diff options
| author | Thomas Gleixner <tglx@linutronix.de> | 2010-04-13 15:31:36 +0200 |
|---|---|---|
| committer | H. Peter Anvin <hpa@zytor.com> | 2010-04-28 18:14:29 -0700 |
| commit | 30a564be9d9554c168a654eddc2165869cc0d7bf (patch) | |
| tree | 734de780e0f84a189f66ca3cbf611e6f2bc563e9 /arch/x86/kernel | |
| parent | 1d16b0f2f3edf05f12a9e3960588e0d4854157bb (diff) | |
x86, hpet: Restrict read back to affected ATI chipsets
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>
Diffstat (limited to 'arch/x86/kernel')
| -rw-r--r-- | arch/x86/kernel/hpet.c | 29 | ||||
| -rw-r--r-- | arch/x86/kernel/quirks.c | 5 |
2 files changed, 22 insertions, 12 deletions
diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c index 23b4ecdffa9..a198b7c87a1 100644 --- a/arch/x86/kernel/hpet.c +++ b/arch/x86/kernel/hpet.c @@ -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; diff --git a/arch/x86/kernel/quirks.c b/arch/x86/kernel/quirks.c index 12e9feaa2f7..cd2c336c8d0 100644 --- a/arch/x86/kernel/quirks.c +++ b/arch/x86/kernel/quirks.c @@ -495,10 +495,15 @@ void force_hpet_resume(void) /* * HPET MSI on some boards (ATI SB700/SB800) has side effect on * 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) { hpet_msi_disable = 1; + hpet_readback_cmp = 1; } DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_ATI, PCI_DEVICE_ID_ATI_SBX00_SMBUS, |