Re: [PATCH v4 02/37] drm/blend: Get a rotation name from it's bitfield

[Louis Chauvet]

On 4/22/26 18:52, Ville Syrjälä wrote:
> On Wed, Apr 22, 2026 at 06:47:59PM +0200, Louis Chauvet wrote:
> > Having the rotation/reflection name from its value can be useful for
> > debugging purpose. Extract the rotation property table and implement
> > drm_get_rotation_name.
> >
> > Reviewed-by: José Expósito <jose.exposito@xxxxxxxxxx>
> > Reviewed-by: Luca Ceresoli <luca.ceresoli@xxxxxxxxxxx>
> > Signed-off-by: Louis Chauvet <louis.chauvet@xxxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/drm_blend.c | 35 ++++++++++++++++++++++++++---------
> >   include/drm/drm_blend.h     |  2 ++
> >   2 files changed, 28 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_blend.c b/drivers/gpu/drm/drm_blend.c
> > index 1f3af27d2418..11d8e13caea3 100644
> > --- a/drivers/gpu/drm/drm_blend.c
> > +++ b/drivers/gpu/drm/drm_blend.c
> > @@ -256,6 +256,31 @@ int drm_plane_create_alpha_property(struct drm_plane *plane)
> >   }
> >   EXPORT_SYMBOL(drm_plane_create_alpha_property);
> >   
> > +static const struct drm_prop_enum_list rotation_props[] = {
> > +	{ __builtin_ffs(DRM_MODE_ROTATE_0) - 1,   "rotate-0" },
> > +	{ __builtin_ffs(DRM_MODE_ROTATE_90) - 1,  "rotate-90" },
> > +	{ __builtin_ffs(DRM_MODE_ROTATE_180) - 1, "rotate-180" },
> > +	{ __builtin_ffs(DRM_MODE_ROTATE_270) - 1, "rotate-270" },
> > +	{ __builtin_ffs(DRM_MODE_REFLECT_X) - 1,  "reflect-x" },
> > +	{ __builtin_ffs(DRM_MODE_REFLECT_Y) - 1,  "reflect-y" },
> > +};
> > +
> > +/**
> > + * drm_get_rotation_name - Return the name of a rotation
> > + * @rotation: The rotation mask (DRM_MODE_ROTATE_* | DRM_MODE_REFLECT_*)
> > + *
> > + * Returns: the name of the rotation type (unknown) if rotation is not
> > + * a known rotation/reflection
> > + */
> > +const char *drm_get_rotation_name(unsigned int rotation)
> > +{
> > +	if (rotation < ARRAY_SIZE(rotation_props))
> > +		return rotation_props[rotation].name;
>
> The value is a bitmask. This does not work.

That true, the documentation is not clear.

Take a look at patch 15 [1] for the usage. Is it better if I change the 
documentation to:

drm_get_rotation_name - Returns the name of a rotation/reflection 
bitmask (with only one bit set).
@rotation: Bitmask with a single bit set.
Name of the rotation/reflection, or "(unknown)" if invalid.

[1]:https://lore.kernel.org/all/20260422-vkms-all-config-v4-15-dbb52e9aadc3@xxxxxxxxxxx/