Re: [PATCH 18/38] drm/i915: Extend CONTEXT_CREATE to set parameters upon construction

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 01/03/2019 19:10, Chris Wilson wrote:
> Quoting Tvrtko Ursulin (2019-03-01 16:36:45)
>>
>> On 01/03/2019 14:03, Chris Wilson wrote:
>>> It can be useful to have a single ioctl to create a context with all
>>> the initial parameters instead of a series of create + setparam + setparam
>>> ioctls. This extension to create context allows any of the parameters
>>> to be passed in as a linked list to be applied to the newly constructed
>>> context.
>>>
>>> v2: Make a local copy of user setparam (Tvrtko)
>>> v3: Use flags to detect availability of extension interface
>>
>> Looks good to me.
>>
>> Why have you changed to use flags and not just check the extension field
>> being non-null?
> 
> Hmm. I was thinking about how new userspace would use it on an old kernel.
> As the extension is in a new bit of the extension struct that won't be
> passed to the old ioctl, and so it would create a context and not report
> any error despite not processing the extensions (userspace would be none
> the wiser that the context was invalid). So a simple answer was to use
> the flags field to indicate that we want the extension processed; the
> old kernel would reject the ioctl due to pad!=0, a new kernel will be
> happy. New userspace on old kernel can then fallback gracefully.
> 
> +uint32_t
> +brw_clone_hw_context(struct brw_bufmgr *bufmgr, uint32_t ctx_id)
> +{
> +   struct drm_i915_gem_context_create_ext_clone ext_clone = {
> +      .base = { I915_CONTEXT_CREATE_EXT_CLONE },
> +      .clone = ctx_id,
> +      .flags = ~I915_CONTEXT_CLONE_UNKNOWN,
> +   };
> +   struct drm_i915_gem_context_create_ext arg = {
> +      .flags = I915_CONTEXT_CREATE_USE_EXTENSIONS,
> +      .extensions = (uintptr_t)&ext_clone
> +   };
> +   if (drmIoctl(bufmgr->fd, DRM_IOCTL_I915_GEM_CONTEXT_CREATE_EXT, &arg) == 0)
> +      return arg.ctx_id;
> +
> +   return __brw_clone_hw_context(bufmgr, ctx_id);
> +}

Yeah, makes sense.

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko
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