_SPINLOCK(i8253_lock);
		EXPORT_SYMBOL(i8253_lock);

		/*
		* Handle PIT quirk in pit_shutdown() where zeroing the counter register
		* restarts the PIT, negating the shutdown. On platforms with the quirk,
		* platform specific code can set this to false.
		*/
		bool i8253_clear_counter_on_shutdown __ro_after_init = true;

		#ifdef CONFIG_CLKSRC_I8253
		/*
		* Since the PIT overflows every tick, its not very useful
		@@ -109,8 +116,11 @@ static int pit_shutdown(struct clock_event_device *evt)
		raw_spin_lock(&i8253_lock);

		outb_p(0x30, PIT_MODE);

		if (i8253_clear_counter_on_shutdown) {
		outb_p(0, PIT_CH0);
		outb_p(0, PIT_CH0);
		}

		raw_spin_unlock(&i8253_lock);
		return 0;

include/linux/i8253.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -21,6 +21,7 @@
		#define PIT_LATCH ((PIT_TICK_RATE + HZ/2) / HZ)

		extern raw_spinlock_t i8253_lock;
		extern bool i8253_clear_counter_on_shutdown;
		extern struct clock_event_device i8253_clockevent;
		extern void clockevent_i8253_init(bool oneshot);

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