Re: [PATCH 8/8] drm/modifiers: Enforce consistency between the cap an IN_FORMATS

[Daniel Vetter <daniel.vetter@ffwll.ch>]

On Tue, Apr 27, 2021 at 11:20 AM Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
>
> 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).
>
> Now that this is all done consistently across all drivers, document
> the rules and enforce it in the drm core.
>
> v2:
> - Make the capability a link (Simon)
> - Note that all is lost before 5.1.
>
> Acked-by: Maxime Ripard <maxime@cerno.tech>
> Cc: Simon Ser <contact@emersion.fr>
> Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
> Cc: Pekka Paalanen <pekka.paalanen@collabora.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Maxime Ripard <mripard@kernel.org>
> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: David Airlie <airlied@linux.ie>
> Cc: Daniel Vetter <daniel@ffwll.ch>

Lyude's irc review:

<Lyude> btw danvet (sorry I didn't reply in-line, for some reason I
can't actually seem to find the emails for your allow_fb_modifiers
series in my email client), I just looked over your allow_fb_modifiers
series and everything looks fine with one comment:
https://lore.kernel.org/dri-devel/20210427092018.832258-8-daniel.vetter@ffwll.ch/
we should probably use drm_WARN_ON() here instead
<Lyude> with that fixed: Reviewed-by: Lyude Paul <lyude@redhat.com>

I'll merge the driver patches and respin this one afterwards.
-Daniel

> ---
>  drivers/gpu/drm/drm_plane.c   | 18 +++++++++++++++++-
>  include/drm/drm_mode_config.h |  2 ++
>  2 files changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
> index 0dd43882fe7c..20c7a1665414 100644
> --- a/drivers/gpu/drm/drm_plane.c
> +++ b/drivers/gpu/drm/drm_plane.c
> @@ -128,6 +128,13 @@
>   *     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. Before linux kernel release v5.1 there have been
> + *     various bugs in this area with inconsistencies between the capability
> + *     flag and per-plane properties.
>   */
>
>  static unsigned int drm_num_planes(struct drm_device *dev)
> @@ -277,8 +284,14 @@ 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 +373,9 @@ 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:
>          *
> --
> 2.31.0
>


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