drm: Include the encoder itself in possible_clones

The docs say possible_clones should always include the encoder itself.
Since most drivers don't want to deal with the complexities of cloning
let's allow them to set possible_clones=0 and instead we'll fix that
up in the core.

We can't put this special case into drm_encoder_init() because drivers
will have to fill up possible_clones after adding all the relevant
encoders. Otherwise they wouldn't know the proper encoder indexes to
use. So we'll just do it just before registering the device.

v2: Don't set the bit if possible_clones!=0 so that the
    validation (coming soon) will WARN (Thomas)
    Fix up the docs to allow possible_clones==0 (Daniel)
    .late_register() is too late, introduce drm_mode_config_validate()
    which gets called _before_ we register the char device (Daniel)

Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200211162208.16224-2-ville.syrjala@linux.intel.com
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 3 insertions, 1 deletions

diff --git a/include/drm/drm_encoder.h b/include/drm/drm_encoder.h
index 4370e039c015..34b7213bfab6 100644
--- a/include/drm/drm_encoder.h
+++ b/include/drm/drm_encoder.h
@@ -159,7 +159,9 @@ struct drm_encoder {
 	 * encoders can be used in a cloned configuration, they both should have
 	 * each another bits set.
 	 *
-	 * In reality almost every driver gets this wrong.
+	 * As an exception to the above rule if the driver doesn't implement
+	 * any cloning it can leave @possible_clones set to 0. The core will
+	 * automagically fix this up by setting the bit for the encoder itself.
 	 *
 	 * Note that since encoder objects can't be hotplugged the assigned indices
 	 * are stable and hence known before registering all objects.