acpi_hpet: correctly get number of timers/comparators in a timer block

Also, account for a quirk of AMD/ATI HPET which reports number of timers
instead of id of the last timer as manadated by the specification.
Currently this has no effect on functionality but in the future we may
make actual use of the HPET timers, not only of its timecounter.

MFC after:	2 weeks

1 files changed, 18 insertions, 3 deletions

diff --git a/sys/dev/acpica/acpi_hpet.c b/sys/dev/acpica/acpi_hpet.c
index ee346b7..a98a826 100644
--- a/sys/dev/acpica/acpi_hpet.c
+++ b/sys/dev/acpica/acpi_hpet.c
@@ -42,6 +42,9 @@ __FBSDID("$FreeBSD$");
 #include <dev/acpica/acpivar.h>
 #include <dev/acpica/acpi_hpet.h>
 
+#define HPET_VENDID_AMD		0x4353
+#define HPET_VENDID_INTEL	0x8086
+
 ACPI_SERIAL_DECL(hpet, "ACPI HPET support");
 
 static devclass_t acpi_hpet_devclass;
@@ -155,9 +158,10 @@ static int
 acpi_hpet_attach(device_t dev)
 {
 	struct acpi_hpet_softc *sc;
-	int rid;
+	int rid, num_timers;
 	uint32_t val, val2;
 	uintmax_t freq;
+	uint16_t vendor;
 
 	ACPI_FUNCTION_TRACE((char *)(uintptr_t) __func__);
 
@@ -194,10 +198,21 @@ acpi_hpet_attach(device_t dev)
 	freq = (1000000000000000LL + val / 2) / val;
 	if (bootverbose) {
 		val = bus_read_4(sc->mem_res, HPET_CAPABILITIES);
+
+		/*
+		 * ATI/AMD violates IA-PC HPET (High Precision Event Timers)
+		 * Specification and provides an off by one number
+		 * of timers/comparators.
+		 * Additionally, they use unregistered value in VENDOR_ID field.
+		 */
+		num_timers = 1 + ((val & HPET_CAP_NUM_TIM) >> 8);
+		vendor = val >> 16;
+		if (vendor == HPET_VENDID_AMD && num_timers > 0)
+			num_timers--;
 		device_printf(dev,
 		    "vend: 0x%x rev: 0x%x num: %d hz: %jd opts:%s%s\n",
-		    val >> 16, val & HPET_CAP_REV_ID,
-		    (val & HPET_CAP_NUM_TIM) >> 8, freq,
+		    vendor, val & HPET_CAP_REV_ID,
+		    num_timers, freq,
 		    (val & HPET_CAP_LEG_RT) ? " legacy_route" : "",
 		    (val & HPET_CAP_COUNT_SIZE) ? " 64-bit" : "");
 	}