[Intel-gfx] [PATCH v2] drm/i915: add register read IOCTL

[Eric Anholt]

Ben Widawsky <ben at bwidawsk.net> writes:

> The interface's immediate purpose is to do synchronous timestamp queries
> as required by GL_TIMESTAMP. The GPU has a register for reading the
> timestamp but because that would normally require root access through
> libpciaccess, the IOCTL can provide this service instead.
>
> Currently the implementation whitelists only the render ring timestamp
> register, because that is the only thing we need to expose at this time.
>
> v2: make size implicit based on the register offset
> Add a generation check

> diff --git a/include/drm/i915_drm.h b/include/drm/i915_drm.h
> index 8cc7083..fbe7757 100644
> --- a/include/drm/i915_drm.h
> +++ b/include/drm/i915_drm.h
> @@ -203,6 +203,7 @@ typedef struct _drm_i915_sarea {
>  #define DRM_I915_GEM_WAIT	0x2c
>  #define DRM_I915_GEM_CONTEXT_CREATE	0x2d
>  #define DRM_I915_GEM_CONTEXT_DESTROY	0x2e
> +#define DRM_I915_REG_READ	0x30

Is 0x2f some other outstanding ioctl?

Other than that,

Reviewed-by: Eric Anholt <eric at anholt.net>

Note: we have requests both by Arjan and by Valve for the functionality
that this patch will allow.
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