Re: [PATCH 1/6] drm: allow real encoder to be passed for drm_writeback_connector

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

On Fri, Mar 11, 2022 at 10:46:13AM +0300, Dmitry Baryshkov wrote:
> On Fri, 11 Mar 2022 at 04:50, Abhinav Kumar <quic_abhinavk@quicinc.com> wrote:
> >
> > For some vendor driver implementations, display hardware can
> > be shared between the encoder used for writeback and the physical
> > display.
> >
> > In addition resources such as clocks and interrupts can
> > also be shared between writeback and the real encoder.
> >
> > To accommodate such vendor drivers and hardware, allow
> > real encoder to be passed for drm_writeback_connector.
> >
> > Co-developed-by: Kandpal Suraj <suraj.kandpal@intel.com>
> > Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
> > ---
> >  drivers/gpu/drm/drm_writeback.c |  8 ++++----
> >  include/drm/drm_writeback.h     | 13 +++++++++++--
> >  2 files changed, 15 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_writeback.c b/drivers/gpu/drm/drm_writeback.c
> > index dccf4504..4dad687 100644
> > --- a/drivers/gpu/drm/drm_writeback.c
> > +++ b/drivers/gpu/drm/drm_writeback.c
> > @@ -189,8 +189,8 @@ int drm_writeback_connector_init(struct drm_device *dev,
> >         if (IS_ERR(blob))
> >                 return PTR_ERR(blob);
> >
> > -       drm_encoder_helper_add(&wb_connector->encoder, enc_helper_funcs);
> > -       ret = drm_encoder_init(dev, &wb_connector->encoder,
> > +       drm_encoder_helper_add(wb_connector->encoder, enc_helper_funcs);
> > +       ret = drm_encoder_init(dev, wb_connector->encoder,
> >                                &drm_writeback_encoder_funcs,
> >                                DRM_MODE_ENCODER_VIRTUAL, NULL);
> 
> If the encoder is provided by a separate driver, it might use a
> different set of encoder funcs.

More than that, if the encoder is provided externally but doesn't have
custom operations, I don't really see the point of having an external
encoder in the first place.

Has this series been tested with a driver that needs to provide an
encoder, to make sure it fits the purpose ?

> I'd suggest checking whether the wb_connector->encoder is NULL here.
> If it is, allocate one using drmm_kzalloc and init it.
> If it is not NULL, assume that it has been initialized already, so
> skip the drm_encoder_init() and just call the drm_encoder_helper_add()
> 
> >         if (ret)
> > @@ -204,7 +204,7 @@ int drm_writeback_connector_init(struct drm_device *dev,
> >                 goto connector_fail;
> >
> >         ret = drm_connector_attach_encoder(connector,
> > -                                               &wb_connector->encoder);
> > +                                               wb_connector->encoder);
> >         if (ret)
> >                 goto attach_fail;
> >
> > @@ -233,7 +233,7 @@ int drm_writeback_connector_init(struct drm_device *dev,
> >  attach_fail:
> >         drm_connector_cleanup(connector);
> >  connector_fail:
> > -       drm_encoder_cleanup(&wb_connector->encoder);
> > +       drm_encoder_cleanup(wb_connector->encoder);
> >  fail:
> >         drm_property_blob_put(blob);
> >         return ret;
> > diff --git a/include/drm/drm_writeback.h b/include/drm/drm_writeback.h
> > index 9697d27..0ba266e 100644
> > --- a/include/drm/drm_writeback.h
> > +++ b/include/drm/drm_writeback.h
> > @@ -25,13 +25,22 @@ struct drm_writeback_connector {
> >         struct drm_connector base;
> >
> >         /**
> > -        * @encoder: Internal encoder used by the connector to fulfill
> > +        * @encoder: handle to drm_encoder used by the connector to fulfill
> >          * the DRM framework requirements. The users of the
> >          * @drm_writeback_connector control the behaviour of the @encoder
> >          * by passing the @enc_funcs parameter to drm_writeback_connector_init()
> >          * function.
> > +        *
> > +        * For some vendor drivers, the hardware resources are shared between
> > +        * writeback encoder and rest of the display pipeline.
> > +        * To accommodate such cases, encoder is a handle to the real encoder
> > +        * hardware.
> > +        *
> > +        * For current existing writeback users, this shall continue to be the
> > +        * embedded encoder for the writeback connector.
> > +        *
> >          */
> > -       struct drm_encoder encoder;
> > +       struct drm_encoder *encoder;
> >
> >         /**
> >          * @pixel_formats_blob_ptr:

-- 
Regards,

Laurent Pinchart