[Intel-gfx] [PATCH 02/15] drm/i915: Don't emit mbox updates without semaphores

[Chris Wilson]

On Mon, Dec 16, 2013 at 08:50:38PM -0800, Ben Widawsky wrote:
> Aside from the fact that it leaves confusing dumps on error capture, it
> is entirely unnecessary, and potentially harmful in cases like BDW,
> where the instruction has changed.
> 
> In reality (seemingly), this will have no behavioral impact.
> 
> Signed-off-by: Ben Widawsky <ben at bwidawsk.net>

The reason why we currently do is because i915.semaphores can change at
runtime. So we emit the instructions whilst i915.semaphores=0 just in
case, it is enabled later. This restriction can be lifted with a little
more work in handling the missed semaphores, I think, or it may just
require a proof that everything is safe as is.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre