Re: [PATCH v3 3/3] drm: Allow simpledrm to setup its emulated FB as firmware provided

[Daniel Vetter]

On Wed, May 04, 2022 at 01:32:37PM +0200, Javier Martinez Canillas wrote:
> On 5/4/22 12:58, Daniel Vetter wrote:
> > On Tue, May 03, 2022 at 09:15:40AM +0200, Javier Martinez Canillas wrote:
> >> Indicate to fbdev subsystem that the registered framebuffer is provided by
> >> the system firmware, so that it can handle accordingly. For example, would
> >> unregister the FB devices if asked to remove the conflicting framebuffers.
> >>
> >> Add a new DRM_FB_FW field to drm_fbdev_generic_setup() options parameter.
> >> Drivers can use this to indicate the FB helper initialization that the FB
> >> registered is provided by the firmware, so it can be configured as such.
> >>
> >> Suggested-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
> >> Signed-off-by: Javier Martinez Canillas <javierm@xxxxxxxxxx>
> >> Reviewed-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
> >> Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> >> ---
> >>
> >> Changes in v3:
> >> - Drop the firmware local variable (Laurent Pinchart).
> >> - Use DRM_FB_OPTION() since DRM_FB_SET_OPTION() got renamed (kernel test robot).
> > 
> > Just for the record what I brought up on irc already:
> > 
> > FBINFO_MISC_FIRMWARE is purely an internal flag with no uapi impact, and
> > it's only to control whether we nuke this from
> > remove_conflicting_framebuffer or not. Since simpledrm only ever binds
> > against sysfb I think it'd be cleaner to only rely on that, and relegate
> 
> That's not actually true. The OF subsystem also registers "simple-framebuffer"
> devices when there are Device Tree nodes that contain a "simple-framebuffer"
> compatible string. In that case these pdev will also bind against simpledrm.

TIL.

> > that entire FBINFO_MISC_FIRMWARE misc hack to the fbdev dungeons and let
> > it quietly wither away there.
> >
> > Also I'm not a huge fan of these midlayer flags in general :-)
> 
> And while I agree with you that these midlayer flags are horrible, that is
> what any other fbdev that makes use of a firmware-provided framebuffer set,
> so simpledrm emulated fbdev shouldn't be the exception IMO.

So we discussed this a pile more on irc, and at least my take is that
people who run simpledrm but want to combine that with fbdev drivers and
expect it to all work nicely we can probably ignore. At least until all
this sysfb stuff is nicely unified, and at that point we shouldn't need
special flags anymore.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch