HPET : Legacy Routing Replacement Enable - 3rd try.

[Om Narasimhan <om.turyx@gmail.com>]

I have incorporated Randy's comments.
CC-ing HPET developers.

Patch here.
Signed-off-by: Om Narasimhan <om.turyx@gmail.com>


 Documentation/hpet.txt              |   56 +++++++++++++++++++++++++++++++++++
 Documentation/kernel-parameters.txt |    9 ++++++
 arch/i386/kernel/acpi/boot.c        |   18 +++++++++++
 arch/i386/kernel/time_hpet.c        |    3 +-
 arch/x86_64/kernel/time.c           |   16 +++++++---
 include/asm-x86_64/hpet.h           |    1 +
 include/linux/acpi.h                |    1 +
 include/linux/hpet.h                |    7 ++++
 8 files changed, 105 insertions(+), 6 deletions(-)

diff --git a/Documentation/hpet.txt b/Documentation/hpet.txt
index b7a3dc3..ca62b69 100644
--- a/Documentation/hpet.txt
+++ b/Documentation/hpet.txt
@@ -298,3 +298,59 @@ members of the hpet_task structure befor
 hpet_control simply vectors to the hpet_ioctl routine and has the same
 commands and respective arguments as the user API.  hpet_unregister
 is used to terminate usage of the HPET timer reserved by hpet_register.
+
+		HPET Legacy Replacement Route option (hpet_lrr)
+
+HPET is capable of replacing the IRQ0 (connected INT0 PIN) routing for
+timer interrupt. The capability register (at offset 0 of HPET
+base address) has a bit specifying if HPET chip is capbale of doing
+this. OS can read the bit either from HW or ACPI table. (HPET ACPI
+description table -> Event Timer block -> bit 15, page 30 of HPET
+spec).  Ideally (I think so!) BIOS should set the ACPI table than letting
+the OS read H/W, which gives the BIOS a way to configure either legacy
+or Legacy replacement modes.
+
+Typically the motherboard has BIOS configured / hardwired IRQ0 to INT0
+(pin of APIC) connection. Linux assumes IRQ0 connected to INT0 unless it is
+supplied using an override parameter in the MPTable. Some NVidia chipsets /
+BIOS initialization code had configured to override IRQ0 -> INT0 connection
+and later a parameter was introduce (acpi_skip_timer_override) to get IRQ0 ->
+INT0 connection right.
+
+But a number of bioses (both phoenix and AMI) are not working as
+expected. (I have an AMI BIOS which sets ACPI table bit 15 to 0 and then
+connect IRQ0 -> INT2 internally, Another bios I have sets the ACPI table bit
+15 to 0, but does not connect IRQ0 -> INT2. Both would result in a hang in
+calibrate_delay() since there would not be any timer interrupts So I have
+provided a command line parameter which overrides
+the BIOS ACPI entry. So, irrespctive of the BIOS' HPET ACPI Descriptor
+table settings, if the parameter hpet_lrr=[0,1] is specified, it takes
+precedence.
+
+* When to use this parameter?
+
+Some latest versions CK-804 (e.g),(Actually the code initializes the
+CK804 in the BIOS), would correctly set the HPET such that there would not
+be any interrupts on INT0. Linux does not handle this situation very well
+because in linux, if HW is LRR capable, it is enabled from the OS. Still the
+timer interrupt handler is setup for IRQ0. Under this situation, you can 
+force the parameter hpet_lrr=1, so that IRQ2 is timer interrupts.
+
+[root@mophia ~]# cat /proc/interrupts | grep 2:
+ 2:        163          0          0          0          1          7
+207     955341    IO-APIC-edge  timer
+
+[root@mophia ~]# uptime
+ 22:52:38 up 15 min,  2 users,  load average: 0.00, 0.01, 0.02
+
+[root@mophia ~]# dmesg | grep -i MP-BIOS
+
+For 15 mts (900 sec), around 95k interrupts on timer looks kinda fine.
+
+* Known Bugs:
+I have tested it only with Nvidia CK-804. There seem to be some kind of timing
+issue between enabling the HPET with LRR set and start of tinerrupts. As a
+result of which, calibrate_delay() hangs because there are no interrupts. If
+you run into such a case, pass lpj=<bogomips * 500> as a work around. i.e, if
+your bogomips is 5000, pass lpj=2500000
+
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index dd00fd5..7916ff5 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -366,6 +366,15 @@ and is between 256 and 4096 characters. 
 	hpet=		[IA-32,HPET] option to disable HPET and use PIT.
 			Format: disable
 
+	hpet_lrr=	[IA32,X86_64,HPET] Option to enable/disable the HPET
+			Legacy replacement route. Please read Documentation/
+			hpet.txt for more info.
+			Format : {"0" | "1"}
+			0 -> Disables Legacy Route Replacement. (Default)
+			1 -> Enables LRR. Please consult your BIOS
+			documentation before doing this.
+			
+
 	cm206=		[HW,CD]
 			Format: { auto | [<io>,][<irq>] }
 
diff --git a/arch/i386/kernel/acpi/boot.c b/arch/i386/kernel/acpi/boot.c
index ab974ff..2c5a798 100644
--- a/arch/i386/kernel/acpi/boot.c
+++ b/arch/i386/kernel/acpi/boot.c
@@ -82,6 +82,17 @@ EXPORT_SYMBOL(acpi_strict);
 acpi_interrupt_flags acpi_sci_flags __initdata;
 int acpi_sci_override_gsi __initdata;
 int acpi_skip_timer_override __initdata;
+/* HPET Legacy routing replacement option passed through ACPI Table */
+int acpi_hpet_lrr;
+/* cmdline opt. for faulty bioses not setting ACPI HPET entry right */
+int hpet_lrr_force;
+
+static int hpet_lrr_setup (char *str)
+{
+	get_option(&str, &hpet_lrr_force);
+	return 1;
+}
+__setup ("hpet_lrr=", hpet_lrr_setup);
 
 #ifdef CONFIG_X86_LOCAL_APIC
 static u64 acpi_lapic_addr __initdata = APIC_DEFAULT_PHYS_BASE;
@@ -669,6 +680,13 @@ #define HPET_RESOURCE_NAME_SIZE 9
 			 "HPET %u", hpet_tbl->number);
 		hpet_res->end = (1 * 1024) - 1;
 	}
+	acpi_hpet_lrr = (hpet_tbl->id & ACPI_HPET_LRR_CAP) ? 1 : 0;
+	/* Print a message about the bios HPET ACPI Desc Table passed.
+	 * LRR bit should not be set in the table unless IRQ0->INT2 is
+	 * connected. But BIOS may be faulty ...
+	 */
+	printk(KERN_INFO PREFIX "HPET id: %#x. ACPI LRR bit %s SET\n",
+			hpet_tbl->id, acpi_hpet_lrr ? "": "NOT");
 
 #ifdef	CONFIG_X86_64
 	vxtime.hpet_address = hpet_tbl->addr.addrl |
diff --git a/arch/i386/kernel/time_hpet.c b/arch/i386/kernel/time_hpet.c
index 1a2a979..01b2f67 100644
--- a/arch/i386/kernel/time_hpet.c
+++ b/arch/i386/kernel/time_hpet.c
@@ -94,7 +94,8 @@ static int hpet_timer_stop_set_go(unsign
  	 * Go!
  	 */
 	cfg = hpet_readl(HPET_CFG);
-	if (hpet_use_timer)
+	/* Ideally the following should be &&(acpi_hpet_lrr || hpet_lrr_force) */
+	if (hpet_use_timer && hpet_lrr_force)
 		cfg |= HPET_CFG_LEGACY;
 	cfg |= HPET_CFG_ENABLE;
 	hpet_writel(cfg, HPET_CFG);
diff --git a/arch/x86_64/kernel/time.c b/arch/x86_64/kernel/time.c
index 1ba5a44..0f5d990 100644
--- a/arch/x86_64/kernel/time.c
+++ b/arch/x86_64/kernel/time.c
@@ -46,9 +46,6 @@ #include <asm/apic.h>
 #ifdef CONFIG_CPU_FREQ
 static void cpufreq_delayed_get(void);
 #endif
-extern void i8254_timer_resume(void);
-extern int using_apic_timer;
-
 static char *timename = NULL;
 
 DEFINE_SPINLOCK(rtc_lock);
@@ -783,7 +780,10 @@ static int hpet_timer_stop_set_go(unsign
 		    HPET_TN_32BIT, HPET_T0_CFG);
 		hpet_writel(hpet_tick, HPET_T0_CMP); /* next interrupt */
 		hpet_writel(hpet_tick, HPET_T0_CMP); /* period */
-		cfg |= HPET_CFG_LEGACY;
+		/* Ideal value (acpi_hpet_lrr || hpet_lrr_force) */
+		if (hpet_lrr_force)
+			cfg |= HPET_CFG_LEGACY;
+
 	}
 /*
  * Go!
@@ -887,6 +887,7 @@ time_cpu_notifier(struct notifier_block 
 
 void __init time_init(void)
 {
+	int timer_irq = 0;
 	if (nohpet)
 		vxtime.hpet_address = 0;
 
@@ -906,6 +907,10 @@ void __init time_init(void)
 	  	tick_nsec = TICK_NSEC_HPET;
 		cpu_khz = hpet_calibrate_tsc();
 		timename = "HPET";
+		/* Ideal value is (acpi_hpet_lrr || hpet_lrr_force) */
+		if (hpet_lrr_force)
+			timer_irq = HPET_TIMER_LRR_IRQ;
+
 #ifdef CONFIG_X86_PM_TIMER
 	} else if (pmtmr_ioport && !vxtime.hpet_address) {
 		vxtime_hz = PM_TIMER_FREQUENCY;
@@ -924,7 +929,8 @@ #endif
 	vxtime.tsc_quot = (USEC_PER_MSEC << US_SCALE) / cpu_khz;
 	vxtime.last_tsc = get_cycles_sync();
 	set_cyc2ns_scale(cpu_khz);
-	setup_irq(0, &irq0);
+	printk(KERN_WARNING PREFIX "Registering Timer IRQ = %d\n", timer_irq);
+	setup_irq(timer_irq, &irq0);
 	hotcpu_notifier(time_cpu_notifier, 0);
 	time_cpu_notifier(NULL, CPU_ONLINE, (void *)(long)smp_processor_id());
 
diff --git a/include/asm-x86_64/hpet.h b/include/asm-x86_64/hpet.h
index b390984..2d18b39 100644
--- a/include/asm-x86_64/hpet.h
+++ b/include/asm-x86_64/hpet.h
@@ -37,6 +37,7 @@ #define HPET_CFG_ENABLE	0x001
 #define HPET_CFG_LEGACY	0x002
 #define	HPET_LEGACY_8254	2
 #define	HPET_LEGACY_RTC		8
+#define	HPET_TIMER_LRR_IRQ	2
 
 #define HPET_TN_LEVEL		0x0002
 #define HPET_TN_ENABLE		0x0004
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index 2b0c955..62dab08 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -220,6 +220,7 @@ enum acpi_interrupt_id {
 };
 
 #define	ACPI_SPACE_MEM		0
+#define	ACPI_HPET_LRR_CAP	0x8000
 
 struct acpi_gen_regaddr {
 	u8  space_id;
diff --git a/include/linux/hpet.h b/include/linux/hpet.h
index 707f7cb..6c31473 100644
--- a/include/linux/hpet.h
+++ b/include/linux/hpet.h
@@ -119,6 +119,13 @@ int hpet_register(struct hpet_task *, in
 int hpet_unregister(struct hpet_task *);
 int hpet_control(struct hpet_task *, unsigned int, unsigned long);
 
+
+/* these are used by time.c */
+extern void i8254_timer_resume(void);
+extern int using_apic_timer;
+extern int acpi_hpet_lrr;
+extern int hpet_lrr_force;
+
 #endif /* __KERNEL__ */
 
 struct hpet_info {