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x86, hpet: Restrict read back to affected ATI chipsets

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After programming the HPET, we do a readback as a workaround for
ATI/SBx00 chipsets as a synchronization.  Unfortunately this triggers
an erratum in newer ICH chipsets (ICH9+) where reading the comparator
immediately after the write returns the old value.  Furthermore, as
always, I/O reads are bad for performance.

Therefore, restrict the readback to the chipsets that need it, or, for
debugging purposes, when we are running with hpet=verbose.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Venkatesh Pallipadi <venki@google.com>
LKML-Reference: <20100225185348.GA9674@linux-os.sc.intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
This commit is contained in:
Thomas Gleixner
2010-04-13 15:31:36 +02:00
committed by H. Peter Anvin
parent 1d16b0f2f3
commit 30a564be9d
3 changed files with 23 additions and 12 deletions
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29
arch/x86/kernel/hpet.c
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@@ -36,6 +36,7 @@
unsigned long hpet_address;
u8 hpet_blockid; /* OS timer block num */
u8 hpet_msi_disable;
u8 hpet_readback_cmp;
#ifdef CONFIG_PCI_MSI
static unsigned long hpet_num_timers;
@@ -395,19 +396,23 @@ static int hpet_next_event(unsigned long delta,
* at that point and we would wait for the next hpet interrupt
* forever. We found out that reading the CMP register back
* forces the transfer so we can rely on the comparison with
* the counter register below. If the read back from the
* compare register does not match the value we programmed
* then we might have a real hardware problem. We can not do
* much about it here, but at least alert the user/admin with
* a prominent warning.
* An erratum on some chipsets (ICH9,..), results in comparator read
* immediately following a write returning old value. Workaround
* for this is to read this value second time, when first
* read returns old value.
* the counter register below.
*
* That works fine on those ATI chipsets, but on newer Intel
* chipsets (ICH9...) this triggers due to an erratum: Reading
* the comparator immediately following a write is returning
* the old value.
*
* We restrict the read back to the affected ATI chipsets (set
* by quirks) and also run it with hpet=verbose for debugging
* purposes.
*/
if (unlikely((u32)hpet_readl(HPET_Tn_CMP(timer)) != cnt)) {
WARN_ONCE(hpet_readl(HPET_Tn_CMP(timer)) != cnt,
KERN_WARNING "hpet: compare register read back failed.\n");
if (hpet_readback_cmp || hpet_verbose) {
u32 cmp = hpet_readl(HPET_Tn_CMP(timer));
if (cmp != cnt)
printk_once(KERN_WARNING
"hpet: compare register read back failed.\n");
}
return (s32)(hpet_readl(HPET_COUNTER) - cnt) >= 0 ? -ETIME : 0;