[PATCH] i386: fix hpet for systems that don't support legacy replacement

Currently the i386 HPET code assumes the entire HPET implementation from
the spec is present. This breaks on boxes that do not implement the
optional legacy timer replacement functionality portion of the spec.

This patch, which is very similar to my x86-64 patch for the same issue,
fixes the problem allowing i386 systems that cannot use the HPET for the
timer interrupt and RTC to still use the HPET as a time source. I've
tested this patch on a system systems without HPET, with HPET but without
legacy timer replacement, as well as HPET with legacy timer replacement.

Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/i386/kernel/time.c

···
 	set_normalized_timespec(&wall_to_monotonic,
 		-xtime.tv_sec, -xtime.tv_nsec);
 
-	if (hpet_enable() >= 0) {
+	if ((hpet_enable() >= 0) && hpet_use_timer) {
 		printk("Using HPET for base-timer\n");
 	}
 

arch/i386/kernel/time_hpet.c

···
 static unsigned long hpet_period;	/* fsecs / HPET clock */
 unsigned long hpet_tick;		/* hpet clks count per tick */
 unsigned long hpet_address;		/* hpet memory map physical address */
+int hpet_use_timer;
 
 static int use_hpet; 		/* can be used for runtime check of hpet */
 static int boot_hpet_disable; 	/* boottime override for HPET timer */
···
 	hpet_writel(0, HPET_COUNTER);
 	hpet_writel(0, HPET_COUNTER + 4);
 
-	/*
-	 * Set up timer 0, as periodic with first interrupt to happen at
-	 * hpet_tick, and period also hpet_tick.
-	 */
-	cfg = hpet_readl(HPET_T0_CFG);
-	cfg |= HPET_TN_ENABLE | HPET_TN_PERIODIC |
-	       HPET_TN_SETVAL | HPET_TN_32BIT;
-	hpet_writel(cfg, HPET_T0_CFG);
+	if (hpet_use_timer) {
+		/*
+		 * Set up timer 0, as periodic with first interrupt to happen at
+		 * hpet_tick, and period also hpet_tick.
+		 */
+		cfg = hpet_readl(HPET_T0_CFG);
+		cfg |= HPET_TN_ENABLE | HPET_TN_PERIODIC |
+		       HPET_TN_SETVAL | HPET_TN_32BIT;
+		hpet_writel(cfg, HPET_T0_CFG);
 
-	/*
-	 * The first write after writing TN_SETVAL to the config register sets
-	 * the counter value, the second write sets the threshold.
-	 */
-	hpet_writel(tick, HPET_T0_CMP);
-	hpet_writel(tick, HPET_T0_CMP);
-
+		/*
+		 * The first write after writing TN_SETVAL to the config register sets
+		 * the counter value, the second write sets the threshold.
+		 */
+		hpet_writel(tick, HPET_T0_CMP);
+		hpet_writel(tick, HPET_T0_CMP);
+	}
 	/*
  	 * Go!
  	 */
 	cfg = hpet_readl(HPET_CFG);
-	cfg |= HPET_CFG_ENABLE | HPET_CFG_LEGACY;
+	if (hpet_use_timer)
+		cfg |= HPET_CFG_LEGACY;
+	cfg |= HPET_CFG_ENABLE;
 	hpet_writel(cfg, HPET_CFG);
 
 	return 0;
···
 	 * However, we can do with one timer otherwise using the
 	 * the single HPET timer for system time.
 	 */
-	if (
 #ifdef CONFIG_HPET_EMULATE_RTC
-		!(id & HPET_ID_NUMBER) ||
-#endif
-	    !(id & HPET_ID_LEGSUP))
+	if (!(id & HPET_ID_NUMBER))
 		return -1;
+#endif
+
 
 	hpet_period = hpet_readl(HPET_PERIOD);
 	if ((hpet_period < HPET_MIN_PERIOD) || (hpet_period > HPET_MAX_PERIOD))
···
 
 	if (hpet_tick_rem > (hpet_period >> 1))
 		hpet_tick++; /* rounding the result */
+
+	hpet_use_timer = id & HPET_ID_LEGSUP;
 
 	if (hpet_timer_stop_set_go(hpet_tick))
 		return -1;
···
 #endif
 
 #ifdef CONFIG_X86_LOCAL_APIC
-	wait_timer_tick = wait_hpet_tick;
+	if (hpet_use_timer)
+		wait_timer_tick = wait_hpet_tick;
 #endif
 	return 0;
 }

arch/i386/kernel/timers/timer_hpet.c

···
 
 	eax = hpet_readl(HPET_COUNTER);
 	eax -= hpet_last;	/* hpet delta */
-
+	eax = min(hpet_tick, eax);
 	/*
          * Time offset = (hpet delta) * ( usecs per HPET clock )
 	 *             = (hpet delta) * ( usecs per tick / HPET clocks per tick)
···
 	last_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
 	rdtsc(last_tsc_low, last_tsc_high);
 
-	offset = hpet_readl(HPET_T0_CMP) - hpet_tick;
-	if (unlikely(((offset - hpet_last) > hpet_tick) && (hpet_last != 0))) {
-		int lost_ticks = (offset - hpet_last) / hpet_tick;
+	if (hpet_use_timer)
+		offset = hpet_readl(HPET_T0_CMP) - hpet_tick;
+	else
+		offset = hpet_readl(HPET_COUNTER);
+	if (unlikely(((offset - hpet_last) >= (2*hpet_tick)) && (hpet_last != 0))) {
+		int lost_ticks = ((offset - hpet_last) / hpet_tick) - 1;
 		jiffies_64 += lost_ticks;
 	}
 	hpet_last = offset;

arch/i386/kernel/timers/timer_tsc.c

···
 	if (cpu_has_tsc) {
 		unsigned long tsc_quotient;
 #ifdef CONFIG_HPET_TIMER
-		if (is_hpet_enabled()){
+		if (is_hpet_enabled() && hpet_use_timer) {
 			unsigned long result, remain;
 			printk("Using TSC for gettimeofday\n");
 			tsc_quotient = calibrate_tsc_hpet(NULL);

include/asm-i386/hpet.h

···
 
 extern unsigned long hpet_tick;  	/* hpet clks count per tick */
 extern unsigned long hpet_address;	/* hpet memory map physical address */
+extern int hpet_use_timer;
 
 extern int hpet_rtc_timer_init(void);
 extern int hpet_enable(void);