Re: [PATCH 2/2] drm/dumb-buffers: document abuses in the UAPI document

[Thomas Zimmermann]

Hi

Am 26.02.26 um 07:37 schrieb Icenowy Zheng:
> Although the current DRM_IOCTL_MODE_CREATE_DUMB interface design only
> suits linear buffers, some KMS drivers abuse it for AFBC framebuffers.
>
> Mention it in the interface document, and clarifying that it's not
> recommended.
>
> Signed-off-by: Icenowy Zheng <zhengxingda@xxxxxxxxxxx>
> ---
>   include/uapi/drm/drm_mode.h | 4 ++++
>   1 file changed, 4 insertions(+)
>
> diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
> index cbbbfc1dfe2b8..02b6fa7ade355 100644
> --- a/include/uapi/drm/drm_mode.h
> +++ b/include/uapi/drm/drm_mode.h
> @@ -1256,6 +1256,10 @@ struct drm_mode_crtc_page_flip_target {

Since you're at it, you should move the line at [1] right here as the 
first sentence of this paragraph. Then continue with 'Do not attempt'.

With that change, the previous paragraphs refer to pixel formats and the 
final one refers to framebuffer layout.


>    * Do not attempt to allocate anything but linear framebuffer memory
>    * with single-plane RGB data. Allocation of other framebuffer
>    * layouts requires dedicated ioctls in the respective DRM driver.
> + * There exists drivers exploiting this interface for framebuffers

'exists user-space software'

> + * with modifiers other than DRM_FORMAT_MOD_LINEAR, but this is

Rather 'with non-linear layout'.  The reference to MOD_LINEAR seems out 
of place here.

> + * incorrect usage with undefined behavior, and should not be
> + * replicated.

Best regards
Thomas

[1] 
https://elixir.bootlin.com/linux/v6.19/source/include/uapi/drm/drm_mode.h#L1216

>    */
>   struct drm_mode_create_dumb {
>   	__u32 height;

--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)