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x86: hpet: fix periodic mode programming on AMD 81xx

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(See http://bugzilla.kernel.org/show_bug.cgi?id=12961)

It partially reverts commit c23e253e67
(x86: hpet: stop HPET_COUNTER when programming periodic mode)

HPET on AMD 81xx chipset needs a second write (with HPET_TN_SETVAL
cleared) to T0_CMP register to set the period in periodic mode.

With this patch HPET_COUNTER is still stopped but not reset when HPET
is programmed in periodic mode. This should help to avoid races when
HPET is programmed in periodic mode and fixes a boot time hang that
I've observed on a machine when using 1000HZ.

[ Impact: fix boot time hang on machines with AMD 81xx chipset ]

Reported-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Andreas Herrmann <andreas.herrmann3@amd.com>
Tested-by: Jeff Mahoney <jeffm@suse.com>
LKML-Reference: <20090421180037.GA2763@alberich.amd.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Andreas Herrmann 2009-04-21 20:00:37 +02:00 committed by Ingo Molnar
parent 3568b71d46
commit 7a6f9cbb37
1 changed files with 17 additions and 1 deletions
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18
arch/x86/kernel/hpet.c
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@ -236,6 +236,10 @@ static void hpet_stop_counter(void)
unsigned long cfg = hpet_readl(HPET_CFG);
cfg &= ~HPET_CFG_ENABLE;
hpet_writel(cfg, HPET_CFG);
}
static void hpet_reset_counter(void)
{
hpet_writel(0, HPET_COUNTER);
hpet_writel(0, HPET_COUNTER + 4);
}
@ -250,6 +254,7 @@ static void hpet_start_counter(void)
static void hpet_restart_counter(void)
{
hpet_stop_counter();
hpet_reset_counter();
hpet_start_counter();
}
@ -309,7 +314,7 @@ static int hpet_setup_msi_irq(unsigned int irq);
static void hpet_set_mode(enum clock_event_mode mode,
struct clock_event_device *evt, int timer)
{
unsigned long cfg;
unsigned long cfg, cmp, now;
uint64_t delta;
switch (mode) {
@ -317,12 +322,23 @@ static void hpet_set_mode(enum clock_event_mode mode,
hpet_stop_counter();
delta = ((uint64_t)(NSEC_PER_SEC/HZ)) * evt->mult;
delta >>= evt->shift;
now = hpet_readl(HPET_COUNTER);
cmp = now + (unsigned long) delta;
cfg = hpet_readl(HPET_Tn_CFG(timer));
/* Make sure we use edge triggered interrupts */
cfg &= ~HPET_TN_LEVEL;
cfg |= HPET_TN_ENABLE | HPET_TN_PERIODIC |
HPET_TN_SETVAL | HPET_TN_32BIT;
hpet_writel(cfg, HPET_Tn_CFG(timer));
hpet_writel(cmp, HPET_Tn_CMP(timer));
udelay(1);
/*
* HPET on AMD 81xx needs a second write (with HPET_TN_SETVAL
* cleared) to T0_CMP to set the period. The HPET_TN_SETVAL
* bit is automatically cleared after the first write.
* (See AMD-8111 HyperTransport I/O Hub Data Sheet,
* Publication # 24674)
*/
hpet_writel((unsigned long) delta, HPET_Tn_CMP(timer));
hpet_start_counter();
hpet_print_config();