On Wed, Jul 21, 2021 at 06:49:32AM +0000, Simon Ser wrote:
It's not obvious what the fields mean and how they should be used. The most important detail is the link to drm_property.flags, which describes how property types work.
Signed-off-by: Simon Ser contact@emersion.fr Cc: Pekka Paalanen pekka.paalanen@collabora.com Cc: Daniel Vetter daniel.vetter@ffwll.ch Cc: Leandro Ribeiro leandro.ribeiro@collabora.com
include/uapi/drm/drm_mode.h | 52 ++++++++++++++++++++++++++++++++++--- 1 file changed, 48 insertions(+), 4 deletions(-)
diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h index 98bf130feda5..dfdb595875aa 100644 --- a/include/uapi/drm/drm_mode.h +++ b/include/uapi/drm/drm_mode.h @@ -546,17 +546,61 @@ struct drm_mode_property_enum { char name[DRM_PROP_NAME_LEN]; };
+/**
- struct drm_mode_get_property - Get property metadata.
- User-space can perform a GETPROPERTY ioctl to retrieve information about a
- property.
- The meaning of the @values_ptr field changes depending on the property type.
- See &drm_property.flags for more details.
- The @enum_blob_ptr and @count_enum_blobs fields are only meaningful when the
- property has the type &DRM_MODE_PROP_ENUM or &DRM_MODE_PROP_BITMASK. For
- backwards compatibility, the kernel will always set @count_enum_blobs to
- zero when the property has the type &DRM_MODE_PROP_BLOB. User-space must
- ignore these two fields if the property has a different type.
- User-space is expected to retrieve values and enums by performing this ioctl
- at least twice: the first time to retrieve the number of elements, the
- second time to retrieve the elements themselves.
- To retrieve the number of elements, set @count_values and @count_enum_blobs
- to zero, then call the ioctl. @count_values will be updated with the number
- of elements. If the property has the type &DRM_MODE_PROP_ENUM or
- &DRM_MODE_PROP_BITMASK, @count_enum_blobs will be updated as well.
- To retrieve the elements themselves, allocate an array for @values_ptr and
- set @count_values to its capacity. If the property has the type
- &DRM_MODE_PROP_ENUM or &DRM_MODE_PROP_BITMASK, allocate an array for
- @enum_blob_ptr and set @count_enum_blobs to its capacity. Calling the ioctl
- again will fill the arrays.
I think it would be really good to link to
https://dri.freedesktop.org/docs/drm/gpu/drm-kms.html#modeset-base-object-ab...
for all the property related ioctl. That entire class vs instance confusion is pretty common I think, which is why I even made a nice picture about it :-)
- */
struct drm_mode_get_property {
- __u64 values_ptr; /* values and blob lengths */
- __u64 enum_blob_ptr; /* enum and blob id ptrs */
- /** @values_ptr: Pointer to a ``__u64`` array. */
- __u64 values_ptr;
- /** @enum_blob_ptr: Pointer to a struct drm_mode_property_enum array. */
I guess would be nice to also document that drm_mode_property_enum. Especially whether we also have this nice confusion between value and bitmask there too (I guess so).
__u64 enum_blob_ptr;
/**
* @prop_id: Object ID of the property which should be retrieved. Set* by the caller.*/__u32 prop_id;
/**
* @flags: ``DRM_MODE_PROP_*`` bitfield. See &drm_property.flags for* a definition of the flags.*/__u32 flags;
/**
* @name: Symbolic property name. User-space should use this field to* recognize properties.*/char name[DRM_PROP_NAME_LEN];
/** @count_values: Number of elements in @values_ptr. */ __u32 count_values;
- /* This is only used to count enum values, not blobs. The _blobs is
* simply because of a historical reason, i.e. backwards compat. */
- /** @count_enum_blobs: Number of elements in @enum_blob_ptr. */ __u32 count_enum_blobs;
Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch
};
-- 2.32.0