[Qemu-devel] [PATCH] Probe HPET existence

[Jan Kiszka <jan.kiszka@siemens.com>]

QEMU does not provide a HPET block if it was configured with -no-hpet,
other machines SeaBIOS runs on may lack a HPET as well. Perform basic
checks the ID register for a reasonable vendor ID and a clock period
within the valid range, do not build the HPET table if that fails.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---

This allows to postpone the hpet_fw_cfg vs. ACPI discussion until we
have >1 HPET blocks and/or put them at non-standard addresses.

 src/acpi.c |   14 +++++++++++++-
 1 files changed, 13 insertions(+), 1 deletions(-)

diff --git a/src/acpi.c b/src/acpi.c
index ea7b171..29160f4 100644
--- a/src/acpi.c
+++ b/src/acpi.c
@@ -158,6 +158,9 @@ struct acpi_20_hpet {
 } PACKED;
 #define ACPI_HPET_ADDRESS 0xFED00000UL
 
+#define HPET_ID         0x000
+#define HPET_PERIOD     0x004
+
 /*
  * SRAT (NUMA topology description) table
  */
@@ -464,7 +467,16 @@ build_ssdt(void)
 static void*
 build_hpet(void)
 {
-    struct acpi_20_hpet *hpet = malloc_high(sizeof(*hpet));
+    struct acpi_20_hpet *hpet;
+    const void *hpet_base = (void *)ACPI_HPET_ADDRESS;
+    u32 hpet_vendor = readl(hpet_base + HPET_ID) >> 16;
+    u32 hpet_period = readl(hpet_base + HPET_PERIOD);
+
+    if (hpet_vendor == 0 || hpet_vendor == 0xffff ||
+        hpet_period == 0 || hpet_period > 0x05F5E100)
+        return NULL;
+
+    hpet = malloc_high(sizeof(*hpet));
     if (!hpet) {
         warn_noalloc();
         return NULL;
-- 
1.7.3.4