Hi Laurent
On 4/25/2022 10:32 AM, Laurent Pinchart wrote:
On Mon, Apr 25, 2022 at 01:50:43PM +0300, Dmitry Baryshkov wrote:
On Sun, 24 Apr 2022 at 22:59, Laurent Pinchart wrote:
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.)
As far as I understand, we went for the second option as Abhinav dropped this patch for the next version.
I dropped the patch as there was no agreement yet and I didnt want to block the series as its not really needed now but thats not option 2 because wb_conn->encoder field remains there, just that its unused for users using drm_writeback_connector_init_with_encoder().
I guess what Dmitry is suggesting is just drop that wb_connector->encoder field completely.
Hope this clarifies it.
> Signed-off-by: Abhinav Kumar quic_abhinavk@quicinc.com > Reviewed-by: Dmitry Baryshkov dmitry.baryshkov@linaro.org > --- > 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: