Re: [Freedreno] [PATCH v4 03/20] drm: allow real encoder to be passed for drm_writeback_connector

[Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx>]

On 4/24/2022 11:12 AM, Abhinav Kumar wrote:
> Hi Laurent
>
> On 4/24/2022 7:50 AM, Laurent Pinchart wrote:
> > Hi Abhinav,
> >
> > Thank you for the patch.
> >
> > On Fri, Apr 22, 2022 at 04:06:38PM -0700, Abhinav Kumar 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.
> > >
> > > For existing clients, drm_writeback_connector_init() will use
> > > an internal_encoder under the hood and hence no changes will
> > > be needed.
> > >
> > > changes in v7:
> > >     - move this change before the vc4 change in the series
> > >       to minimize the changes to vendor drivers in drm core
> > >       changes
> >
> > Why is this needed ? The drm_writeback_connector functions don't need
> > the drm_encoder after drm_writeback_connector_init() (or
> > drm_writeback_connector_init_with_encoder()) returns.
>
> Sorry I didnt follow this comment. This change log is incorrect, so 
> after changing the previous change in the series and modifying this, no 
> further changes are needed to vc4, so I decided to drop the next change.
> So this change log is incorrect. I can remove this.
>
> Is that what you meant?

So till the previous change, the only user of 
drm_writeback_connector_init_with_encoder() was 
drm_writeback_connector_init() which was still passing its own 
internal_encoder.

Only if the wb_connector->encoder is changed to a pointer, other vendor 
drivers can pass their own encoder to 
drm_writeback_connector_init_with_encoder().

Hence you are right that drm_writeback_connector functions do not need 
drm_encoder after init() returns, but till this change is done, other 
vendor drivers cannot directly call 
drm_writeback_connector_init_with_encoder() because the encoder will not 
be valid till then.

Hope this clarifies it.

> > > Signed-off-by: Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx>
> > > Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
> > > ---
> > >   drivers/gpu/drm/drm_writeback.c | 18 ++++++++++++------
> > >   drivers/gpu/drm/vc4/vc4_txp.c   |  4 ++--
> > >   include/drm/drm_writeback.h     | 22 ++++++++++++++++++++--
> > >   3 files changed, 34 insertions(+), 10 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/drm_writeback.c 
> > > b/drivers/gpu/drm/drm_writeback.c
> > > index 92658ad..0538674 100644
> > > --- a/drivers/gpu/drm/drm_writeback.c
> > > +++ b/drivers/gpu/drm/drm_writeback.c
> > > @@ -180,21 +180,21 @@ int drm_writeback_connector_init(struct 
> > > drm_device *dev,
> > >   {
> > >       int ret = 0;
> > > -    drm_encoder_helper_add(&wb_connector->encoder, enc_helper_funcs);
> > > +    drm_encoder_helper_add(&wb_connector->internal_encoder, 
> > > enc_helper_funcs);
> > > -    wb_connector->encoder.possible_crtcs = possible_crtcs;
> > > +    wb_connector->internal_encoder.possible_crtcs = possible_crtcs;
> > > -    ret = drm_encoder_init(dev, &wb_connector->encoder,
> > > +    ret = drm_encoder_init(dev, &wb_connector->internal_encoder,
> > >                      &drm_writeback_encoder_funcs,
> > >                      DRM_MODE_ENCODER_VIRTUAL, NULL);
> > >       if (ret)
> > >           return ret;
> > > -    ret = drm_writeback_connector_init_with_encoder(dev, 
> > > wb_connector, &wb_connector->encoder,
> > > -            con_funcs, formats, n_formats);
> > > +    ret = drm_writeback_connector_init_with_encoder(dev, wb_connector,
> > > +            &wb_connector->internal_encoder, con_funcs, formats, 
> > > n_formats);
> > >       if (ret)
> > > -        drm_encoder_cleanup(&wb_connector->encoder);
> > > +        drm_encoder_cleanup(&wb_connector->internal_encoder);
> > >       return ret;
> > >   }
> > > @@ -239,6 +239,12 @@ int 
> > > drm_writeback_connector_init_with_encoder(struct drm_device *dev,
> > >       struct drm_mode_config *config = &dev->mode_config;
> > >       int ret = create_writeback_properties(dev);
> > > +    /*
> > > +     * Assign the encoder passed to this API to the wb_connector's 
> > > encoder.
> > > +     * For drm_writeback_connector_init(), this shall be the 
> > > internal_encoder
> > > +     */
> > > +    wb_connector->encoder = enc;
> > > +
> > >       if (ret != 0)
> > >           return ret;
> > > diff --git a/drivers/gpu/drm/vc4/vc4_txp.c 
> > > b/drivers/gpu/drm/vc4/vc4_txp.c
> > > index 3447eb6..7e063a9 100644
> > > --- a/drivers/gpu/drm/vc4/vc4_txp.c
> > > +++ b/drivers/gpu/drm/vc4/vc4_txp.c
> > > @@ -159,7 +159,7 @@ struct vc4_txp {
> > >   static inline struct vc4_txp *encoder_to_vc4_txp(struct drm_encoder 
> > > *encoder)
> > >   {
> > > -    return container_of(encoder, struct vc4_txp, connector.encoder);
> > > +    return container_of(encoder, struct vc4_txp, 
> > > connector.internal_encoder);
> > >   }
> > >   static inline struct vc4_txp *connector_to_vc4_txp(struct 
> > > drm_connector *conn)
> > > @@ -507,7 +507,7 @@ static int vc4_txp_bind(struct device *dev, 
> > > struct device *master, void *data)
> > >       if (ret)
> > >           return ret;
> > > -    encoder = &txp->connector.encoder;
> > > +    encoder = txp->connector.encoder;
> > >       encoder->possible_crtcs = drm_crtc_mask(crtc);
> > >       ret = devm_request_irq(dev, irq, vc4_txp_interrupt, 0,
> > > diff --git a/include/drm/drm_writeback.h b/include/drm/drm_writeback.h
> > > index bb306fa..3fbae9d 100644
> > > --- a/include/drm/drm_writeback.h
> > > +++ b/include/drm/drm_writeback.h
> > > @@ -25,13 +25,31 @@ 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;
> > > +
> > > +    /**
> > > +     * @internal_encoder: internal encoder used by writeback when
> > > +     * drm_writeback_connector_init() is used.
> > > +     * @encoder will be assigned to this for those cases
> > > +     *
> > > +     * This will be unused when 
> > > drm_writeback_connector_init_with_encoder()
> > > +     * is used.
> > >        */
> > > -    struct drm_encoder encoder;
> > > +    struct drm_encoder internal_encoder;
> > >       /**
> > >        * @pixel_formats_blob_ptr: