[PATCH v5 2/4] drm: introduce drm_writeback_connector_init_with_encoder() API
Abhinav Kumar
quic_abhinavk at quicinc.com
Wed Mar 23 18:28:56 UTC 2022
Hi Liviu
Thanks for the review.
On 3/23/2022 9:46 AM, Liviu Dudau wrote:
> On Mon, Mar 21, 2022 at 04:56:43PM -0700, Abhinav Kumar wrote:
>> For vendors drivers which pass an already allocated and
>> initialized encoder especially for cases where the encoder
>> hardware is shared OR the writeback encoder shares the resources
>> with the rest of the display pipeline introduce a new API,
>> drm_writeback_connector_init_with_encoder() which expects
>> an initialized encoder as a parameter and only sets up the
>> writeback connector.
>>
>> changes in v5:
>> - reorder this change to come before in the series
>> to avoid incorrect functionality in subsequent changes
>> - continue using struct drm_encoder instead of
>> struct drm_encoder * and switch it in next change
>>
>> Signed-off-by: Abhinav Kumar <quic_abhinavk at quicinc.com>
>
> Hi Abhinav,
>
>> ---
>> drivers/gpu/drm/drm_writeback.c | 143 ++++++++++++++++++++++++++++------------
>> include/drm/drm_writeback.h | 5 ++
>> 2 files changed, 106 insertions(+), 42 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_writeback.c b/drivers/gpu/drm/drm_writeback.c
>> index dc2ef12..abe78b9 100644
>> --- a/drivers/gpu/drm/drm_writeback.c
>> +++ b/drivers/gpu/drm/drm_writeback.c
>> @@ -149,37 +149,15 @@ static const struct drm_encoder_funcs drm_writeback_encoder_funcs = {
>> .destroy = drm_encoder_cleanup,
>> };
>>
>> -/**
>> - * drm_writeback_connector_init - Initialize a writeback connector and its properties
>> - * @dev: DRM device
>> - * @wb_connector: Writeback connector to initialize
>> - * @con_funcs: Connector funcs vtable
>> - * @enc_helper_funcs: Encoder helper funcs vtable to be used by the internal encoder
>> - * @formats: Array of supported pixel formats for the writeback engine
>> - * @n_formats: Length of the formats array
>> - * @possible_crtcs: possible crtcs for the internal writeback encoder
>> - *
>> - * This function creates the writeback-connector-specific properties if they
>> - * have not been already created, initializes the connector as
>> - * type DRM_MODE_CONNECTOR_WRITEBACK, and correctly initializes the property
>> - * values. It will also create an internal encoder associated with the
>> - * drm_writeback_connector and set it to use the @enc_helper_funcs vtable for
>> - * the encoder helper.
>> - *
>> - * Drivers should always use this function instead of drm_connector_init() to
>> - * set up writeback connectors.
>> - *
>> - * Returns: 0 on success, or a negative error code
>> - */
>> -int drm_writeback_connector_init(struct drm_device *dev,
>> - struct drm_writeback_connector *wb_connector,
>> - const struct drm_connector_funcs *con_funcs,
>> - const struct drm_encoder_helper_funcs *enc_helper_funcs,
>> - const u32 *formats, int n_formats, uint32_t possible_crtcs)
>> +static int drm_writeback_connector_setup(struct drm_device *dev,
>> + struct drm_writeback_connector *wb_connector,
>> + const struct drm_connector_funcs *con_funcs, const u32 *formats,
>> + int n_formats)
>> {
>> struct drm_property_blob *blob;
>> - struct drm_connector *connector = &wb_connector->base;
>> struct drm_mode_config *config = &dev->mode_config;
>> + struct drm_connector *connector = &wb_connector->base;
>> +
>
> Point of this reordering the statements is...?
This diff can be avoided. There was no reason to reorder this. I will
remove this re-order.
>
>> int ret = create_writeback_properties(dev);
>>
>> if (ret != 0)
>> @@ -187,18 +165,10 @@ int drm_writeback_connector_init(struct drm_device *dev,
>>
>> blob = drm_property_create_blob(dev, n_formats * sizeof(*formats),
>> formats);
>> - if (IS_ERR(blob))
>> - return PTR_ERR(blob);
>> -
>> - drm_encoder_helper_add(&wb_connector->encoder, enc_helper_funcs);
>> -
>> - wb_connector->encoder.possible_crtcs = possible_crtcs;
>> -
>> - ret = drm_encoder_init(dev, &wb_connector->encoder,
>> - &drm_writeback_encoder_funcs,
>> - DRM_MODE_ENCODER_VIRTUAL, NULL);
>> - if (ret)
>> - goto fail;
>> + if (IS_ERR(blob)) {
>> + ret = PTR_ERR(blob);
>> + return ret;
>> + }
>
> I don't see why you have changed the earlier code to store the result of PTR_ERR into
> ret other than to help your debugging. I suggest that you keep the existing code that
> returns PTR_ERR(blob) directly and you will have a nicer diff stat as well.
Sure, i can fix this for a smaller diff stat.
>
>>
>> connector->interlace_allowed = 0;
>>
>> @@ -237,13 +207,102 @@ int drm_writeback_connector_init(struct drm_device *dev,
>> attach_fail:
>> drm_connector_cleanup(connector);
>> connector_fail:
>> - drm_encoder_cleanup(&wb_connector->encoder);
>> -fail:
>> drm_property_blob_put(blob);
>> return ret;
>> }
>> +
>> +/**
>> + * drm_writeback_connector_init - Initialize a writeback connector and its properties
>> + * @dev: DRM device
>> + * @wb_connector: Writeback connector to initialize
>> + * @con_funcs: Connector funcs vtable
>> + * @enc_helper_funcs: Encoder helper funcs vtable to be used by the internal encoder
>> + * @formats: Array of supported pixel formats for the writeback engine
>> + * @n_formats: Length of the formats array
>> + * @possible_crtcs: possible crtcs for the internal writeback encoder
>> + *
>> + * This function creates the writeback-connector-specific properties if they
>> + * have not been already created, initializes the connector as
>> + * type DRM_MODE_CONNECTOR_WRITEBACK, and correctly initializes the property
>> + * values. It will also create an internal encoder associated with the
>> + * drm_writeback_connector and set it to use the @enc_helper_funcs vtable for
>> + * the encoder helper.
>> + *
>> + * Drivers should always use this function instead of drm_connector_init() to
>> + * set up writeback connectors.
>> + *
>> + * Returns: 0 on success, or a negative error code
>> + */
>> +int drm_writeback_connector_init(struct drm_device *dev,
>> + struct drm_writeback_connector *wb_connector,
>> + const struct drm_connector_funcs *con_funcs,
>> + const struct drm_encoder_helper_funcs *enc_helper_funcs,
>> + const u32 *formats, int n_formats, uint32_t possible_crtcs)
>> +{
>> + int ret = 0;
>> +
>> + drm_encoder_helper_add(&wb_connector->encoder, enc_helper_funcs);
>> +
>> + wb_connector->encoder.possible_crtcs = possible_crtcs;
>> +
>> + ret = drm_encoder_init(dev, &wb_connector->encoder,
>> + &drm_writeback_encoder_funcs,
>> + DRM_MODE_ENCODER_VIRTUAL, NULL);
>> + if (ret)
>> + return ret;
>> +
>> + ret = drm_writeback_connector_setup(dev, wb_connector, con_funcs, formats,
>> + n_formats);
>> +
>> + if (ret)
>> + drm_encoder_cleanup(&wb_connector->encoder);
>> +
>> + return ret;
>> +}
>> EXPORT_SYMBOL(drm_writeback_connector_init);
>>
>> +/**
>> + * drm_writeback_connector_init_with_encoder - Initialize a writeback connector and its properties
>> + * using the encoder which already assigned and initialized
>> + *
>> + * @dev: DRM device
>> + * @wb_connector: Writeback connector to initialize
>> + * @con_funcs: Connector funcs vtable
>> + * @enc_helper_funcs: Encoder helper funcs vtable to be used by the internal encoder
>> + * @formats: Array of supported pixel formats for the writeback engine
>> + * @n_formats: Length of the formats array
>> + *
>> + * This function creates the writeback-connector-specific properties if they
>> + * have not been already created, initializes the connector as
>> + * type DRM_MODE_CONNECTOR_WRITEBACK, and correctly initializes the property
>> + * values.
>> + *
>> + * This function assumes that the drm_writebac_connector's encoder has already been
>
> spelling: writeback
Ack. will fix this.
>
>> + * created and initialized before invoking this function.
>> + *
>> + * In addition, this function also assumes that callers of this API will manage
>> + * assigning the encoder helper functions, possible_crtcs and any other encoder
>> + * specific operation which is otherwise handled by drm_writeback_connector_init().
>> + *
>> + * Drivers should always use this function instead of drm_connector_init() to
>> + * set up writeback connectors.
>
> .... if they want to manage themselves the lifetime of the associated encoder.
>
> We're not trying to replace drm_writeback_connector_init() function here, only to
> provide an alternative function to call for special cases.
Yes, we are trying to provide an alternative function call for special
case where the encoder is a shared encoder and/or where the resources of
the writeback encoder are shared with other hardware blocks.
I can add that comment to this function's doc.
>
>> + *
>> + * Returns: 0 on success, or a negative error code
>> + */
>> +int drm_writeback_connector_init_with_encoder(struct drm_device *dev,
>> + struct drm_writeback_connector *wb_connector,
>> + const struct drm_connector_funcs *con_funcs, const u32 *formats,
>> + int n_formats)
>
> Where is the encoder parameter? Isn't that the reason why the function is called
> `_with_encoder`?
The encoder parameter is skipped here because this function assumes that
wb_connector->encoder has already been initialized, setup with functions
and its possible_crts have already been set prior to calling this
function like the vc4 example shows. So this function doesnt need an
explicit encoder parameter. Let me know if thats a concern.
>
> I think there might have been too many version of these patchsets and things are
> starting to be confusing. Please revisit the series without rushing and come up with
> a plan of action. My understanding of watching this series has been that you're
> trying to come up with a function that does *connector* initialisation but skips the
> *encoder* initialisation because it might have been already done by the driver. The
> idea will be then to have a function `drm_writeback_connector_init_with_encoder()`
> that does *all* the work that `drm_writeback_connector_init()` does at the moment minus
> the encoder initialisation part. Then `drm_writeback_connector_init()` only
> initialises the internal encoder and calls `drm_writeback_connector_init_with_encoder()`.
> There is no need to have the `drm_writeback_connector_setup()` function at all.
>
> Best regards,
> Liviu
>
I agree there have been a 4 revisions prior to this because of the way
this affects the existing writeback drivers. So initial revision was a
bit intrusive into other drivers (which was just mostly a take over from
the previous patchset posted by the Co-developer ) and since rev3 we
have decided to have a separate API
drm_writeback_connector_init_with_encoder() so that existing clients are
unaffected and it works seamlessly under the hood.
Only clients which already embed an encoder (vc4) and the new ones which
have special encoder requirements like the MSM driver for which I am
preparing these changes for will use the new API.
Apologies for the revisions, but thanks to some great feedback from you
and laurent its shaping up nicely and reaching its conclusion I feel.
So i think this revision is pretty close to being clean thanks to the
feedback you gave on rev4. Between rev4 and this one I didnt drastically
change the design other than re-ordering the changes to avoid the
intermediate patches having an incorrect state for the vc4 encoder. So
all your comments related to the encoder_cleanup() and vc4's encoder not
getting initialized would have gotten addressed but overall concept
remained same.
You are right, we are trying to come up with a function which does
connector initialization but skips the encoder part because that has
already been done in the client side of this API ( hence _with_encoder()
name ). The "_with_encoder" indicates that the caller already has an
encoder for the writeback connector which is being passed so there is no
need to pass the encoder again.
I thought this addresses all the concerns posted in the previous series.
So are you suggesting something like below?
1) rename drm_writeback_connector_setup() to
drm_writeback_connector_init_with_encoder()
(essentially thats what will end up happening )
2) Inside drm_writeback_connector_init() check:
drm_writeback_connector_init(.....)
{
if (!wb_conn->encoder)
initialize the encoder
call drm_writeback_**_init_with_encoder()
}
This will also work but have the foll concerns/questions:
1) Will drm_writeback_connector_init_with_encoder() be exported if we
change as per your suggestion or will all clients continue to use
drm_writeback_connector_init() only? We wanted to have a separate
function for new clients.
2) How will we detect that encoder needs to be initialized without it
being a pointer which happens in the later change. So ordering becomes
an issue.
Thats why I thought this is the best way to address the comments and
keep the functionality intact with each change.
Let me know if I have misunderstood some comment or idea.
>
>> +{
>> + int ret = 0;
>> +
>> + ret = drm_writeback_connector_setup(dev, wb_connector, con_funcs, formats,
>> + n_formats);
>> +
>> + return ret;
>> +}
>> +EXPORT_SYMBOL(drm_writeback_connector_init_with_encoder);
>> +
>> int drm_writeback_set_fb(struct drm_connector_state *conn_state,
>> struct drm_framebuffer *fb)
>> {
>> diff --git a/include/drm/drm_writeback.h b/include/drm/drm_writeback.h
>> index db6214f..0093bab 100644
>> --- a/include/drm/drm_writeback.h
>> +++ b/include/drm/drm_writeback.h
>> @@ -152,6 +152,11 @@ int drm_writeback_connector_init(struct drm_device *dev,
>> const struct drm_encoder_helper_funcs *enc_helper_funcs,
>> const u32 *formats, int n_formats, uint32_t possible_crtcs);
>>
>> +int drm_writeback_connector_init_with_encoder(struct drm_device *dev,
>> + struct drm_writeback_connector *wb_connector,
>> + const struct drm_connector_funcs *con_funcs, const u32 *formats,
>> + int n_formats);
>> +
>> int drm_writeback_set_fb(struct drm_connector_state *conn_state,
>> struct drm_framebuffer *fb);
>>
>> --
>> 2.7.4
>>
>
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