linux/drivers/gpu/drm/i915/i915_user_extensions.h

/*
 * SPDX-License-Identifier: MIT
 *
 * Copyright © 2018 Intel Corporation
 */

#ifndef I915_USER_EXTENSIONS_H
#define I915_USER_EXTENSIONS_H

struct i915_user_extension;

typedef int (*i915_user_extension_fn)(struct i915_user_extension __user *ext,
				      void *data);

int i915_user_extensions(struct i915_user_extension __user *ext,
			 const i915_user_extension_fn *tbl,
			 unsigned int count,
			 void *data);

#endif /* I915_USER_EXTENSIONS_H */
drm/i915: Introduce the i915_user_extension_method 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 2019-03-22 09:23:22 +00:00			`/*`
			`* SPDX-License-Identifier: MIT`
			`*`
			`* Copyright © 2018 Intel Corporation`
			`*/`

			`#ifndef I915_USER_EXTENSIONS_H`
			`#define I915_USER_EXTENSIONS_H`

			`struct i915_user_extension;`

			`typedef int (i915_user_extension_fn)(struct i915_user_extension __user ext,`
			`void *data);`

			`int i915_user_extensions(struct i915_user_extension __user *ext,`
			`const i915_user_extension_fn *tbl,`
			`unsigned int count,`
			`void *data);`

			`#endif /* I915_USER_EXTENSIONS_H */`