linux-kernel - RE: [RFC PATCH 1/8] drm: writeback: Refactor drm_writeback

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Message-ID: <DM3PPF208195D8D7513998A044E1A54B6D1E328A@DM3PPF208195D8D.namprd11.prod.outlook.com>
Date: Mon, 11 Aug 2025 11:19:26 +0000
From: "Kandpal, Suraj" <suraj.kandpal@...el.com>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>, Dmitry Baryshkov
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Subject: RE: [RFC PATCH 1/8] drm: writeback: Refactor drm_writeback_connector
 structure

> > > > @@ -2305,6 +2360,11 @@ struct drm_connector {
> > > >  	 * @cec: CEC-related data.
> > > >  	 */
> > > >  	struct drm_connector_cec cec;
> > > > +
> > > > +	/**
> > > > +	 * @writeback: Writeback related valriables.
> > > > +	 */
> > > > +	struct drm_writeback_connector writeback;
> > >
> > > No, sorry, that's a bad idea. Most connectors have nothing to do
> > > with writeback, you shouldn't introduce writeback-specific fields here.
> > > drm_writeback_connector happens to be a drm_connector because of
> > > historical reasons (it was decided to reuse the connector API
> > > exposed to userspace instead of exposing a completely separate API
> > > in order to simplify the implementation), but that does not mean
> > > that every connector is related to writeback.
> > >
> > > I don't know what issues the Intel driver(s) have with
> > > drm_writeback_connector, but you shouldn't make things worse for
> > > everybody due to a driver problem.
> >
> > Suraj is trying to solve a problem that in Intel code every
> > drm_connector must be an intel_connector too. His previous attempt
> > resulted in a loose abstraction where drm_writeback_connector.base
> > wasn't initialized in some cases (which is a bad idea IMO).
> >
> > I know the historical reasons for drm_writeback_connector, but I think
> > we can do better now.
> >
> > So, I think, a proper approach would be:
> >
> > struct drm_connector {
> >     // other fields
> >
> >     union {
> >         struct drm_connector_hdmi hdmi; // we already have it
> >         struct drm_connector_wb wb;  // this is new
> >     };
> >
> >     // rest of the fields.
> > };
> 
> I still don't like that. This really doesn't belong here. If anything, the
> drm_connector for writeback belongs to drm_crtc.
> 
> If the issue is that some drivers need a custom drm_connector subclass, then
> I'd rather turn the connector field of drm_writeback_connector into a pointer.
> 

This design or turning drm_connector to inside drm_writeback_connector to a pointer
I am okay either way.

Regards,
Suraj Kandpal

> > I plan to add drm_connector_dp in a similar way, covering DP needs
> > (currently WIP).
> 
> --
> Regards,
> 
> Laurent Pinchart