Re: [PATCH 2/4] drm/i915: Introduce DRM_I915_GEM_MMAP_OFFSET

[Chris Wilson <chris@chris-wilson.co.uk>]

Quoting Abdiel Janulgue (2019-11-15 11:45:47)
> diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
> index 5400d7e057f1..e844c3a8d197 100644
> --- a/include/uapi/drm/i915_drm.h
> +++ b/include/uapi/drm/i915_drm.h
> @@ -395,6 +395,7 @@ typedef struct _drm_i915_sarea {
>  #define DRM_IOCTL_I915_GEM_PWRITE      DRM_IOW (DRM_COMMAND_BASE + DRM_I915_GEM_PWRITE, struct drm_i915_gem_pwrite)
>  #define DRM_IOCTL_I915_GEM_MMAP                DRM_IOWR(DRM_COMMAND_BASE + DRM_I915_GEM_MMAP, struct drm_i915_gem_mmap)
>  #define DRM_IOCTL_I915_GEM_MMAP_GTT    DRM_IOWR(DRM_COMMAND_BASE + DRM_I915_GEM_MMAP_GTT, struct drm_i915_gem_mmap_gtt)
> +#define DRM_IOCTL_I915_GEM_MMAP_OFFSET DRM_IOWR(DRM_COMMAND_BASE + DRM_I915_GEM_MMAP_GTT, struct drm_i915_gem_mmap_offset)
>  #define DRM_IOCTL_I915_GEM_SET_DOMAIN  DRM_IOW (DRM_COMMAND_BASE + DRM_I915_GEM_SET_DOMAIN, struct drm_i915_gem_set_domain)
>  #define DRM_IOCTL_I915_GEM_SW_FINISH   DRM_IOW (DRM_COMMAND_BASE + DRM_I915_GEM_SW_FINISH, struct drm_i915_gem_sw_finish)
>  #define DRM_IOCTL_I915_GEM_SET_TILING  DRM_IOWR (DRM_COMMAND_BASE + DRM_I915_GEM_SET_TILING, struct drm_i915_gem_set_tiling)
> @@ -793,6 +794,32 @@ struct drm_i915_gem_mmap_gtt {
>         __u64 offset;
>  };
>  
> +struct drm_i915_gem_mmap_offset {
> +       /** Handle for the object being mapped. */
> +       __u32 handle;
> +       __u32 pad;
> +       /**
> +        * Fake offset to use for subsequent mmap call
> +        *
> +        * This is a fixed-size type for 32/64 compatibility.
> +        */
> +       __u64 offset;
> +
> +       /**
> +        * Flags for extended behaviour.
> +        *
> +        * It is mandatory that either one of the MMAP_OFFSET flags
> +        * should be passed here.
> +        */
> +       __u64 flags;
> +#define I915_MMAP_OFFSET_GTT 0
> +#define I915_MMAP_OFFSET_WC  1
> +#define I915_MMAP_OFFSET_WB  2
> +#define I915_MMAP_OFFSET_UC  3

The only question left here is should we

#define I915_MMAP_USE_EXTENSIONS (1 << 8)

from the start and add the dummy user extension handler to ease
adaption.

Otherwise the uABI looks correct; though it merits doing something like

struct drm_i915_gem_mmap_gtt arg = { valid state };
u64 redzone[16];

memset(redzone, 0xc5, sizeof(redzone));
igt_assert_eq(ioctl(I915_GEM_MMAP_GTT, &arg), 0);

as that would have failed with the earlier patch. A useful exercise to
work through to make sure you understand why.

Please write that igt asap.
-Chris
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