Greg Kroah-Hartman
2018-Nov-19 16:28 UTC
[PATCH 4.18 104/171] clockevents/drivers/i8253: Add support for PIT shutdown quirk
4.18-stable review patch. If anyone has any objections, please let me know.
------------------
From: Michael Kelley <mikelley at microsoft.com>
commit 35b69a420bfb56b7b74cb635ea903db05e357bec upstream.
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 at microsoft.com>
Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
Cc: "gregkh at linuxfoundation.org" <gregkh at
linuxfoundation.org>
Cc: "devel at linuxdriverproject.org" <devel at
linuxdriverproject.org>
Cc: "daniel.lezcano at linaro.org" <daniel.lezcano at
linaro.org>
Cc: "virtualization at lists.linux-foundation.org" <virtualization
at lists.linux-foundation.org>
Cc: "jgross at suse.com" <jgross at suse.com>
Cc: "akataria at vmware.com" <akataria at vmware.com>
Cc: "olaf at aepfle.de" <olaf at aepfle.de>
Cc: "apw at canonical.com" <apw at canonical.com>
Cc: vkuznets <vkuznets at redhat.com>
Cc: "jasowang at redhat.com" <jasowang at redhat.com>
Cc: "marcelo.cerri at canonical.com" <marcelo.cerri at
canonical.com>
Cc: KY Srinivasan <kys at microsoft.com>
Cc: stable at vger.kernel.org
Link: https://lkml.kernel.org/r/1541303219-11142-2-git-send-email-mikelley at
microsoft.com
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
---
drivers/clocksource/i8253.c | 14 ++++++++++++--
include/linux/i8253.h | 1 +
2 files changed, 13 insertions(+), 2 deletions(-)
--- a/drivers/clocksource/i8253.c
+++ b/drivers/clocksource/i8253.c
@@ -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_eve
raw_spin_lock(&i8253_lock);
outb_p(0x30, PIT_MODE);
- outb_p(0, PIT_CH0);
- outb_p(0, PIT_CH0);
+
+ if (i8253_clear_counter_on_shutdown) {
+ outb_p(0, PIT_CH0);
+ outb_p(0, PIT_CH0);
+ }
raw_spin_unlock(&i8253_lock);
return 0;
--- a/include/linux/i8253.h
+++ b/include/linux/i8253.h
@@ -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);