Re: [PATCH v2] drm/i915: use semaphores for the display plane

[Chris Wilson <chris@chris-wilson.co.uk>]

On Thu,  5 Apr 2012 14:47:36 -0700, Ben Widawsky <ben@bwidawsk.net> wrote:
> In theory this will have performance and power improvements. Performance
> because we don't need to stall when the scanout BO is busy, and power
> because we don't have to stall when the BO is busy (and the ring can
> even go to sleep if the HW supports it).
> 
> v2:
> squash 2 patches into 1 (me)
> un-inline the enable_semaphores function (Daniel)
> remove comment about SNB hangs from i915_gem_object_sync (Chris)
> rename intel_enable_semaphores to i915_semaphore_is_enabled (me)
> removed page flip comment; "no why" (Chris)
> 
> To address other comments from Daniel (irc):
> update the comment to say 'vt-d is crap, don't enable semaphores'
>   - I think you misinterpreted Chris' comment, it already exists.
> checking out whether we can pageflip on the render ring on ivb (didn't
> work on early silicon)
>   - We don't want to enable workarounds for early silicon unless we have
>     to.
>   - I can't find any references in the docs about this.
> optionally use it if the fb is already busy on the render ring
>   - This should be how the code already worked, unless I am
>     misunderstanding your meaning.
> 
> CC: Chris Wilson <chris@chris-wilson.co.uk>
> Signed-off-by: Ben Widawsky <ben@bwidawsk.net>

> +int
> +i915_gem_object_sync(struct drm_i915_gem_object *obj,
> +		     struct intel_ring_buffer *to)
> +{
> +	struct intel_ring_buffer *from = obj->ring;
> +	u32 seqno;
> +	int ret, idx;
> +
> +	if (from == NULL || to == from)
> +		return 0;
> +
> +	if (!i915_semaphore_is_enabled(obj->base.dev))
Bug^ :(
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre