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drm: document drm_mode_get_property

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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.

v2: document enum drm_mode_property_enum, add ref to "Modeset Base
Object Abstraction" (Daniel)

Signed-off-by: Simon Ser <contact@emersion.fr>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Leandro Ribeiro <leandro.ribeiro@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210802072826.500078-1-contact@emersion.fr
This commit is contained in:
Simon Ser 2021-08-02 07:28:35 +00:00
parent 2f425cf524
commit 6e5b47a4f1
2 changed files with 58 additions and 4 deletions
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2
Documentation/gpu/drm-kms.rst
View File

@ -159,6 +159,8 @@ KMS Core Structures and Functions
.. kernel-doc:: drivers/gpu/drm/drm_mode_config.c
:export:
.. _kms_base_object_abstraction:
Modeset Base Object Abstraction
===============================

60
include/uapi/drm/drm_mode.h
View File

@ -541,22 +541,74 @@ struct drm_mode_get_connector {
*/
#define DRM_MODE_PROP_ATOMIC 0x80000000
/**
* struct drm_mode_property_enum - Description for an enum/bitfield entry.
* @value: numeric value for this enum entry.
* @name: symbolic name for this enum entry.
*
* See struct drm_property_enum for details.
*/
struct drm_mode_property_enum {
__u64 value;
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 same property may be attached to multiple objects, see
* "Modeset Base Object Abstraction".
*
* 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.
*/
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. */
__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;
};