[Mesa-dev] [Intel-gfx] [PATCH v3 3/4] drm/i915/uapi: convert i915_query and friend to kernel doc

[Tvrtko Ursulin]

On 15/04/2021 16:59, Matthew Auld wrote:
> Add a note about the two-step process.
> 
> Suggested-by: Daniel Vetter <daniel at ffwll.ch>
> Signed-off-by: Matthew Auld <matthew.auld at intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> Cc: Jordan Justen <jordan.l.justen at intel.com>
> Cc: Daniel Vetter <daniel.vetter at intel.com>
> Cc: Kenneth Graunke <kenneth at whitecape.org>
> Cc: Jason Ekstrand <jason at jlekstrand.net>
> Cc: Dave Airlie <airlied at gmail.com>
> Cc: dri-devel at lists.freedesktop.org
> Cc: mesa-dev at 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
> + * @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.

I'd also document the one step alternative where userspace passes in a 
buffer equal or larger than the required size. For many small queries 
(most?) this actually works just as well and with one ioctl only.

Regards,

Tvrtko

> + *
> + */
>   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;
>   };
>