linux-kernel - Re: [PATCH 3/6] drm: fourcc byteorder: add bigendian support to drm_mode_legacy_fb

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Date:   Thu, 27 Apr 2017 09:52:59 +0900
From:   Michel Dänzer <michel@...nzer.net>
To:     Gerd Hoffmann <kraxel@...hat.com>
Cc:     Daniel Vetter <daniel.vetter@...el.com>,
        dri-devel@...ts.freedesktop.org,
        open list <linux-kernel@...r.kernel.org>,
        amd-gfx@...ts.freedesktop.org
Subject: Re: [PATCH 3/6] drm: fourcc byteorder: add bigendian support to
 drm_mode_legacy_fb_format

On 26/04/17 09:11 PM, Gerd Hoffmann wrote:
>   Hi,
> 
>>>> Just to reiterate, this won't work for the radeon driver, which programs
>>>> the GPU to use (effectively, per the current definition that these are
>>>> little endian GPU formats) DRM_FORMAT_XRGB8888 with pre-R600 and
>>>> DRM_FORMAT_BGRX8888 with >= R600.
>>>
>>> Hmm, ok, how does bigendian fbdev emulation work on pre-R600 then?
>>
>> Using a GPU byte swapping mechanism which only affects CPU access to
>> video RAM.
> 
> That is done using the RADEON_TILING_SWAP_{16,32}BIT flag mentioned in
> another thread?

Right.


> What about dumb bos?  You've mentioned the swap flag isn't used for
> those.  Which implies they are in little endian byte order (both gpu and
> cpu view).

Right, AFAICT from looking at the code.


> Does the modesetting driver work correctly on that hardware?

Not sure.


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer