[PATCH 12/12] drm/modifiers: Enforce consistency between the cap an IN_FORMATS

[Lucas Stach]

Am Dienstag, dem 13.04.2021 um 11:49 +0200 schrieb Daniel Vetter:
> It's very confusing for userspace to have to deal with inconsistencies
> here, and some drivers screwed this up a bit. Most just ommitted the
> format list when they meant to say that only linear modifier is
> allowed, but some also meant that only implied modifiers are
> acceptable (because actually none of the planes registered supported
> modifiers).

For a lot of the embedded display drivers that never had any out-of-
band tiling meta shared with the GPU part, the implied modifier is
actually DRM_FORMAT_MOD_LINEAR, so maybe that's where some of the
confusion about needing to specify the modifier list comes from.

> Now that this is all done consistently across all drivers, document
> the rules and enforce it in the drm core.

This clarification looks good to me.

Reviewed-by: Lucas Stach <l.stach at pengutronix.de>

> Cc: Pekka Paalanen <pekka.paalanen at collabora.com>
> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> Cc: Maxime Ripard <mripard at kernel.org>
> Cc: Thomas Zimmermann <tzimmermann at suse.de>
> Cc: David Airlie <airlied at linux.ie>
> Cc: Daniel Vetter <daniel at ffwll.ch>
> ---
>  drivers/gpu/drm/drm_plane.c   | 16 +++++++++++++++-
>  include/drm/drm_mode_config.h |  2 ++
>  2 files changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
> index 0dd43882fe7c..16a7e3e57f7f 100644
> --- a/drivers/gpu/drm/drm_plane.c
> +++ b/drivers/gpu/drm/drm_plane.c
> @@ -128,6 +128,11 @@
>   *     pairs supported by this plane. The blob is a struct
>   *     drm_format_modifier_blob. Without this property the plane doesn't
>   *     support buffers with modifiers. Userspace cannot change this property.
> + *
> + *     Note that userspace can check the DRM_CAP_ADDFB2_MODIFIERS driver
> + *     capability for general modifier support. If this flag is set then every
> + *     plane will have the IN_FORMATS property, even when it only supports
> + *     DRM_FORMAT_MOD_LINEAR.
>   */
>  
> 
> 
> 
> 
> 
> 
> 
>  static unsigned int drm_num_planes(struct drm_device *dev)
> @@ -277,8 +282,14 @@ static int __drm_universal_plane_init(struct drm_device *dev,
>  			format_modifier_count++;
>  	}
>  
> 
> 
> 
> 
> 
> 
> 
> -	if (format_modifier_count)
> +	/* autoset the cap and check for consistency across all planes */
> +	if (format_modifier_count) {
> +		WARN_ON(!config->allow_fb_modifiers &&
> +			!list_empty(&config->plane_list));
>  		config->allow_fb_modifiers = true;
> +	} else {
> +		WARN_ON(config->allow_fb_modifiers);
> +	}
>  
> 
> 
> 
> 
> 
> 
> 
>  	plane->modifier_count = format_modifier_count;
>  	plane->modifiers = kmalloc_array(format_modifier_count,
> @@ -360,6 +371,9 @@ static int __drm_universal_plane_init(struct drm_device *dev,
>   * drm_universal_plane_init() to let the DRM managed resource infrastructure
>   * take care of cleanup and deallocation.
>   *
> + * Drivers supporting modifiers must set @format_modifiers on all their planes,
> + * even those that only support DRM_FORMAT_MOD_LINEAR.
> + *
>   * Returns:
>   * Zero on success, error code on failure.
>   */
> diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
> index ab424ddd7665..1ddf7783fdf7 100644
> --- a/include/drm/drm_mode_config.h
> +++ b/include/drm/drm_mode_config.h
> @@ -909,6 +909,8 @@ struct drm_mode_config {
>  	 * @allow_fb_modifiers:
>  	 *
>  	 * Whether the driver supports fb modifiers in the ADDFB2.1 ioctl call.
> +	 * Note that drivers should not set this directly, it is automatically
> +	 * set in drm_universal_plane_init().
>  	 *
>  	 * IMPORTANT:
>  	 *