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.
>
> 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.
