linux-kernel - Re: [PATCH 00/17] fbdev: Remove FBINFO_DEFAULT and FBINFO_FLAG

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Date:   Tue, 11 Jul 2023 18:04:41 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Helge Deller <deller@....de>
Cc:     Sam Ravnborg <sam@...nborg.org>,
        Thomas Zimmermann <tzimmermann@...e.de>, javierm@...hat.com,
        linux-fbdev@...r.kernel.org, kvm@...r.kernel.org,
        linux-hyperv@...r.kernel.org, linux-sh@...r.kernel.org,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org,
        amd-gfx@...ts.freedesktop.org, linux-geode@...ts.infradead.org,
        dri-devel@...ts.freedesktop.org, linux-input@...r.kernel.org,
        linux-nvidia@...ts.surfsouth.com, linux-omap@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org,
        linux-arm-kernel@...ts.infradead.org, linux-media@...r.kernel.org
Subject: Re: [PATCH 00/17] fbdev: Remove FBINFO_DEFAULT and
 FBINFO_FLAG_DEFAULT flags

Hi Helge,

On Tue, Jul 11, 2023 at 5:26 PM Helge Deller <deller@....de> wrote:
> On 7/11/23 16:47, Sam Ravnborg wrote:
> > On Tue, Jul 11, 2023 at 08:24:40AM +0200, Thomas Zimmermann wrote:
> >> Am 10.07.23 um 19:19 schrieb Sam Ravnborg:
> >>> On Mon, Jul 10, 2023 at 02:50:04PM +0200, Thomas Zimmermann wrote:
> >>>> Remove the unused flags FBINFO_DEFAULT and FBINFO_FLAG_DEFAULT from
> >>>> fbdev and drivers, as briefly discussed at [1]. Both flags were maybe
> >>>> useful when fbdev had special handling for driver modules. With
> >>>> commit 376b3ff54c9a ("fbdev: Nuke FBINFO_MODULE"), they are both 0
> >>>> and have no further effect.
> >>>>
> >>>> Patches 1 to 7 remove FBINFO_DEFAULT from drivers. Patches 2 to 5
> >>>> split this by the way the fb_info struct is being allocated. All flags
> >>>> are cleared to zero during the allocation.
> >>>>
> >>>> Patches 8 to 16 do the same for FBINFO_FLAG_DEFAULT. Patch 8 fixes
> >>>> an actual bug in how arch/sh uses the tokne for struct fb_videomode,
> >>>> which is unrelated.
> >>>>
> >>>> Patch 17 removes both flag constants from <linux/fb.h>
> >>>
> >>> We have a few more flags that are unused - should they be nuked too?
> >>> FBINFO_HWACCEL_FILLRECT
> >>> FBINFO_HWACCEL_ROTATE
> >>> FBINFO_HWACCEL_XPAN
> >>
> >> It seems those are there for completeness. Nothing sets _ROTATE,
>
> I think some fbdev drivers had hardware acceleration for ROTATE in the
> past. HWACCEL_XPAN is still in some drivers.
>
> >> the others are simply never checked. According to the comments,
> >> some are required, some are optional. I don't know what that
> >> means.
>
> I think it's OK if you remove those flags which aren't used anywhere,
> e.g. FBINFO_HWACCEL_ROTATE.

Indeed.

> >> IIRC there were complains about performance when Daniel tried to remove
> >> fbcon acceleration, so not all _HWACCEL_ flags are unneeded.
>
> Correct. I think COPYAREA and FILLRECT are the bare minimum to accelerate
> fbcon, IMAGEBLIT is for showing the tux penguin (?),
> XPAN/YPAN and YWRAP for some hardware screen panning needed by some drivers
> (not sure if this is still used as I don't have such hardware, Geert?).

Yes, they are used.  Anything that is handled in drivers/video/fbdev/core/
is used:

$ git grep  HWACCEL_ -- drivers/video/fbdev/core/
drivers/video/fbdev/core/fbcon.c:       if ((info->flags &
FBINFO_HWACCEL_COPYAREA) &&
drivers/video/fbdev/core/fbcon.c:           !(info->flags &
FBINFO_HWACCEL_DISABLED))
drivers/video/fbdev/core/fbcon.c:       int good_pan = (cap &
FBINFO_HWACCEL_YPAN) &&
drivers/video/fbdev/core/fbcon.c:       int good_wrap = (cap &
FBINFO_HWACCEL_YWRAP) &&
drivers/video/fbdev/core/fbcon.c:       int fast_copyarea = (cap &
FBINFO_HWACCEL_COPYAREA) &&
drivers/video/fbdev/core/fbcon.c:               !(cap &
FBINFO_HWACCEL_DISABLED);
drivers/video/fbdev/core/fbcon.c:       int fast_imageblit = (cap &
FBINFO_HWACCEL_IMAGEBLIT) &&
drivers/video/fbdev/core/fbcon.c:               !(cap &
FBINFO_HWACCEL_DISABLED);

BTW, I'm surprised FBINFO_HWACCEL_FILLRECT is not handled.
But looking at the full history, it never was...

> >> Leaving them in for reference/completeness might be an option; or not. I
> >> have no strong feelings about those flags.
>
> I'd say drop FBINFO_HWACCEL_ROTATE at least ?

Agreed.

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