[PATCH v2 15/15] drm/mgag200: Replace VRAM helpers with SHMEM helpers

[Thomas Zimmermann]

Hi

Am 12.05.20 um 12:30 schrieb Emil Velikov:
> On Tue, 12 May 2020 at 09:43, Thomas Zimmermann <tzimmermann at suse.de> wrote:
>>
>> The VRAM helpers managed the framebuffer memory for mgag200. This came
>> with several problems, as some MGA device require the scanout address
>> to be located at VRAM offset 0. It's incompatible with the page-flip
>> semantics of DRM's atomic modesettting. With atomic modesetting, old and
>> new framebuffers have to be located in VRAM at the same time. So at least
>> one of them has to reside at a non-0 offset.
>>
>> This patch replaces VRAM helpers with SHMEM helpers. GEM SHMEM buffers
>> reside in system memory, and are shadow-copied into VRAM during page
>> flips. The shadow copy always starts at VRAM offset 0.
>>
> I suspect MGAG200_FLAG_HW_BUG_NO_STARTADD is left around for
> documentation purposes?

Yes. For now, that flag seems to be the best documentation of the HW issue.

Besides, there's another known bug in several MGAs: scanlines may not
cross the 4 MiB boundary. If we ever have to work around that problem,
NO_STARTADD might become useful again. One can either scanout from 0, or
align FB scanlines around the 4 MiB boundary; but not both.

> 
> I've made a few small comments, but regardless the series is:
> Acked-by: Emil Velikov <emil.velikov at collabora.com>

Thanks!

Best regards
Thomas

> 
> -Emil
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer

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