[Intel-gfx] [PATCH v2 4/4] drm/i915/uapi: convert i915_query and friend to kernel doc

Matthew Auld
2021-04-19T10:59:14Z

Add a note about the two-step process.

v2(Tvrtko):
- Also document the other method of just passing in a buffer which is
large enough, which avoids two ioctl calls. Can make sense for
smaller query items.
v3: prefer kernel-doc references for structs and members

Suggested-by: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Kenneth Graunke <kenneth@whitecape.org>
Cc: Jason Ekstrand <jason@jlekstrand.net>
Cc: Dave Airlie <airlied@gmail.com>
Cc: dri-devel@lists.freedesktop.org
Cc: mesa-dev@lists.freedesktop.org
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
---
include/uapi/drm/i915_drm.h | 69 +++++++++++++++++++++++++++++--------
1 file changed, 55 insertions(+), 14 deletions(-)

diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index e2867d8cd5e3..6a34243a7646 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -2218,53 +2218,94 @@ struct drm_i915_perf_oa_config {
__u64 flex_regs_ptr;
};

+/**
+ * struct drm_i915_query_item - An individual query for the kernel to process.
+ *
+ * The behaviour is determined by the @query_id. Note that exactly what
+ * @data_ptr is also depends on the specific @query_id.
+ */
struct drm_i915_query_item {
+ /** @query_id: The id for this query */
__u64 query_id;
#define DRM_I915_QUERY_TOPOLOGY_INFO 1
#define DRM_I915_QUERY_ENGINE_INFO 2
#define DRM_I915_QUERY_PERF_CONFIG 3
/* Must be kept compact -- no holes and well documented */

- /*
+ /**
+ * @length:
+ *
* When set to zero by userspace, this is filled with the size of the
- * data to be written at the data_ptr pointer. The kernel sets this
+ * data to be written at the @data_ptr pointer. The kernel sets this
* value to a negative value to signal an error on a particular query
* item.
*/
__s32 length;

- /*
+ /**
+ * @flags:
+ *
* When query_id == DRM_I915_QUERY_TOPOLOGY_INFO, must be 0.
*
* When query_id == DRM_I915_QUERY_PERF_CONFIG, must be one of the
- * following :
- * - DRM_I915_QUERY_PERF_CONFIG_LIST
- * - DRM_I915_QUERY_PERF_CONFIG_DATA_FOR_UUID
- * - DRM_I915_QUERY_PERF_CONFIG_FOR_UUID
+ * following:
+ *
+ * - DRM_I915_QUERY_PERF_CONFIG_LIST
+ * - DRM_I915_QUERY_PERF_CONFIG_DATA_FOR_UUID
+ * - DRM_I915_QUERY_PERF_CONFIG_FOR_UUID
*/
__u32 flags;
#define DRM_I915_QUERY_PERF_CONFIG_LIST 1
#define DRM_I915_QUERY_PERF_CONFIG_DATA_FOR_UUID 2
#define DRM_I915_QUERY_PERF_CONFIG_DATA_FOR_ID 3

- /*
- * Data will be written at the location pointed by data_ptr when the
- * value of length matches the length of the data to be written by the
+ /**
+ * @data_ptr:
+ *
+ * Data will be written at the location pointed by @data_ptr when the
+ * value of @length matches the length of the data to be written by the
* kernel.
*/
__u64 data_ptr;
};

+/**
+ * struct drm_i915_query - Supply an array of struct drm_i915_query_item for the
+ * kernel to fill out.
+ *
+ * Note that this is generally a two step process for each struct
+ * drm_i915_query_item in the array:
+ *
+ * 1. Call the DRM_IOCTL_I915_QUERY, giving it our array of struct
+ * drm_i915_query_item, with &drm_i915_query_item.length set to zero. The
+ * kernel will then fill in the size, in bytes, which tells userspace how
+ * memory it needs to allocate for the blob(say for an array of properties).
+ *
+ * 2. Next we call DRM_IOCTL_I915_QUERY again, this time with the
+ * &drm_i915_query_item.data_ptr equal to our newly allocated blob. Note that
+ * the &drm_i915_query_item.length should still be the same as what the
+ * kernel previously set. At this point the kernel can fill in the blob.
+ *
+ * Note that for some query items it can make sense for userspace to just pass
+ * in a buffer/blob equal to or larger than the required size. In this case only
+ * a single ioctl call is needed. For some smaller query items this can work
+ * quite well.
+ *
+ */
struct drm_i915_query {
+ /** @num_items: The number of elements in the @items_ptr array */
__u32 num_items;

- /*
- * Unused for now. Must be cleared to zero.
+ /**
+ * @flags: Unused for now. Must be cleared to zero.
*/
__u32 flags;

- /*
- * This points to an array of num_items drm_i915_query_item structures.
+ /**
+ * @items_ptr:
+ *
+ * Pointer to an array of struct drm_i915_query_item. The number of
+ * array elements is @num_items.
*/
__u64 items_ptr;
};