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

Christian Gmeiner
2018-08-14T08:35:18Z

Am Di., 14. Aug. 2018 um 09:07 Uhr schrieb Bin Meng <bmeng.cn@gmail.com>:
>
> Hi Christian,
>
> On Tue, Aug 14, 2018 at 2:54 PM, Christian Gmeiner
> <christian.gmeiner@gmail.com> wrote:
> > 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?
> >
>
> uc_priv->clock_rate is set in timer_pre_probe()
>

Ah.. yes - with that new knowledge:

Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>

--
greets
--
Christian Gmeiner, MSc