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| 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/quirks.c | |
| parent | Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/lrg/voltage-2.6 (diff) | |
| download | linux-dev-30a564be9d9554c168a654eddc2165869cc0d7bf.tar.xz linux-dev-30a564be9d9554c168a654eddc2165869cc0d7bf.zip | |
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/quirks.c')
| -rw-r--r-- | arch/x86/kernel/quirks.c | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/arch/x86/kernel/quirks.c b/arch/x86/kernel/quirks.c index 12e9feaa2f7a..cd2c336c8d09 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, |