Question about sRGB framebuffer support

Ville Syrjälä ville.syrjala at
Wed May 6 07:44:57 UTC 2020

On Tue, May 05, 2020 at 01:24:16PM +0300, Artem Mygaiev wrote:
> Hello all
> I am currently working on DRM/KMS driver for Fresco Logic FL2000 USB display
> controller [1]. I have already implemented a POC driver [2] which is working for
> me, although there are still plenty of things to improve or fix, of course.
> So far I have one thing that I somehow cannot find in DRM/KMS documentation or
> existing drivers: how to tell the system that HW expects sRGB (i.e. non-linear)
> color encoding in framebuffers? This is a HW limitation that I cannot influence
> by configuration.

Does it do something to process the data that requires linearization
or why does it care about the gamma applied to the data? In a typical
use case the data is just passed through unless the user asks otherwise,
so it doesn't matter much what gamma was used. Though most displays
probably expect something resembling sRGB gamma by default, so that's
presumably what most things generate, and images/videos/etc. pretty
much always have gamma already applied when they are produced.

> Any pointers are greatly appreciated.
> [1]
> [2]
> Best regards,
>  -- Artem
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Ville Syrjälä

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