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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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1
arch/x86/include/asm/hpet.h
View file

@ -68,6 +68,7 @@ extern unsigned long force_hpet_address;
extern u8 hpet_blockid; extern u8 hpet_blockid;
extern int hpet_force_user; extern int hpet_force_user;
extern u8 hpet_msi_disable; extern u8 hpet_msi_disable;
extern u8 hpet_readback_cmp;
extern int is_hpet_enabled(void); extern int is_hpet_enabled(void);
extern int hpet_enable(void); extern int hpet_enable(void);
extern void hpet_disable(void); extern void hpet_disable(void);

29
arch/x86/kernel/hpet.c
View file

@ -36,6 +36,7 @@
unsigned long hpet_address; unsigned long hpet_address;
u8 hpet_blockid; /* OS timer block num */ u8 hpet_blockid; /* OS timer block num */
u8 hpet_msi_disable; u8 hpet_msi_disable;
u8 hpet_readback_cmp;
#ifdef CONFIG_PCI_MSI #ifdef CONFIG_PCI_MSI
static unsigned long hpet_num_timers; 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 * at that point and we would wait for the next hpet interrupt
* forever. We found out that reading the CMP register back * forever. We found out that reading the CMP register back
* forces the transfer so we can rely on the comparison with * forces the transfer so we can rely on the comparison with
* the counter register below. If the read back from the * the counter register below.
* compare register does not match the value we programmed *
* then we might have a real hardware problem. We can not do * That works fine on those ATI chipsets, but on newer Intel
* much about it here, but at least alert the user/admin with * chipsets (ICH9...) this triggers due to an erratum: Reading
* a prominent warning. * the comparator immediately following a write is returning
* An erratum on some chipsets (ICH9,..), results in comparator read * the old value.
* immediately following a write returning old value. Workaround *
* for this is to read this value second time, when first * We restrict the read back to the affected ATI chipsets (set
* read returns old value. * by quirks) and also run it with hpet=verbose for debugging
* purposes.
*/ */
if (unlikely((u32)hpet_readl(HPET_Tn_CMP(timer)) != cnt)) { if (hpet_readback_cmp || hpet_verbose) {
WARN_ONCE(hpet_readl(HPET_Tn_CMP(timer)) != cnt, u32 cmp = hpet_readl(HPET_Tn_CMP(timer));
KERN_WARNING "hpet: compare register read back failed.\n");
if (cmp != cnt)
printk_once(KERN_WARNING
"hpet: compare register read back failed.\n");
} }
return (s32)(hpet_readl(HPET_COUNTER) - cnt) >= 0 ? -ETIME : 0; return (s32)(hpet_readl(HPET_COUNTER) - cnt) >= 0 ? -ETIME : 0;

5
arch/x86/kernel/quirks.c
View file

@ -495,10 +495,15 @@ void force_hpet_resume(void)
/* /*
* HPET MSI on some boards (ATI SB700/SB800) has side effect on * HPET MSI on some boards (ATI SB700/SB800) has side effect on
* floppy DMA. Disable HPET MSI on such platforms. * floppy DMA. Disable HPET MSI on such platforms.
*
* Also force the read back of the CMP register in hpet_next_event()
* to work around the problem that the CMP register write seems to be
* delayed. See hpet_next_event() for details.
*/ */
static void force_disable_hpet_msi(struct pci_dev *unused) static void force_disable_hpet_msi(struct pci_dev *unused)
{ {
hpet_msi_disable = 1; hpet_msi_disable = 1;
hpet_readback_cmp = 1;
} }
DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_ATI, PCI_DEVICE_ID_ATI_SBX00_SMBUS, DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_ATI, PCI_DEVICE_ID_ATI_SBX00_SMBUS,