Prev: [GIT Pull] timer fixes for 2.6.35
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From: Thomas Gleixner on 18 May 2010 11:30
Linus,

Please pull the latest timers-for-linus-hpet git tree from:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git timers-for-linus-hpet

Thanks,

tglx

------------------>
Andreas Herrmann (1):
x86, hpet: Add reference to chipset erratum documentation for disable-hpet-msi-quirk

Thomas Gleixner (1):
x86, hpet: Restrict read back to affected ATI chipsets


arch/x86/include/asm/hpet.h | 1 +
arch/x86/kernel/hpet.c | 29 +++++++++++++++++------------
arch/x86/kernel/quirks.c | 8 ++++++++
3 files changed, 26 insertions(+), 12 deletions(-)

diff --git a/arch/x86/include/asm/hpet.h b/arch/x86/include/asm/hpet.h
index 1d5c08a..004e6e2 100644
--- a/arch/x86/include/asm/hpet.h
+++ b/arch/x86/include/asm/hpet.h
@@ -68,6 +68,7 @@ extern unsigned long force_hpet_address;
extern u8 hpet_blockid;
extern int hpet_force_user;
extern u8 hpet_msi_disable;
+extern u8 hpet_readback_cmp;
extern int is_hpet_enabled(void);
extern int hpet_enable(void);
extern void hpet_disable(void);
diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
index 23b4ecd..a198b7c 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 12e9fea..e72d3fc 100644
--- a/arch/x86/kernel/quirks.c
+++ b/arch/x86/kernel/quirks.c
@@ -495,10 +495,18 @@ 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.
+ * See erratum #27 (Misinterpreted MSI Requests May Result in
+ * Corrupted LPC DMA Data) in AMD Publication #46837,
+ * "SB700 Family Product Errata", Rev. 1.0, March 2010.
+ *
+ * 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,
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