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9d1305ef80
An idea for extending uABI inspired by Vulkan's extension chains.
Instead of expanding the data struct for each ioctl every time we need
to add a new feature, define an extension chain instead. As we add
optional interfaces to control the ioctl, we define a new extension
struct that can be linked into the ioctl data only when required by the
user. The key advantage being able to ignore large control structs for
optional interfaces/extensions, while being able to process them in a
consistent manner.
In comparison to other extensible ioctls, the key difference is the
use of a linked chain of extension structs vs an array of tagged
pointers. For example,
struct drm_amdgpu_cs_chunk {
__u32 chunk_id;
__u32 length_dw;
__u64 chunk_data;
};
struct drm_amdgpu_cs_in {
__u32 ctx_id;
__u32 bo_list_handle;
__u32 num_chunks;
__u32 _pad;
__u64 chunks;
};
allows userspace to pass in array of pointers to extension structs, but
must therefore keep constructing that array along side the command stream.
In dynamic situations like that, a linked list is preferred and does not
similar from extra cache line misses as the extension structs themselves
must still be loaded separate to the chunks array.
v2: Apply the tail call optimisation directly to nip the worry of stack
overflow in the bud.
v3: Defend against recursion.
v4: Fixup local types to match new uabi
Opens:
- do we include the result as an out-field in each chain?
struct i915_user_extension {
__u64 next_extension;
__u64 name;
__s32 result;
__u32 mbz; /* reserved for future use */
};
* Undecided, so provision some room for future expansion.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190322092325.5883-1-chris@chris-wilson.co.uk
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| .. | ||
| amdgpu_drm.h | ||
| armada_drm.h | ||
| drm.h | ||
| drm_fourcc.h | ||
| drm_mode.h | ||
| drm_sarea.h | ||
| etnaviv_drm.h | ||
| exynos_drm.h | ||
| i810_drm.h | ||
| i915_drm.h | ||
| mga_drm.h | ||
| msm_drm.h | ||
| nouveau_drm.h | ||
| omap_drm.h | ||
| qxl_drm.h | ||
| r128_drm.h | ||
| radeon_drm.h | ||
| savage_drm.h | ||
| sis_drm.h | ||
| tegra_drm.h | ||
| v3d_drm.h | ||
| vc4_drm.h | ||
| vgem_drm.h | ||
| via_drm.h | ||
| virtgpu_drm.h | ||
| vmwgfx_drm.h | ||