Re: [PATCH 3/3] drm/msm/dp: Handle aux timeouts, nacks, defers

[khsieh]

On 2021-05-24 12:19, Stephen Boyd wrote:
> Quoting khsieh@xxxxxxxxxxxxxx (2021-05-24 09:33:49)
> > On 2021-05-07 14:25, Stephen Boyd wrote:
> > > @@ -367,36 +347,38 @@ static ssize_t dp_aux_transfer(struct drm_dp_aux
> > > *dp_aux,
> > >       }
> > >
> > >       ret = dp_aux_cmd_fifo_tx(aux, msg);
> > > -
> > >       if (ret < 0) {
> > >               if (aux->native) {
> > >                       aux->retry_cnt++;
> > >                       if (!(aux->retry_cnt % MAX_AUX_RETRIES))
> > >                               dp_catalog_aux_update_cfg(aux->catalog);
> > >               }
> > > -             usleep_range(400, 500); /* at least 400us to next try */
> > > -             goto unlock_exit;
> > > -     }
> >
> > 1) dp_catalog_aux_update_cfg(aux->catalog) will not work without
> > dp_catalog_aux_reset(aux->catalog);
> > dp_catalog_aux_reset(aux->catalog) will reset hpd control block and
> > potentially cause pending hpd interrupts got lost.
> > Therefore I think we should not do
> > dp_catalog_aux_update_cfg(aux->catalog) for now.
> > reset aux controller will reset hpd control block probolem will be 
> > fixed
> > at next chipset.
> > after that we can add dp_catalog_aux_update_cfg(aux->catalog) followed
> > by dp_catalog_aux_reset(aux->catalog) back at next chipset.
>
> Hmm ok. So the phy calibration logic that tweaks the tuning values is
> never used? Why can't the phy be tuned while it is active? I don't
> understand why we would ever want to reset the aux phy when changing 
> the
> settings for a retry. Either way, this is not actually changing in this
> patch so it would be another patch to remove this code.
ok,
> > 2) according to DP specification, aux read/write failed have to wait 
> > at
> > least 400us before next try can start.
> > Otherwise, DP compliant test will failed
>
> Yes. The caller of this function, drm_dp_dpcd_access(), has the delay
> already
>
>                 if (ret != 0 && ret != -ETIMEDOUT) {
>                         usleep_range(AUX_RETRY_INTERVAL,
>                                      AUX_RETRY_INTERVAL + 100);
>                 }
>
> so this delay here is redundant.
yes, you are right. This is enough.