[PATCH] drm/doc: Document ioctl errno value patterns

[Chris Wilson]

Quoting Daniel Vetter (2017-08-18 10:21:24)
> We're not super-consistent about these, but I think it's worth to
> document at least the commmon patterns.
> 
> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: "Zhang, Tina" <tina.zhang at intel.com>
> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>

One extra used outside of i915 is ENOSYS. Perhaps nouveau/vmgfx might
like to chime in if that's exposed to userspace and is a good pattern
you'ld like DRM as a whole to pick up.

As far as i915, these do capture our uses very well.
Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>

> ---
>  Documentation/gpu/drm-uapi.rst | 53 ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 53 insertions(+)
> 
> diff --git a/Documentation/gpu/drm-uapi.rst b/Documentation/gpu/drm-uapi.rst
> index 679373b4a03f..f3cc829467b4 100644
> --- a/Documentation/gpu/drm-uapi.rst
> +++ b/Documentation/gpu/drm-uapi.rst
> @@ -177,6 +177,59 @@ IOCTL Support on Device Nodes
>  .. kernel-doc:: drivers/gpu/drm/drm_ioc32.c
>     :export:
>  
> +Recommended IOCTL Return Values
> +===============================

Would this not be a preface to @drm_driver.ioctl() ?
-Chris