On Mon, Apr 25, 2022 at 10:48:07AM -0700, Abhinav Kumar wrote:
> 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.
I don't think we can do that, as that field is used for the internal
encoder :-) It could be renamed to internal_encoder if desired, but not
dropped. I don't mind much either way, as long as we make it clear that
drivers must never reference it directly.
> >>>> 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
