Re: [PATCH v3 3/4] drm: require a non_NULL drm_crtc.primary

[Pekka Paalanen <ppaalanen@gmail.com>]

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On Fri, 11 Dec 2020 13:06:17 +0000
Simon Ser <contact@emersion.fr> wrote:

> If a CRTC is missing a legacy primary plane pointer, a lot of things
> will be broken for user-space: fbdev stops working and the entire legacy
> uAPI stops working.
> 
> Require all drivers to populate drm_crtc.primary to prevent these
> issues. Warn if it's NULL.
> 
> Signed-off-by: Simon Ser <contact@emersion.fr>
> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Pekka Paalanen <ppaalanen@gmail.com>

Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>

> ---
>  drivers/gpu/drm/drm_mode_config.c | 3 +++
>  drivers/gpu/drm/drm_plane.c       | 2 +-
>  2 files changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
> index 2c73a60e8765..fbe680035129 100644
> --- a/drivers/gpu/drm/drm_mode_config.c
> +++ b/drivers/gpu/drm/drm_mode_config.c
> @@ -639,6 +639,9 @@ void drm_mode_config_validate(struct drm_device *dev)
>  	}
>  
>  	drm_for_each_crtc(crtc, dev) {
> +		WARN(!crtc->primary, "Missing primary plane on [CRTC:%d:%s]\n",
> +		     crtc->base.id, crtc->name);
> +
>  		if (crtc->primary) {
>  			WARN(!(crtc->primary->possible_crtcs & BIT(crtc->index)),
>  			     "Bogus primary plane possible_crtcs: [PLANE:%d:%s] must be compatible with [CRTC:%d:%s]\n",
> diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
> index 5d33ca9f0032..49b0a8b9ac02 100644
> --- a/drivers/gpu/drm/drm_plane.c
> +++ b/drivers/gpu/drm/drm_plane.c
> @@ -57,7 +57,7 @@
>   * 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
> - * drivers should provide one primary plane per CRTC to avoid surprising legacy
> + * drivers must provide one primary plane per CRTC to avoid surprising legacy
>   * userspace too much.
>   */
>  


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