According to the data sheet, writing the MODE register should stop the
counter (and thus the interrupts). This appears to work on real hardware,
at least modern Intel and AMD systems. It should also work on Hyper-V.
However, on some buggy virtual machines the mode change doesn't have any
effect until the counter is subsequently loaded (or perhaps when the IRQ
next fires).
So, set MODE 0 and then load the counter, to ensure that those buggy VMs
do the right thing and the interrupts stop. And then write MODE 0 *again*
to stop the counter on compliant implementations too.
Apparently, Hyper-V keeps firing the IRQ *repeatedly* even in mode zero
when it should only happen once, but the second MODE write stops that too.
Userspace test program (mostly written by tglx):
=====
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdint.h>
#include <sys/io.h>
static __always_inline void __out##bwl(type value, uint16_t port) \
{ \
asm volatile("out" #bwl " %" #bw "0, %w1" \
: : "a"(value), "Nd"(port)); \
} \
\
static __always_inline type __in##bwl(uint16_t port) \
{ \
type value; \
asm volatile("in" #bwl " %w1, %" #bw "0" \
: "=a"(value) : "Nd"(port)); \
return value; \
}
BUILDIO(b, b, uint8_t)
#define inb __inb
#define outb __outb
#define PIT_MODE 0x43
#define PIT_CH0 0x40
#define PIT_CH2 0x42
static int is8254;
static void dump_pit(void)
{
if (is8254) {
// Latch and output counter and status
outb(0xC2, PIT_MODE);
printf("%02x %02x %02x\n", inb(PIT_CH0), inb(PIT_CH0), inb(PIT_CH0));
} else {
// Latch and output counter
outb(0x0, PIT_MODE);
printf("%02x %02x\n", inb(PIT_CH0), inb(PIT_CH0));
}
}
int main(int argc, char* argv[])
{
int nr_counts = 2;
if (argc > 1)
nr_counts = atoi(argv[1]);
if (argc > 2)
is8254 = 1;
if (ioperm(0x40, 4, 1) != 0)
return 1;
dump_pit();
printf("Set oneshot\n");
outb(0x38, PIT_MODE);
outb(0x00, PIT_CH0);
outb(0x0F, PIT_CH0);
dump_pit();
usleep(1000);
dump_pit();
printf("Set periodic\n");
outb(0x34, PIT_MODE);
outb(0x00, PIT_CH0);
outb(0x0F, PIT_CH0);
dump_pit();
usleep(1000);
dump_pit();
dump_pit();
usleep(100000);
dump_pit();
usleep(100000);
dump_pit();
printf("Set stop (%d counter writes)\n", nr_counts);
outb(0x30, PIT_MODE);
while (nr_counts--)
outb(0xFF, PIT_CH0);
dump_pit();
usleep(100000);
dump_pit();
usleep(100000);
dump_pit();
printf("Set MODE 0\n");
outb(0x30, PIT_MODE);
dump_pit();
usleep(100000);
dump_pit();
usleep(100000);
dump_pit();
return 0;
}
=====
Suggested-by: Sean Christopherson <seanjc@google.com>
Co-developed-by: Li RongQing <lirongqing@baidu.com>
Signed-off-by: Li RongQing <lirongqing@baidu.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Michael Kelley <mhkelley@outlook.com>
Link: https://lore.kernel.org/all/20240802135555.564941-2-dwmw2@infradead.org
Leaving the PIT interrupt running can cause noticeable steal time for
virtual guests. The VMM generally has a timer which toggles the IRQ input
to the PIC and I/O APIC, which takes CPU time away from the guest. Even
on real hardware, running the counter may use power needlessly (albeit
not much).
Make sure it's turned off if it isn't going to be used.
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Michael Kelley <mhkelley@outlook.com>
Link: https://lore.kernel.org/all/20240802135555.564941-1-dwmw2@infradead.org
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
Remove the hysterical outb/inb_pit defines and use outb_p/inb_p in the
code.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: John Stultz <john.stultz@linaro.org>
Link: http://lkml.kernel.org/r/20110609130622.348437125@linutronix.de
arm, mips and x86 implement i8253 based clockevents. All the same code
copied. Create a common implementation in drivers/clocksource/i8253.c.
About time to rename drivers/clocksource/ to something else.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: John Stultz <john.stultz@linaro.org>
Link: http://lkml.kernel.org/r/20110609130621.921710458@linutronix.de
x86 defines PIT_LATCH as LATCH which in <linux/timex.h> is defined as
((CLOCK_TICK_RATE + HZ/2) / HZ) and <asm/timex.h> again defines
CLOCK_TICK_RATE as PIT_TICK_RATE.
MIPS defines PIT_LATCH as LATCH which in <linux/timex.h> is defined as
((CLOCK_TICK_RATE + HZ/2) / HZ) and <asm/timex.h> again defines
CLOCK_TICK_RATE as 1193182.
ARM defines PITCH_LATCH as ((PIT_TICK_RATE + HZ / 2) / HZ) - and that's
the sanest thing and equivalent to above definitions so use that as the
new definition in <linux/i8253.h>.
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-mips@linux-mips.org
Link: http://lkml.kernel.org/r/20110601180610.832810002@duck.linux-mips.net
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
