Re: [PATCH 1/7] drm/hisilicon/hibmc: Fix preferred depth and bpp

[Javier Martinez Canillas <javierm@redhat.com>]

On 11/18/22 14:18, Thomas Zimmermann wrote:

[...]

>>
>> In the cover letter you said "color depth is the number of color and alpha bits
>> that affect image composition" but it should be "only the number of color bits
>> excluding the alpha bits" a better description right?
> 
> I was looking at drm_fourcc.c, where alpha formats, such as ARGB888, 
> have alpha included in their depth value. [1] Alpha obviously effects 
> image composition.
> 
> But meaning of these terms is somewhat fuzzy, as the command-line 
> arguments of video= include a BPP value that is more similar to DRM's 
> depth value.
>

I see.
 
> [1] 
> https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/drm_fourcc.c#L175
> 
>>
>> I also wonder if instead of using a 24 magic number, TRUE_COLOR_DEPTH constant
>> macro or XRGB8888_COLOR_DEPTH could be defined?
> 
> Please not. What we should do is to replace the preferred depth and bpp 
> with a single format constant (as 4cc or drm_format_info) that 
> designates a preferred default. From that format constant, the values 
> exported to userspace and fbdev emulation should be retrieved automatically.
> 
> If anything, I'd add a TODO item to convert the DRM codebase.
>

Right. That makes more sense indeed.
 

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat