[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 17:48:07 UTC 2022
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 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:
>
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