[PATCH 03/28] drm/writeback: Define function to get drm_connector from writeback

[Kandpal, Suraj]

> -----Original Message-----
> From: Dmitry Baryshkov <dmitry.baryshkov at oss.qualcomm.com>
> Sent: Saturday, July 26, 2025 6:04 PM
> To: Kandpal, Suraj <suraj.kandpal at intel.com>
> Cc: dri-devel at lists.freedesktop.org; intel-xe at lists.freedesktop.org; intel-
> gfx at lists.freedesktop.org; Nautiyal, Ankit K <ankit.k.nautiyal at intel.com>;
> Murthy, Arun R <arun.r.murthy at intel.com>; Shankar, Uma
> <uma.shankar at intel.com>
> Subject: Re: [PATCH 03/28] drm/writeback: Define function to get
> drm_connector from writeback
> 
> On Fri, Jul 25, 2025 at 10:33:44AM +0530, Suraj Kandpal wrote:
> > Now that drm_connector may not always be embedded within
> > drm_writeback_connector, let's define a function which either uses the
> > writeback helper hook that returns the drm_connector associated with
> > the drm_writeback_connector or just return the drm_connector embedded
> > inside drm_writeback_connector if the helper hook is not present. Lets
> > use this function and call it whenever drm_connector is required
> > mostly when connector helper private funcs need to be fetched.
> >
> > Signed-off-by: Suraj Kandpal <suraj.kandpal at intel.com>
> > ---
> >  drivers/gpu/drm/drm_writeback.c | 33
> > ++++++++++++++++++++++++++-------
> >  1 file changed, 26 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_writeback.c
> > b/drivers/gpu/drm/drm_writeback.c index e9f7123270d6..d610cb827975
> > 100644
> > --- a/drivers/gpu/drm/drm_writeback.c
> > +++ b/drivers/gpu/drm/drm_writeback.c
> > @@ -120,6 +120,18 @@ drm_connector_to_writeback(struct
> drm_connector
> > *connector)  }  EXPORT_SYMBOL(drm_connector_to_writeback);
> >
> > +static struct drm_connector *
> > +drm_connector_from_writeback(struct drm_writeback_connector
> > +*wb_connector) {
> > +	const struct drm_writeback_connector_helper_funcs *funcs =
> > +		wb_connector->helper_private;
> > +
> > +	if (funcs && funcs->get_connector_from_writeback)
> > +		return funcs-
> >get_connector_from_writeback(wb_connector);
> 
> The get_connector_from_writeback() and
> drm_writeback_connector_helper_funcs should be moved to this patch.

Want to keep them separate since they themselves introduce a lot of changes on of them
has use introducing a new writeback_helper_function structure.


> 
> However it feels really awkward to make drm_writeback_connector, which is
> a wrapper around the drm_connector, to use some external DRM connector.
> A quick grepping reveals API (which you missed) that expects
> drm_writeback_connector.base to be a valid connector. And it would be very
> hard to catch sunch an API later on.

Also seems like I did miss the fence_get_driver_name one which is an easy fix or
did you see anything else.
Really don't see any other problematic areas

> 
> If you want to use DRM framwework, while retaining intel_connector for
> writeback connectors, I'd suggest following slightly different path: extract
> common parts of drm_writeback_connector into a common structure, and
> use it within the DRM core. Then provide functions to fetch drm_connector
> from that struct or fetch it from drm_connector.

Causes a lot of changes in the drm_writeback_connector structure causing every other driver
Using this to change how they essentially call upon drm_writeback_connector. This API
was to provide more non invasive way to give everyone another alternative.

Regards,
Suraj Kandpal

> 
> 
> > +
> > +	return &wb_connector->base;
> > +}
> > +
> >  static int create_writeback_properties(struct drm_device *dev)  {
> >  	struct drm_property *prop;
> > @@ -478,6 +490,7 @@ drm_writeback_connector_init_with_conn(struct
> drm_device *dev, struct drm_connec
> >  	if (ret)
> >  		goto connector_fail;
> >
> > +	drm_writeback_connector_helper_add(wb_connector, wb_funcs);
> >  	INIT_LIST_HEAD(&wb_connector->job_queue);
> >  	spin_lock_init(&wb_connector->job_lock);
> >
> > @@ -527,13 +540,15 @@ int drm_writeback_set_fb(struct
> > drm_connector_state *conn_state,
> >
> >  int drm_writeback_prepare_job(struct drm_writeback_job *job)  {
> > -	struct drm_writeback_connector *connector = job->connector;
> > +	struct drm_writeback_connector *wb_connector = job->connector;
> > +	struct drm_connector *connector =
> > +		drm_connector_from_writeback(wb_connector);
> >  	const struct drm_connector_helper_funcs *funcs =
> > -		connector->base.helper_private;
> > +		connector->helper_private;
> >  	int ret;
> >
> >  	if (funcs->prepare_writeback_job) {
> > -		ret = funcs->prepare_writeback_job(connector, job);
> > +		ret = funcs->prepare_writeback_job(wb_connector, job);
> >  		if (ret < 0)
> >  			return ret;
> >  	}
> > @@ -579,12 +594,14 @@ EXPORT_SYMBOL(drm_writeback_queue_job);
> >
> >  void drm_writeback_cleanup_job(struct drm_writeback_job *job)  {
> > -	struct drm_writeback_connector *connector = job->connector;
> > +	struct drm_writeback_connector *wb_connector = job->connector;
> > +	struct drm_connector *connector =
> > +		drm_connector_from_writeback(wb_connector);
> >  	const struct drm_connector_helper_funcs *funcs =
> > -		connector->base.helper_private;
> > +		connector->helper_private;
> >
> >  	if (job->prepared && funcs->cleanup_writeback_job)
> > -		funcs->cleanup_writeback_job(connector, job);
> > +		funcs->cleanup_writeback_job(wb_connector, job);
> >
> >  	if (job->fb)
> >  		drm_framebuffer_put(job->fb);
> > @@ -665,9 +682,11 @@
> EXPORT_SYMBOL(drm_writeback_signal_completion);
> >  struct dma_fence *
> >  drm_writeback_get_out_fence(struct drm_writeback_connector
> > *wb_connector)  {
> > +	struct drm_connector *connector =
> > +		drm_connector_from_writeback(wb_connector);
> >  	struct dma_fence *fence;
> >
> > -	if (WARN_ON(wb_connector->base.connector_type !=
> > +	if (WARN_ON(connector->connector_type !=
> >  		    DRM_MODE_CONNECTOR_WRITEBACK))
> >  		return NULL;
> >
> > --
> > 2.34.1
> >
> 
> --
> With best wishes
> Dmitry