linux-kernel - Re: [RFC PATCH 0/3] staging: remove fbdev drivers

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Date:   Thu, 8 Dec 2016 13:15:56 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        Noralf Trønnes <noralf@...nnes.org>,
        Sudip Mukherjee <sudipm.mukherjee@...il.com>,
        Teddy Wang <teddy.wang@...iconmotion.com>,
        Arnaud Patard <arnaud.patard@...-net.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 0/3] staging: remove fbdev drivers

On Thu, Dec 8, 2016 at 11:10 AM, Daniel Vetter <daniel@...ll.ch> wrote:
> On Thu, Dec 08, 2016 at 12:01:19PM +1100, Benjamin Herrenschmidt wrote:
>> On Wed, 2016-11-23 at 10:03 +0200, Tomi Valkeinen wrote:
>> > Since the fbdev framework is in maintenance mode and all new display drivers
>> > should be made with the DRM framework, remove the fbdev drivers from staging.
>> >
>> > Note: the patches are created with git format-patch -D, so they can't be
>> > applied. Only for review.
>>
>> I missed the discussion where this decision was made, I admit I am
>> unimpressed by it.
>>
>> DRM drivers don't strike me as suitable for small/slow cores with dumb
>> framebuffers or simple 2D only accel, such as the one found in the ASpeed
>> BMCs.
>
> We have a helper for simple drivers now, if you take into account the
> massive helper libraries for everything that comes along with drm I expect
> if even dumb panels behind slow spi buses drm is now the more suitable
> subsytem.

This has been going on your years:
  1. Fbdev is obsolete, everybody should use DRM instead!
  2. Can you please point me to a small sample driver for a dumb frame buffer?
  3. Several are being written, but none of them is upstream yet.
  4. Goto 1.

>> With drmfb you basically have to shadow everything into memory & copy
>> over everything, and locks you out of simple 2D accel. For a simple text
>> console the result is orders of magnitude slower and memory hungry than
>> a simple fbdev.
>
> Not true, we have full fbdev emulation, and drivers can implement the 2d
> accel in there. And a bunch of them do. It's just that most teams decided
> that this is pointless waste of their time.j
>
>> At least that was the case last I looked at the DRM stuff with Dave,
>> maybe things have changed...
>>
>> Not everything has a powerful 3D GPU.
>
> That's correct, and drm can cope. And compared to fbdev there's a very
> active community who improves&refactors it every kernel release to make it
> even better. Since about 2 years (when atomic landed) we merge new drivers at
> a rate of 2-3 per kernel release, and those new drivers get ever simpler
> and smaller thanks to all this work.

You mean the kind of refactoring that causes severe merge conflicts between
drm-next and Linus' tree about every single day?
(sorry, couldn't resist ;-)

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds