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
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@ -20,6 +20,13 @@
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DEFINE_RAW_SPINLOCK(i8253_lock);
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EXPORT_SYMBOL(i8253_lock);
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/*
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* Handle PIT quirk in pit_shutdown() where zeroing the counter register
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* restarts the PIT, negating the shutdown. On platforms with the quirk,
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* platform specific code can set this to false.
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*/
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bool i8253_clear_counter_on_shutdown __ro_after_init = true;
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#ifdef CONFIG_CLKSRC_I8253
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/*
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* Since the PIT overflows every tick, its not very useful
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@ -109,8 +116,11 @@ static int pit_shutdown(struct clock_event_device *evt)
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raw_spin_lock(&i8253_lock);
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outb_p(0x30, PIT_MODE);
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outb_p(0, PIT_CH0);
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outb_p(0, PIT_CH0);
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if (i8253_clear_counter_on_shutdown) {
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outb_p(0, PIT_CH0);
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outb_p(0, PIT_CH0);
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}
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raw_spin_unlock(&i8253_lock);
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return 0;
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@ -21,6 +21,7 @@
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#define PIT_LATCH ((PIT_TICK_RATE + HZ/2) / HZ)
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extern raw_spinlock_t i8253_lock;
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extern bool i8253_clear_counter_on_shutdown;
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extern struct clock_event_device i8253_clockevent;
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extern void clockevent_i8253_init(bool oneshot);
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