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

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Message-ID: <CANq1E4TN4_NNs32LBcNWeDC2jUtT2TCYHfYeummEC5-TQn7BpA@mail.gmail.com>
Date:	Sat, 26 Sep 2015 20:13:05 +0200
From:	David Herrmann <dh.herrmann@...il.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Alex Deucher <alexdeucher@...il.com>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	linux-fbdev <linux-fbdev@...r.kernel.org>,
	Teddy Wang <teddy.wang@...iconmotion.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	DRI Development <dri-devel@...ts.freedesktop.org>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Arnaud Patard <apatard@...driva.com>,
	Dave Airlie <airlied@...hat.com>,
	Sudip Mukherjee <sudipm.mukherjee@...il.com>
Subject: Re: No more new fbdev drivers, please

Hi

On Sat, Sep 26, 2015 at 8:01 PM, Geert Uytterhoeven
<geert@...ux-m68k.org> wrote:
> Hi Alex,
>
> On Sat, Sep 26, 2015 at 7:07 PM, Alex Deucher <alexdeucher@...il.com> wrote:
>> On Sat, Sep 26, 2015 at 4:28 AM, Geert Uytterhoeven
>> <geert@...ux-m68k.org> wrote:
>>> On Thu, Sep 24, 2015 at 5:23 PM, Daniel Vetter <daniel@...ll.ch> wrote:
>>>> On Thu, Sep 24, 2015 at 02:46:21PM +0200, Thomas Petazzoni wrote:
>>>>> Or are there some plans to make the writing of DRM drivers for very
>>>>> simple/trivial devices a bit simpler?
>>>>
>>>> Since years I'm trying to sell someone on implementing support for
>>>> drm_simple_outputs which would collapse the crtc->encoder->connector
>>>> chain into 1 entity. Would be trivial to implement and then trivial to
>>>> write simple drivers on top of that. And besides that drm already has
>>>> piles of reallly simple drivers with just one output and one framebuffer.
>>>>
>>>> There's no reason not to use drm for gfx drivers at all.
>>>
>>> Good to hear that!
>>>
>>> For the (mailing list) record, can you please provide some explicit pointers
>>> to these existing really simple drivers?
>>
>> See the tilcdc, ast, mgag200, and udl drivers for example.
>
> Thanks for the list!
>
> The smallest of these (udl) still counts in at ca. 2800 LoC, while there are
> several fbdev drivers that have less than 200 LoC.
> Granted, these really small ones support a single fixed video mode only, but
> you can write a simple fbdev driver with mode setting in less than 1000 LoC.
>
> I'm sure DRM can do better?

Is counting lines really the level of the discussion to go here?

DRM is a big set of helpers, nothing else. If many trivial, small
drivers share common code, developers are more than welcome to
contribute them to drm-core and help making drivers less complex.

As Daniel mentioned, the connector+encoder+crtc combination is one of
those simplifications that would make sense if more such drivers are
added. Furthermore, the not-yet-merged SimpleDRM driver is one example
how to implement multiple of those dumb-fb drivers with a shared
code-base.

Thanks
David
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