---

yaml
---
r: 210759
b: refs/heads/master
c: 54ff7e5
h: refs/heads/master
i:
  210757: accf7ab
  210755: c897bd6
  210751: 2559dd5
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 08c2b394b98786ebb067e2a54d08f1f6f0d247da
+refs/heads/master: 54ff7e595d763d894104d421b103a89f7becf47c

trunk/arch/x86/include/asm/hpet.h

@@ -68,7 +68,6 @@ 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);

trunk/arch/x86/kernel/early-quirks.c

@@ -18,7 +18,6 @@
 #include <asm/apic.h>
 #include <asm/iommu.h>
 #include <asm/gart.h>
-#include <asm/hpet.h>
 
 static void __init fix_hypertransport_config(int num, int slot, int func)
 {
@@ -192,21 +191,6 @@ static void __init ati_bugs_contd(int num, int slot, int func)
 }
 #endif
 
-/*
- * 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.
- *
- * We do this on all SMBUS incarnations for now until we have more
- * information about the affected chipsets.
- */
-static void __init ati_hpet_bugs(int num, int slot, int func)
-{
-#ifdef CONFIG_HPET_TIMER
-	hpet_readback_cmp = 1;
-#endif
-}
-
 #define QFLAG_APPLY_ONCE 	0x1
 #define QFLAG_APPLIED		0x2
 #define QFLAG_DONE		(QFLAG_APPLY_ONCE|QFLAG_APPLIED)
@@ -236,8 +220,6 @@ static struct chipset early_qrk[] __initdata = {
 	  PCI_CLASS_SERIAL_SMBUS, PCI_ANY_ID, 0, ati_bugs },
 	{ PCI_VENDOR_ID_ATI, PCI_DEVICE_ID_ATI_SBX00_SMBUS,
 	  PCI_CLASS_SERIAL_SMBUS, PCI_ANY_ID, 0, ati_bugs_contd },
-	{ PCI_VENDOR_ID_ATI, PCI_ANY_ID,
-	  PCI_CLASS_SERIAL_SMBUS, PCI_ANY_ID, 0, ati_hpet_bugs },
 	{}
 };
 

trunk/arch/x86/kernel/hpet.c

@@ -35,7 +35,6 @@
 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;
@@ -395,23 +394,27 @@ 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.
+	 * 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.
 	 *
-	 * 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.
+	 * 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.
 	 *
-	 * We restrict the read back to the affected ATI chipsets (set
-	 * by quirks) and also run it with hpet=verbose for debugging
-	 * purposes.
+	 * In fact the write to the comparator register is delayed up
+	 * to two HPET cycles so the workaround we tried to restrict
+	 * the readback to those known to be borked ATI chipsets
+	 * failed miserably. So we give up on optimizations forever
+	 * and penalize all HPET incarnations unconditionally.
 	 */
-	if (hpet_readback_cmp || hpet_verbose) {
-		u32 cmp = hpet_readl(HPET_Tn_CMP(timer));
-
-		if (cmp != cnt)
+	if (unlikely((u32)hpet_readl(HPET_Tn_CMP(timer)) != cnt)) {
+		if (hpet_readl(HPET_Tn_CMP(timer)) != cnt)
 			printk_once(KERN_WARNING
-			    "hpet: compare register read back failed.\n");
+				"hpet: compare register read back failed.\n");
 	}
 
 	return (s32)(hpet_readl(HPET_COUNTER) - cnt) >= 0 ? -ETIME : 0;