On 4/15/21 8:59 AM, Matthew Auld wrote:
> Add a note about the two-step process.
> 
> Suggested-by: Daniel Vetter <dan...@ffwll.ch>
> Signed-off-by: Matthew Auld <matthew.a...@intel.com>
> Cc: Joonas Lahtinen <joonas.lahti...@linux.intel.com>
> Cc: Jordan Justen <jordan.l.jus...@intel.com>
> Cc: Daniel Vetter <daniel.vet...@intel.com>
> Cc: Kenneth Graunke <kenn...@whitecape.org>
> Cc: Jason Ekstrand <ja...@jlekstrand.net>
> Cc: Dave Airlie <airl...@gmail.com>
> Cc: dri-devel@lists.freedesktop.org
> Cc: mesa-...@lists.freedesktop.org
> ---
>  include/uapi/drm/i915_drm.h | 57 ++++++++++++++++++++++++++++++-------
>  1 file changed, 46 insertions(+), 11 deletions(-)
> 
> diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
> index d9c954a5a456..ef36f1a0adde 100644
> --- a/include/uapi/drm/i915_drm.h
> +++ b/include/uapi/drm/i915_drm.h
> @@ -2210,14 +2210,23 @@ 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

Since we just had a big discussion about this on mesa-dev w.r.t. Mesa
code and documentation... does the kernel have a policy about which
flavor (pun intended) of English should be used?

> + * @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
>        * value to a negative value to signal an error on a particular query
> @@ -2225,21 +2234,26 @@ struct drm_i915_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_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.
> @@ -2247,16 +2261,37 @@ struct drm_i915_query_item {
>       __u64 data_ptr;
>  };
>  
> +/**
> + * struct drm_i915_query - Supply an array of drm_i915_query_item for the 
> kernel
> + * to fill out.
> + *
> + * Note that this is generally a two step process for each 
> drm_i915_query_item
> + * in the array:
> + *
> + *   1.) Call the DRM_IOCTL_I915_QUERY, giving it our array of
> + *   drm_i915_query_item, with drm_i915_query_item.size 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 i915_query_item.size should still be the same as what the
> + *   kernel previously set. At this point the kernel can fill in the blob.
> + *
> + */
>  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: This points to an array of num_items drm_i915_query_item
> +      * structures.
>        */
>       __u64 items_ptr;
>  };
> 

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