Re: [PATCH v3 2/4] drm/i915/uapi: convert i915_user_extension to kernel doc

From: Daniel Vetter <daniel@ffwll.ch>
To: Matthew Auld <matthew.auld@intel.com>
Cc: Jason Ekstrand <jason@jlekstrand.net>,
	Jordan Justen <jordan.l.justen@intel.com>,
	intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
	Kenneth Graunke <kenneth@whitecape.org>,
	mesa-dev@lists.freedesktop.org,
	Daniel Vetter <daniel.vetter@intel.com>
Subject: Re: [PATCH v3 2/4] drm/i915/uapi: convert i915_user_extension to kernel doc
Date: Fri, 16 Apr 2021 10:46:24 +0200	[thread overview]
Message-ID: <YHlO4CK8NjVtbSuS@phenom.ffwll.local> (raw)
In-Reply-To: <20210415155958.391624-2-matthew.auld@intel.com>

On Thu, Apr 15, 2021 at 04:59:56PM +0100, Matthew Auld wrote:
> Add some example usage for the extension chaining also, which is quite
> nifty.
> 
> 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: 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
> ---
>  include/uapi/drm/i915_drm.h | 46 +++++++++++++++++++++++++++++++++----
>  1 file changed, 42 insertions(+), 4 deletions(-)
> 
> diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
> index a50257cde9ff..d9c954a5a456 100644
> --- a/include/uapi/drm/i915_drm.h
> +++ b/include/uapi/drm/i915_drm.h
> @@ -62,8 +62,8 @@ extern "C" {
>  #define I915_ERROR_UEVENT		"ERROR"
>  #define I915_RESET_UEVENT		"RESET"
>  
> -/*
> - * i915_user_extension: Base class for defining a chain of extensions
> +/**
> + * struct i915_user_extension - Base class for defining a chain of extensions
>   *
>   * Many interfaces need to grow over time. In most cases we can simply
>   * extend the struct and have userspace pass in more data. Another option,
> @@ -76,12 +76,50 @@ extern "C" {
>   * increasing complexity, and for large parts of that interface to be
>   * entirely optional. The downside is more pointer chasing; chasing across
>   * the __user boundary with pointers encapsulated inside u64.
> + *
> + * Example chaining:
> + *
> + * .. code-block:: C
> + *
> + *	struct i915_user_extension ext3 {
> + *		.next_extension = 0, // end
> + *		.name = ...,
> + *	};
> + *	struct i915_user_extension ext2 {
> + *		.next_extension = (uintptr_t)&ext3,
> + *		.name = ...,
> + *	};
> + *	struct i915_user_extension ext1 {
> + *		.next_extension = (uintptr_t)&ext2,
> + *		.name = ...,
> + *	};
> + *
> + * Typically the i915_user_extension would be embedded in some uAPI struct, and
> + * in this case we would feed it the head of the chain(i.e ext1), which would
> + * then apply all of the above extensions.
> + *
>   */
>  struct i915_user_extension {
> +	/**
> +	 * @next_extension:
> +	 *
> +	 * Pointer to the next i915_user_extension, or zero if the end.
> +	 */
>  	__u64 next_extension;
> +	/** @name: Name of the extension */

Maybe clarify that the namespace here is per ioctl, not global. And maybe
also that the name is just an integer #define or something like that.

Either this is solid documentation, either way:

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

>  	__u32 name;
> -	__u32 flags; /* All undefined bits must be zero. */
> -	__u32 rsvd[4]; /* Reserved for future use; must be zero. */
> +	/**
> +	 * @flags: MBZ
> +	 *
> +	 * All undefined bits must be zero.
> +	 */
> +	__u32 flags;
> +	/**
> +	 * @rsvd: MBZ
> +	 *
> +	 * Reserved for future use; must be zero.
> +	 */
> +	__u32 rsvd[4];
>  };
>  
>  /*
> -- 
> 2.26.3
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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