libpayload: honor TSC information under CONFIG_LP_TIMER_RDTSC

When CONFIG_LP_TIMER_RDTSC is enabled honor the TSC information
exported in the coreboot tables as the cpu_khz frequency. That
allows get_cpu_speed() not to be called which currently relies
on the 8254 PIT. As certain x86 platforms allow that device
to be optional or turned off for power saving reasons, allow
a path where get_cpu_speed() is no longer called. Additionally,
this approach also allows the libpayload to not duplicate logic
that already exists in coreboot.

BUG=chrome-os-partner:50214
BRANCH=glados
TEST=Confirmed in payload TSC frequency is honored instead of
     using get_cpu_speed().

Change-Id: Ib8993afdfb49065d43de705d6dbbdb9174b6f2c4
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/13671
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>
Reviewed-by: Andrey Petrov <andrey.petrov@intel.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/payloads/libpayload/libc/coreboot.c b/payloads/libpayload/libc/coreboot.c
index 3e248e19c3..3abd610be2 100644
--- a/payloads/libpayload/libc/coreboot.c
+++ b/payloads/libpayload/libc/coreboot.c
@@ -231,6 +231,19 @@ static void cb_parse_boot_media_params(unsigned char *ptr,
 	info->boot_media_size = bmp->boot_media_size;
 }
 
+#if IS_ENABLED(CONFIG_LP_TIMER_RDTSC)
+static void cb_parse_tsc_info(void *ptr, struct sysinfo_t *info)
+{
+	const struct cb_tsc_info *tsc_info = ptr;
+
+	if (tsc_info->freq_khz == 0)
+		return;
+
+	/* Honor the TSC frequency passed to the payload. */
+	info->cpu_khz = tsc_info->freq_khz;
+}
+#endif
+
 int cb_parse_header(void *addr, int len, struct sysinfo_t *info)
 {
 	struct cb_header *header;
@@ -386,6 +399,11 @@ int cb_parse_header(void *addr, int len, struct sysinfo_t *info)
 		case CB_TAG_BOOT_MEDIA_PARAMS:
 			cb_parse_boot_media_params(ptr, info);
 			break;
+#if IS_ENABLED(CONFIG_LP_TIMER_RDTSC)
+		case CB_TAG_TSC_INFO:
+			cb_parse_tsc_info(ptr, info);
+			break;
+#endif
 		default:
 			cb_parse_arch_specific(rec, info);
 			break;