[PATCH] drm/fourcc: add LINEAR modifiers with an exact pitch alignment

[Marek Olšák]

Missed 2 lines from the diff:

+#define DRM_FORMAT_MOD_LINEAR_PITCH_ALIGN_128B fourcc_mod_code(NONE, 2)
+#define DRM_FORMAT_MOD_LINEAR_PITCH_ALIGN_256B fourcc_mod_code(NONE, 3)

Marek

On Sun, Dec 15, 2024 at 3:53 PM Marek Olšák <maraeo at gmail.com> wrote:

> The comment explains the problem with DRM_FORMAT_MOD_LINEAR.
>
> Signed-off-by: Marek Olšák <marek.olsak at amd.com>
>
> diff --git a/include/uapi/drm/drm_fourcc.h b/include/uapi/drm/drm_fourcc.h
> index 78abd819fd62e..8ec4163429014 100644
> --- a/include/uapi/drm/drm_fourcc.h
> +++ b/include/uapi/drm/drm_fourcc.h
> @@ -484,9 +484,27 @@ extern "C" {
>   * modifier (e.g. not setting DRM_MODE_FB_MODIFIERS in the DRM_ADDFB2
> ioctl),
>   * which tells the driver to also take driver-internal information into
> account
>   * and so might actually result in a tiled framebuffer.
> + *
> + * WARNING:
> + * There are drivers out there that expose DRM_FORMAT_MOD_LINEAR, but only
> + * support a certain pitch alignment and can't import images with this
> modifier
> + * if the pitch alignment isn't exactly the one supported. They can
> however
> + * allocate images with this modifier and other drivers can import them
> only
> + * if they support the same pitch alignment. Thus, DRM_FORMAT_MOD_LINEAR
> is
> + * fundamentically incompatible across devices and is the only modifier
> that
> + * has a chance of not working. The PITCH_ALIGN modifiers should be used
> + * instead.
>   */
>  #define DRM_FORMAT_MOD_LINEAR  fourcc_mod_code(NONE, 0)
>
> +/* Linear layout modifiers with an explicit pitch alignment in bytes.
> + * Exposing this modifier requires that the pitch alignment is exactly
> + * the number in the definition.
> + */
> +#define DRM_FORMAT_MOD_LINEAR_PITCH_ALIGN_64B fourcc_mod_code(NONE, 1)
>
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