RE: [PATCH v6 2/8] drm/msm/dp: wait for hpd high before aux transaction

["Sankeerth Billakanti (QUIC)" <quic_sbillaka@quicinc.com>]

Hi Doug,

> On Wed, Mar 30, 2022 at 9:03 AM Sankeerth Billakanti
> <quic_sbillaka@quicinc.com> wrote:
> >
> > The source device should ensure the sink is ready before proceeding to
> > read the sink capability or performing any aux transactions. The sink
> 
> s/performing/perform
> 
> > will indicate its readiness by asserting the HPD line. The controller
> > driver needs to wait for the hpd line to be asserted by the sink
> > before performing any aux transactions.
> >
> > The eDP sink is assumed to be always connected. It needs power from
> > the source and its HPD line will be asserted only after the panel is
> > powered on. The panel power will be enabled from the panel-edp driver
> > and only after that, the hpd line will be asserted.
> >
> > Whereas for DP, the sink can be hotplugged and unplugged anytime. The
> > hpd line gets asserted to indicate the sink is connected and ready.
> > Hence there is no need to wait for the hpd line to be asserted for a DP sink.
> >
> > Signed-off-by: Sankeerth Billakanti <quic_sbillaka@quicinc.com>
> > ---
> >
> > Changes in v6:
> >   - Wait for hpd high only for eDP
> >   - Split into smaller patches
> >
> >  drivers/gpu/drm/msm/dp/dp_aux.c     | 13 ++++++++++++-
> >  drivers/gpu/drm/msm/dp/dp_aux.h     |  3 ++-
> >  drivers/gpu/drm/msm/dp/dp_catalog.c | 13 +++++++++++++
> > drivers/gpu/drm/msm/dp/dp_catalog.h |  1 +
> > drivers/gpu/drm/msm/dp/dp_display.c |  3 ++-
> >  5 files changed, 30 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/dp/dp_aux.c
> > b/drivers/gpu/drm/msm/dp/dp_aux.c index 6d36f63..a217c80 100644
> > --- a/drivers/gpu/drm/msm/dp/dp_aux.c
> > +++ b/drivers/gpu/drm/msm/dp/dp_aux.c
> > @@ -36,6 +36,7 @@ struct dp_aux_private {
> >         bool initted;
> >         u32 offset;
> >         u32 segment;
> > +       bool is_edp;
> >
> >         struct drm_dp_aux dp_aux;
> >  };
> > @@ -337,6 +338,14 @@ static ssize_t dp_aux_transfer(struct drm_dp_aux
> *dp_aux,
> >                 goto exit;
> >         }
> >
> > +       if (aux->is_edp) {
> 
> Adding a comment about _why_ you're doing this just for eDP would
> probably be a good idea. Like maybe:
> 
> /*
>  * For eDP it's important to give a reasonably long wait here for HPD
>  * to be asserted. This is because the panel driver may have _just_
>  * turned on the panel and then tried to do an AUX transfer. The panel
>  * driver has no way of knowing when the panel is ready, so it's up
>  * to us to wait. For DP we never get into this situation so let's
>  * avoid ever doing the extra long wait for DP.
>  */
> 
> 

Okay. Will add it

> > @@ -491,7 +500,8 @@ void dp_aux_unregister(struct drm_dp_aux
> *dp_aux)
> >         drm_dp_aux_unregister(dp_aux);  }
> >
> > -struct drm_dp_aux *dp_aux_get(struct device *dev, struct dp_catalog
> > *catalog)
> > +struct drm_dp_aux *dp_aux_get(struct device *dev, struct dp_catalog
> *catalog,
> > +                               bool is_edp)
> 
> nit: I think your indentation of the 2nd line isn't quite right.
> 
>

I moved bool is_edp into the next line. In vim , it was sowing fine. I'll check
 
> > diff --git a/drivers/gpu/drm/msm/dp/dp_aux.h
> > b/drivers/gpu/drm/msm/dp/dp_aux.h index 82afc8d..c99aeec 100644
> > --- a/drivers/gpu/drm/msm/dp/dp_aux.h
> > +++ b/drivers/gpu/drm/msm/dp/dp_aux.h
> > @@ -16,7 +16,8 @@ void dp_aux_init(struct drm_dp_aux *dp_aux);  void
> > dp_aux_deinit(struct drm_dp_aux *dp_aux);  void dp_aux_reconfig(struct
> > drm_dp_aux *dp_aux);
> >
> > -struct drm_dp_aux *dp_aux_get(struct device *dev, struct dp_catalog
> > *catalog);
> > +struct drm_dp_aux *dp_aux_get(struct device *dev, struct dp_catalog
> *catalog,
> > +                               bool is_edp);
> 
> nit: I think your indentation of the 2nd line isn't quite right.
> 

I'll check

> 
> Things are pretty much nits, so FWIW:
> 
> Reviewed-by: Douglas Anderson <dianders@chromium.org>

Thank you,
Sankeerth