[RFC PATCH 0/2] drm/mgag200: Use 24bit format in VRAM

[Thomas Zimmermann]

Hi

Am 12.04.23 um 15:39 schrieb Jocelyn Falempe:
> The bandwidth between system memory and VRAM is very limited
> on G200.
> So when using a 32bit framebuffer on system memory, convert it to 24bit
> when copying the frame to the VRAM, this allows to go 33% faster.
> Converting the format on the fly is negligible, even on low end CPU.

I'm skeptical about this idea. We emulated a number of formats in 
simpledrm and got a lot of flames and pushback. The argument was that we 
should export the formats that hardware supports and not pretend to 
support anything else. The only exception allowed was emulating 
XRGB8888, because it's the common ground hat everything in userspace 
supports.

I see that this is a bit different from your patches, but not so much. 
When userspace wants 32-bit XRGB, it should get it if possible.

I'd rather suggest to set the console to 16 bit and also resort the 
formats array. It is supposed to be sorted by preference. RGB565 should 
maybe be the top most entry, followed by RGB888. Then you'd have to 
teach userspace to respect these settings. I'm not sure if all 
compositors do.

Best regards
Thomas

> 
> [PATCH 1/2] drm/mgag200: simplify offset and scale computation.
> [PATCH 2/2] drm/mgag200: Use 24bit format in VRAM
> 
> drivers/gpu/drm/mgag200/mgag200_mode.c | 87 ++++++++++++++++++++++++++++++++++++---------------------------------------------------
>   1 file changed, 36 insertions(+), 51 deletions(-)
> 
> 
> 

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