Re: [PATCH i-g-t 1/2] lib/i915: Add helper for copying engine maps from one context to another

[Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>]

Quoting Tvrtko Ursulin (2020-01-24 12:17:58)
> From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> 
> We also need to support copying across file descriptors.
> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Sreedhar Telukuntla <sreedhar.telukuntla@xxxxxxxxx>
> ---
>  lib/i915/gem_context.c | 30 ++++++++++++++++++++++++++++++
>  lib/i915/gem_context.h |  2 ++
>  2 files changed, 32 insertions(+)
> 
> diff --git a/lib/i915/gem_context.c b/lib/i915/gem_context.c
> index 0b6a554dfe27..41957b66ca52 100644
> --- a/lib/i915/gem_context.c
> +++ b/lib/i915/gem_context.c
> @@ -462,3 +462,33 @@ bool gem_context_has_engine(int fd, uint32_t ctx, uint64_t engine)
>  
>         return __gem_execbuf(fd, &execbuf) == -ENOENT;
>  }
> +
> +/**
> + * gem_context_copy_engines:
> + * @src_fd: open i915 drm file descriptor where @src context belongs to
> + * @src: source engine map context id
> + * @dst_fd: open i915 drm file descriptor where @dst context belongs to
> + * @dst: destination engine map context id
> + *
> + * Special purpose wrapper for copying engine map from one context to another.
> + *
> + * In can be called regardless of whether the kernel supports context engine
> + * maps and is a no-op if not supported.
> + */
> +void
> +gem_context_copy_engines(int src_fd, uint32_t src, int dst_fd, uint32_t dst)
> +{
> +       I915_DEFINE_CONTEXT_PARAM_ENGINES(engines, I915_EXEC_RING_MASK + 1);
> +       struct drm_i915_gem_context_param param = {
> +               .param = I915_CONTEXT_PARAM_ENGINES,
> +               .ctx_id = src,
> +               .size = sizeof(engines),
> +               .value = to_user_pointer(&engines),
> +       };
> +
> +       if (__gem_context_get_param(src_fd, &param) || !param.size)
> +               return;
> +
> +       param.ctx_id = dst;
> +       gem_context_set_param(dst_fd, &param);

You don't want to copy across the use-default set? You presume dst is
already using defaults?
-Chris
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