[Freedreno] [PATCH v4 03/20] drm: allow real encoder to be passed for drm_writeback_connector
Abhinav Kumar
quic_abhinavk at quicinc.com
Mon Apr 25 16:25:44 UTC 2022
On 4/25/2022 3:50 AM, Dmitry Baryshkov wrote:
> On Sun, 24 Apr 2022 at 22:59, Laurent Pinchart
> <laurent.pinchart at ideasonboard.com> 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.)
>
Agree with your comment Dmitry and thats why I was suggesting to let
drm_writeback_connector.encoder remain a valid pointer to avoid
discrepancies.
If we go with option (1), this change as-it-is is the best way to go.
If we go with option (2), to drop the encoder field and just rename
encoder ---> internal_encoder, it will still work for existing users.
But I would prefer that goes as a separate change then because MSM
doesn't really need this ( and at this point even other drivers don't )
I am still ready to post the change separately and do basic validation
with our boards.
>>
>>> Hope this clarifies it.
>>>
>>>>>> Signed-off-by: Abhinav Kumar <quic_abhinavk at quicinc.com>
>>>>>> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov at 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:
>>
>> --
>> Regards,
>>
>> Laurent Pinchart
>
>
>
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