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Chris Wilson 9d1305ef80 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 13:12:30 +00:00
arch ARM: SoC fixes for v5.0 2019-03-02 16:43:15 -08:00
block
certs
crypto
Documentation Merge drm/drm-next into drm-intel-next-queued 2019-03-11 13:09:20 +02:00
drivers drm/i915: Introduce the i915_user_extension_method 2019-03-22 13:12:30 +00:00
firmware
fs Merge branch 'akpm' (patches from Andrew) 2019-03-01 09:04:59 -08:00
include drm/i915: Introduce the i915_user_extension_method 2019-03-22 13:12:30 +00:00
init revert "initramfs: cleanup incomplete rootfs" 2019-02-21 09:00:59 -08:00
ipc
kernel bpf: fix sanitation rewrite in case of non-pointers 2019-03-01 21:24:08 -08:00
lib kasan: turn off asan-stack for clang-8 and earlier 2019-03-01 09:02:33 -08:00
LICENSES
mm Merge branch 'akpm' (patches from Andrew) 2019-03-01 09:04:59 -08:00
net net: sit: fix memory leak in sit_init_net() 2019-03-02 00:53:23 -08:00
samples
scripts kasan: turn off asan-stack for clang-8 and earlier 2019-03-01 09:02:33 -08:00
security Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-02-24 09:28:26 -08:00
sound Merge drm/drm-next into drm-intel-next-queued 2019-03-11 13:09:20 +02:00
tools selftests: fixes for UDP GRO 2019-03-01 11:24:00 -08:00
usr
virt kvm: properly check debugfs dentry before using it 2019-02-28 08:57:32 -08:00
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore
.mailmap
COPYING
CREDITS CREDITS/MAINTAINERS: Retire parisc-linux.org email domain 2019-02-21 20:16:10 +01:00
Kbuild
Kconfig
MAINTAINERS Linux 5.0 2019-03-04 12:02:55 +10:00
Makefile Linux 5.0 2019-03-03 15:21:29 -08:00
README

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.