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

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Thu, Apr 23, 2026 at 10:47:38AM +0200, Louis Chauvet wrote:
> 
> 
> 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@redhat.com>
> >> Reviewed-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
> >> Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>
> >> ---
> >>   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@bootlin.com/

For that kind of local thing I don't think it should be called
drm_get_rotation_name(). Also your docs seem to disagree with the
implementation. 

But this does sound like a useful thing to have, eg. in
drm_atomic_plane_print_state().

We already have at least one implementation of this in
i915/display/intel_display_debugfs.c, although with a bit more
terse format (and with somewhat weird "FLIP" terminology) to
make it not eat so much screen real estate.

-- 
Ville Syrjälä
Intel