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

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Message-ID: <bf439387-6b13-0fd9-f61b-1a5cbf731187@gmx.de>
Date:   Tue, 11 Jul 2023 17:24:01 +0200
From:   Helge Deller <deller@....de>
To:     Sam Ravnborg <sam@...nborg.org>,
        Thomas Zimmermann <tzimmermann@...e.de>
Cc:     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

On 7/11/23 16:47, Sam Ravnborg wrote:
> Hi Thomas,
>
> On Tue, Jul 11, 2023 at 08:24:40AM +0200, Thomas Zimmermann wrote:
>> Hi Sam
>>
>> Am 10.07.23 um 19:19 schrieb Sam Ravnborg:
>>> Hi Thomas,
>>>
>>> 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.

>> 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?).

>> 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 ?

>>> Unused as in no references from fbdev/core/*
>>>
>>> I would rather see one series nuke all unused FBINFO flags in one go.
>>> Assuming my quick grep are right and the above can be dropped.
>>
>> I would not want to extend this series. I'm removing _DEFAULT as it's
>> absolutely pointless and confusing.

Yes, Ok.

Helge