drm/i915/uapi: convert i915_query and friend to kernel doc

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>
Link: https://patchwork.freedesktop.org/patch/msgid/20210419105741.27844-4-matthew.auld@intel.com

diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index e2867d8cd5e30e5ab1ed93a1d39ef3980f35fd91..6a34243a7646acfed3cbcf42a5e55899c30606ee 100644 (file)
--- 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;
 };