Re: [PATCH v5 3/3] drm/msm/dp: retry 3 times if set sink to D0 poweer state failed

[Kuogee Hsieh]

On 9/12/2022 11:37 AM, Dmitry Baryshkov wrote:
> On 12/09/2022 19:23, Kuogee Hsieh wrote:
> > Bring sink out of D3 (power down) mode into D0 (normal operation) mode
> > by setting DP_SET_POWER_D0 bit to DP_SET_POWER dpcd register. This
> > patch will retry 3 times if written to DP_SET_POWER register failed.
>
> Could you please elaborate this change? Can the sink succeed in 
> reading the DP_SET_POWER, but fail writing DP_SET_POWER?

yes, there is possible since it is not only set local sink device but 
also all downstream sink devices to D0 state.

> > Changes in v5:
> > -- split into two patches
> >
> > Signed-off-by: Kuogee Hsieh <quic_khsieh@xxxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/msm/dp/dp_link.c | 13 ++++++++-----
> >   1 file changed, 8 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/dp/dp_link.c 
> > b/drivers/gpu/drm/msm/dp/dp_link.c
> > index 9d5381d..4360728 100644
> > --- a/drivers/gpu/drm/msm/dp/dp_link.c
> > +++ b/drivers/gpu/drm/msm/dp/dp_link.c
> > @@ -50,6 +50,7 @@ static int dp_aux_link_power_up(struct drm_dp_aux 
> > *aux,
> >   {
> >       u8 value;
> >       ssize_t len;
> > +    int i;
> >         if (link->revision < 0x11)
> >           return 0;
> > @@ -61,11 +62,13 @@ static int dp_aux_link_power_up(struct drm_dp_aux 
> > *aux,
> >       value &= ~DP_SET_POWER_MASK;
> >       value |= DP_SET_POWER_D0;
> >   -    len = drm_dp_dpcd_writeb(aux, DP_SET_POWER, value);
> > -    if (len < 0)
> > -        return len;
> > -
> > -    usleep_range(1000, 2000);
> > +    /* retry for 1ms to give the sink time to wake up */
> > +    for (i = 0; i < 3; i++) {
> > +        len = drm_dp_dpcd_writeb(aux, DP_SET_POWER, value);
> > +        usleep_range(1000, 2000);
> > +        if (len == 1)
> > +            break;
> > +    }
> >         return 0;
> >   }