[PATCH v3 4/4] drm: require each CRTC to have a unique primary plane

[Daniel Vetter]

On Fri, Dec 11, 2020 at 2:08 PM Simon Ser <contact at emersion.fr> wrote:
>
> User-space expects to be able to pick a primary plane for each CRTC
> exposed by the driver. Make sure this assumption holds in
> drm_mode_config_validate.
>
> Use the legacy drm_crtc.primary field to check this, because it's
> simpler and we require drivers to set it anyways. Accumulate a set of
> primary planes which are already used for a CRTC in a bitmask. Error out
> if a primary plane is re-used.
>
> v2: new patch
>
> v3:
> - Use u64 instead of __u64 (Jani)
> - Use `unsigned int` instead of `unsigned` (Jani)
>
> Signed-off-by: Simon Ser <contact at emersion.fr>
> Cc: Daniel Vetter <daniel at ffwll.ch>
> Cc: Pekka Paalanen <ppaalanen at gmail.com>
> Cc: Jani Nikula <jani.nikula at linux.intel.com>

Yeah makes sense to also check this.

Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>

> ---
>  drivers/gpu/drm/drm_mode_config.c | 21 +++++++++++++++++++++
>  drivers/gpu/drm/drm_plane.c       |  6 ++++++
>  2 files changed, 27 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
> index fbe680035129..c5cf5624c106 100644
> --- a/drivers/gpu/drm/drm_mode_config.c
> +++ b/drivers/gpu/drm/drm_mode_config.c
> @@ -626,6 +626,9 @@ void drm_mode_config_validate(struct drm_device *dev)
>  {
>         struct drm_encoder *encoder;
>         struct drm_crtc *crtc;
> +       struct drm_plane *plane;
> +       u64 primary_with_crtc = 0, cursor_with_crtc = 0;
> +       unsigned int num_primary = 0;
>
>         if (!drm_core_check_feature(dev, DRIVER_MODESET))
>                 return;
> @@ -647,12 +650,30 @@ void drm_mode_config_validate(struct drm_device *dev)
>                              "Bogus primary plane possible_crtcs: [PLANE:%d:%s] must be compatible with [CRTC:%d:%s]\n",
>                              crtc->primary->base.id, crtc->primary->name,
>                              crtc->base.id, crtc->name);
> +                       WARN(primary_with_crtc & BIT(crtc->primary->index),
> +                            "Primary plane [PLANE:%d:%s] used for two CRTCs",
> +                            crtc->primary->base.id, crtc->primary->name);
> +                       primary_with_crtc |= BIT(crtc->primary->index);
>                 }
>                 if (crtc->cursor) {
>                         WARN(!(crtc->cursor->possible_crtcs & BIT(crtc->index)),
>                              "Bogus cursor plane possible_crtcs: [PLANE:%d:%s] must be compatible with [CRTC:%d:%s]\n",
>                              crtc->cursor->base.id, crtc->cursor->name,
>                              crtc->base.id, crtc->name);
> +                       WARN(cursor_with_crtc & BIT(crtc->cursor->index),
> +                            "Primary plane [PLANE:%d:%s] used for two CRTCs",
> +                            crtc->cursor->base.id, crtc->cursor->name);
> +                       cursor_with_crtc |= BIT(crtc->cursor->index);
>                 }
>         }
> +
> +       drm_for_each_plane(plane, dev) {
> +               if (plane->type == DRM_PLANE_TYPE_PRIMARY) {
> +                       num_primary++;
> +               }
> +       }
> +
> +       WARN(num_primary != dev->mode_config.num_crtc,
> +            "Must have as many primary planes as there are CRTCs, but have %u primary planes and %u CRTCs",
> +            num_primary, dev->mode_config.num_crtc);
>  }
> diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
> index 49b0a8b9ac02..a1f4510efa83 100644
> --- a/drivers/gpu/drm/drm_plane.c
> +++ b/drivers/gpu/drm/drm_plane.c
> @@ -54,6 +54,12 @@
>   * enum drm_plane_type). A plane can be compatible with multiple CRTCs, see
>   * &drm_plane.possible_crtcs.
>   *
> + * Each CRTC must have a unique primary plane userspace can attach to enable
> + * the CRTC. In other words, userspace must be able to attach a different
> + * primary plane to each CRTC at the same time. Primary planes can still be
> + * compatible with multiple CRTCs. There must be exactly as many primary planes
> + * as there are CRTCs.
> + *
>   * Legacy uAPI doesn't expose the primary and cursor planes directly. DRM core
>   * relies on the driver to set the primary and optionally the cursor plane used
>   * for legacy IOCTLs. This is done by calling drm_crtc_init_with_planes(). All
> --
> 2.29.2
>
>


-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch