On Sun, 24 Apr 2022 at 22:59, Laurent Pinchart
<laurent.pinchart@xxxxxxxxxxxxxxxx> wrote:
>
> Hi Abhinav,
>
> On Sun, Apr 24, 2022 at 11:23:20AM -0700, Abhinav Kumar wrote:
> > On 4/24/2022 11:12 AM, Abhinav Kumar wrote:
> > > On 4/24/2022 7:50 AM, Laurent Pinchart wrote:
> > >> 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.
>
> Users of drm_writeback_connector_init_with_encoder() handle the encoder
> themselves, they can simply ignore drm_writeback_connector.encoder. The
> documentation of the encoder field needs to be updated though (I'd do so
> in the previous patch), to clearly mention that the field is valid only
> when using drm_writeback_connector_init(), not when calling
> drm_writeback_connector_init_with_encoder().
If we allow it to be unitialized, it might end with hard-to-trace
bugs, additional conditions, etc.
In my opnion we should:
- either make drm_writeback_connector.encoder a valid pointer
- or drop the field completely.
And up to some point I'd vote for the second option. The code using
internal_encoder can continue using it directly. The code using
drm_writeback_connector_init_with_encoder() will manage encoder on
their own. We will loose a single entry point for wb's encoder, but do
we really need it? (Frankly speaking I didn't check.)
>
> > 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:
>
> --
> Regards,
>
> Laurent Pinchart
--
With best wishes
Dmitry
