linux-kernel - Re: No more new fbdev drivers, please

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Message-ID: <20150929070728.GA3383@phenom.ffwll.local>
Date:	Tue, 29 Sep 2015 09:07:28 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Noralf Trønnes <noralf@...nnes.org>
Cc:	Emil Velikov <emil.l.velikov@...il.com>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-fbdev <linux-fbdev@...r.kernel.org>,
	DRI Development <dri-devel@...ts.freedesktop.org>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Teddy Wang <teddy.wang@...iconmotion.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Dave Airlie <airlied@...hat.com>,
	Sudip Mukherjee <sudipm.mukherjee@...il.com>
Subject: Re: No more new fbdev drivers, please

On Tue, Sep 29, 2015 at 12:51:38AM +0200, Noralf Trønnes wrote:
> 
> Den 27.09.2015 18:08, skrev Emil Velikov:
> >Hi all,
> >
> >On 27 September 2015 at 14:09, Noralf Trønnes <noralf@...nnes.org> wrote:
> >>Den 24.09.2015 14:27, skrev Tomi Valkeinen:
> >>>Hi all,
> >>>
> >>>fbdev is (more or less) maintained, but it's a deprecated framework. All
> >>>new Linux display drivers should be done on DRM.
> >>>
> >>>So let's not add any more new fbdev drivers.
> >>>
> >>>I will continue to maintain the current fbdev drivers, and I don't mind
> >>>adding some new features to those current drivers, as long as the amount
> >>>of code required to add the features stays sensible.
> >>>
> >>>I see we have three fbdev drivers in staging: xgifb, fbtft and sm750fb,
> >>>and the question is what to do with those.
> >>>
> >>>xgifb was added in 2010, and is still in staging.
> >>>
> >>>fbtft looks like maybe some kind of framework on top of fbdev, with
> >>>fbtft specific subdrivers... I didn't look at it in detail, but my gut
> >>>says "never".
> >>
> >>I have done some work [1] to try and make fbtft look more like the rest
> >>of the kernel (doc [2]), but that work will result in an almost complete
> >>rewrite of fbtft.
> > From a very quick skim fbtft looks pretty much like drm/panel. We
> >presently have 30+ 'simple' dsi panels, plus a bunch of spi ones. Have
> >you had a look at these ?
> 
> Thanks, that was useful.
> I can use drm_panel to setup the controller (prepare) and do backlight
> (enable/disable), but I need a way to send framebuffer changes.
> I could do this:
> 
> struct tinydrm_panel_funcs {
>         int (*update)(struct drm_framebuffer *fb,
>                       struct drm_gem_cma_object *cma_obj,
>                       unsigned flags, unsigned color,
>                       struct drm_clip_rect *clips, unsigned num_clips);
> };
> 
> struct tinydrm_panel {
>         struct drm_panel panel;
>         u32 width;
>         u32 height;
>         void *dev_private;
> 
>         const struct tinydrm_panel_funcs *funcs;
> };

I'm not sure whether putting the manual-update stuff into drm_panel is a
good idea - it's transport/bus (spi, dsi, ...) specific. Not sure how to
best solve that.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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