Patch "clockevents/drivers/i8253: Add support for PIT shutdown quirk" has been added to the 4.19-stable tree

This is a note to let you know that I've just added the patch titled

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

to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
clockevents-drivers-i8253-add-support-for-pit-shutdown-quirk.patch
and it can be found in the queue-4.19 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From 35b69a420bfb56b7b74cb635ea903db05e357bec Mon Sep 17 00:00:00 2001
From: Michael Kelley <[email protected]>
Date: Sun, 4 Nov 2018 03:48:54 +0000
Subject: clockevents/drivers/i8253: Add support for PIT shutdown quirk

From: Michael Kelley <[email protected]>

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.

---
 drivers/clocksource/i8253.c |   14 ++++++++++++--
 include/linux/i8253.h       |    1 +
 2 files changed, 13 insertions(+), 2 deletions(-)

@@ -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;

@@ -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);
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.19/x86-hyper-v-enable-pit-shutdown-quirk.patch queue-4.19/clockevents-drivers-i8253-add-support-for-pit-shutdown-quirk.patch