[PATCH] drm/bridge: ps8640: Add double reset T4 and T5 to power-on sequence

[Rock Chiu]

How does T4/T5  impact the real case? We talked previously the T4/T5
shouldn't cause user impact.
Do we have testing data from ODM?

Rock Chiu

Hsin-Yi Wang <hsinyi at chromium.org> 於 2022年8月18日 週四 上午10:43寫道：
>
> On Thu, Aug 18, 2022 at 6:54 AM Doug Anderson <dianders at chromium.org> wrote:
> >
> > Hi,
> >
> > On Mon, Aug 15, 2022 at 2:39 AM Hsin-Yi Wang <hsinyi at chromium.org> wrote:
> > >
> > > The double reset power-on sequence is a workaround for the hardware
> > > flaw in some chip that SPI Clock output glitch and cause internal MPU
> > > unable to read firmware correctly. The sequence is suggested in ps8640
> > > application note.
> > >
> > > Signed-off-by: Hsin-Yi Wang <hsinyi at chromium.org>
> > > ---
> > >  drivers/gpu/drm/bridge/parade-ps8640.c | 5 +++++
> > >  1 file changed, 5 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/bridge/parade-ps8640.c b/drivers/gpu/drm/bridge/parade-ps8640.c
> > > index 49107a6cdac18..d7483c13c569b 100644
> > > --- a/drivers/gpu/drm/bridge/parade-ps8640.c
> > > +++ b/drivers/gpu/drm/bridge/parade-ps8640.c
> > > @@ -375,6 +375,11 @@ static int __maybe_unused ps8640_resume(struct device *dev)
> > >         gpiod_set_value(ps_bridge->gpio_reset, 1);
> > >         usleep_range(2000, 2500);
> > >         gpiod_set_value(ps_bridge->gpio_reset, 0);
> > > +       /* Double reset for T4 and T5 */
> > > +       msleep(50);
> > > +       gpiod_set_value(ps_bridge->gpio_reset, 1);
> > > +       msleep(50);
> > > +       gpiod_set_value(ps_bridge->gpio_reset, 0);
> >
> > We really need another 100 ms here? ps8640 is already quite slow at
> > powering itself up and that has a real user impact. Why was it only
> > 2.5 ms for the first reset and 50 ms for the second?
> >
>
> The T4 and T5 are required by Parade. I'm wondering if they can
> shorten the 200ms below:
>
> /*
> * Mystery 200 ms delay for the "MCU to be ready". It's unclear if
> * this is truly necessary since the MCU will already signal that
> * things are "good to go" by signaling HPD on "gpio 9". See
> * _ps8640_wait_hpd_asserted(). For now we'll keep this mystery delay
> * just in case.
> */
> msleep(200);
>
> Does this have to wait 200ms? Can it shorten to 100 due to the
> additional 100ms from T4 and T5?
>
> > -Doug