[PATCH 1/6] drm: allow real encoder to be passed for drm_writeback_connector

[Abhinav Kumar]

Hi Daniel

On 3/17/2022 3:01 AM, Daniel Vetter wrote:
> On Fri, Mar 11, 2022 at 10:05:53AM +0200, Laurent Pinchart wrote:
>> On Fri, Mar 11, 2022 at 10:46:13AM +0300, Dmitry Baryshkov wrote:
>>> On Fri, 11 Mar 2022 at 04:50, Abhinav Kumar <quic_abhinavk at quicinc.com> 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.
>>>>
>>>> Co-developed-by: Kandpal Suraj <suraj.kandpal at intel.com>
>>>> Signed-off-by: Abhinav Kumar <quic_abhinavk at quicinc.com>
>>>> ---
>>>>   drivers/gpu/drm/drm_writeback.c |  8 ++++----
>>>>   include/drm/drm_writeback.h     | 13 +++++++++++--
>>>>   2 files changed, 15 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/drm_writeback.c b/drivers/gpu/drm/drm_writeback.c
>>>> index dccf4504..4dad687 100644
>>>> --- a/drivers/gpu/drm/drm_writeback.c
>>>> +++ b/drivers/gpu/drm/drm_writeback.c
>>>> @@ -189,8 +189,8 @@ int drm_writeback_connector_init(struct drm_device *dev,
>>>>          if (IS_ERR(blob))
>>>>                  return PTR_ERR(blob);
>>>>
>>>> -       drm_encoder_helper_add(&wb_connector->encoder, enc_helper_funcs);
>>>> -       ret = drm_encoder_init(dev, &wb_connector->encoder,
>>>> +       drm_encoder_helper_add(wb_connector->encoder, enc_helper_funcs);
>>>> +       ret = drm_encoder_init(dev, wb_connector->encoder,
>>>>                                 &drm_writeback_encoder_funcs,
>>>>                                 DRM_MODE_ENCODER_VIRTUAL, NULL);
>>>
>>> If the encoder is provided by a separate driver, it might use a
>>> different set of encoder funcs.
>>
>> More than that, if the encoder is provided externally but doesn't have
>> custom operations, I don't really see the point of having an external
>> encoder in the first place.
>>
>> Has this series been tested with a driver that needs to provide an
>> encoder, to make sure it fits the purpose ?
> 
> Also, can we not force all drivers to do this setup that don't need it? We
> have a ton of kms drivers, forcing unnecessary busiwork on drivers is
> really not good.
> -Daniel
No, there will not be any requirement forced for existing drivers.
A new API will be exposed for new clients which setup the encoder.
> 
>>
>>> I'd suggest checking whether the wb_connector->encoder is NULL here.
>>> If it is, allocate one using drmm_kzalloc and init it.
>>> If it is not NULL, assume that it has been initialized already, so
>>> skip the drm_encoder_init() and just call the drm_encoder_helper_add()
>>>
>>>>          if (ret)
>>>> @@ -204,7 +204,7 @@ int drm_writeback_connector_init(struct drm_device *dev,
>>>>                  goto connector_fail;
>>>>
>>>>          ret = drm_connector_attach_encoder(connector,
>>>> -                                               &wb_connector->encoder);
>>>> +                                               wb_connector->encoder);
>>>>          if (ret)
>>>>                  goto attach_fail;
>>>>
>>>> @@ -233,7 +233,7 @@ int drm_writeback_connector_init(struct drm_device *dev,
>>>>   attach_fail:
>>>>          drm_connector_cleanup(connector);
>>>>   connector_fail:
>>>> -       drm_encoder_cleanup(&wb_connector->encoder);
>>>> +       drm_encoder_cleanup(wb_connector->encoder);
>>>>   fail:
>>>>          drm_property_blob_put(blob);
>>>>          return ret;
>>>> diff --git a/include/drm/drm_writeback.h b/include/drm/drm_writeback.h
>>>> index 9697d27..0ba266e 100644
>>>> --- a/include/drm/drm_writeback.h
>>>> +++ b/include/drm/drm_writeback.h
>>>> @@ -25,13 +25,22 @@ 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;
>>>> +       struct drm_encoder *encoder;
>>>>
>>>>          /**
>>>>           * @pixel_formats_blob_ptr:
>>
>> -- 
>> Regards,
>>
>> Laurent Pinchart
>