[U-Boot] [PATCH 4/6] x86: tsc: Try hardware calibration first

Christian Gmeiner
2018-08-14T06:54:23Z

Am Fr., 10. Aug. 2018 um 11:40 Uhr schrieb Bin Meng <bmeng.cn@gmail.com>:
>
> 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>
> ---
>
> drivers/timer/tsc_timer.c | 27 ++++++++++++++++-----------
> 1 file changed, 16 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/timer/tsc_timer.c b/drivers/timer/tsc_timer.c
> index 747f190..6473de2 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)

Where gets uc_priv->clock_rate set to something? DM should set zero-out
the whole uc_priv thing when bind/probe - or?

> + 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;
> }
> --
> 2.7.4
>
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--
greets
--
Christian Gmeiner, MSc