Re: [PATCH] drm/doc: Document that modifiers are always required for fb

[Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>]

Acked-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>

On Thu, Sep 17, 2020 at 6:48 PM Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
>
> Even for legacy userspace, since otherwise GETFB2 is broken and if you
> switch between modifier-less and modifier-aware compositors, smooth
> transitions break.
>
> Also it's just best practice to make sure modifiers are invariant for
> a given drm_fb, and that a modifier-aware kms drivers only has one
> place to store them, ignoring any old implicit bo flags or whatever
> else might float around.
>
> Motivated by some irc discussion with Bas about amdgpu modifier
> support.
>
> Acked-by: Simon Ser <contact@emersion.fr>
> Acked-by: Daniel Stone <daniels@collabora.com>
> Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>
> Fixes: 455e00f1412f ("drm: Add getfb2 ioctl")
> Cc: Daniel Stone <daniels@collabora.com>
> Cc: Juston Li <juston.li@intel.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
> Cc: Marek Olšák <maraeo@gmail.com>
> Cc: "Wentland, Harry" <harry.wentland@amd.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> ---
> Sending this out again to double-check there's no objections or concerns.
> From what I understand looking at the code the latest modifier patches for
> amdgpu follow this now.
>
> Cheers, Daniel
> ---
>  include/drm/drm_mode_config.h | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
>
> diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
> index a18f73eb3cf6..5ffbb4ed5b35 100644
> --- a/include/drm/drm_mode_config.h
> +++ b/include/drm/drm_mode_config.h
> @@ -58,6 +58,12 @@ struct drm_mode_config_funcs {
>          * actual modifier used if the request doesn't have it specified,
>          * ie. when (@mode_cmd->flags & DRM_MODE_FB_MODIFIERS) == 0.
>          *
> +        * IMPORTANT: These implied modifiers for legacy userspace must be
> +        * stored in struct &drm_framebuffer, including all relevant metadata
> +        * like &drm_framebuffer.pitches and &drm_framebuffer.offsets if the
> +        * modifier enables additional planes beyond the fourcc pixel format
> +        * code. This is required by the GETFB2 ioctl.
> +        *
>          * If the parameters are deemed valid and the backing storage objects in
>          * the underlying memory manager all exist, then the driver allocates
>          * a new &drm_framebuffer structure, subclassed to contain
> @@ -915,6 +921,13 @@ struct drm_mode_config {
>          * @allow_fb_modifiers:
>          *
>          * Whether the driver supports fb modifiers in the ADDFB2.1 ioctl call.
> +        *
> +        * IMPORTANT:
> +        *
> +        * If this is set the driver must fill out the full implicit modifier
> +        * information in their &drm_mode_config_funcs.fb_create hook for legacy
> +        * userspace which does not set modifiers. Otherwise the GETFB2 ioctl is
> +        * broken for modifier aware userspace.
>          */
>         bool allow_fb_modifiers;
>
> --
> 2.28.0
>
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