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authorBin Meng <bmeng.cn@gmail.com>2018-08-10 02:39:36 -0700
committerBin Meng <bmeng.cn@gmail.com>2018-08-20 13:52:49 +0800
commit165db7c426f1946376c3643fd635afd6b167e3ee (patch)
tree21f553e20ef034c2094be8ac9717aabec5e92cd0 /drivers/timer
parent1cf6825a681c289032f6309d3ac5eab2fd71a703 (diff)
x86: tsc: Try hardware calibration first
At present if TSC frequency is provided in the device tree, it takes precedence over hardware calibration result. This swaps the order to try hardware calibration first and uses device tree as last resort. This can be helpful when a generic dts (eg: coreboot/efi payload) is supposed to work on as many hardware as possible, including emulators like QEMU where TSC hardware calibration sometimes fails. Signed-off-by: Bin Meng <bmeng.cn@gmail.com> Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Diffstat (limited to 'drivers/timer')
-rw-r--r--drivers/timer/tsc_timer.c27
1 files changed, 16 insertions, 11 deletions
diff --git a/drivers/timer/tsc_timer.c b/drivers/timer/tsc_timer.c
index 747f190d38..6473de20f1 100644
--- a/drivers/timer/tsc_timer.c
+++ b/drivers/timer/tsc_timer.c
@@ -341,16 +341,12 @@ static int tsc_timer_get_count(struct udevice *dev, u64 *count)
return 0;
}
-static void tsc_timer_ensure_setup(void)
+static void tsc_timer_ensure_setup(bool stop)
{
if (gd->arch.tsc_base)
return;
gd->arch.tsc_base = rdtsc();
- /*
- * If there is no clock frequency specified in the device tree,
- * calibrate it by ourselves.
- */
if (!gd->arch.clock_rate) {
unsigned long fast_calibrate;
@@ -366,7 +362,10 @@ static void tsc_timer_ensure_setup(void)
if (fast_calibrate)
goto done;
- panic("TSC frequency is ZERO");
+ if (stop)
+ panic("TSC frequency is ZERO");
+ else
+ return;
done:
gd->arch.clock_rate = fast_calibrate * 1000000;
@@ -377,11 +376,17 @@ static int tsc_timer_probe(struct udevice *dev)
{
struct timer_dev_priv *uc_priv = dev_get_uclass_priv(dev);
- if (!uc_priv->clock_rate) {
- tsc_timer_ensure_setup();
- uc_priv->clock_rate = gd->arch.clock_rate;
+ /* Try hardware calibration first */
+ tsc_timer_ensure_setup(false);
+ if (!gd->arch.clock_rate) {
+ /*
+ * Use the clock frequency specified in the
+ * device tree as last resort
+ */
+ if (!uc_priv->clock_rate)
+ panic("TSC frequency is ZERO");
} else {
- gd->arch.tsc_base = rdtsc();
+ uc_priv->clock_rate = gd->arch.clock_rate;
}
return 0;
@@ -394,7 +399,7 @@ unsigned long notrace timer_early_get_rate(void)
* clock rate can only be calibrated via some hardware ways. Specifying
* it in the device tree won't work for the early timer.
*/
- tsc_timer_ensure_setup();
+ tsc_timer_ensure_setup(true);
return gd->arch.clock_rate;
}