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

[Louis Chauvet <louis.chauvet@bootlin.com>]

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/