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

[Chris Wilson]

On Tue, Dec 17, 2013 at 02:02:23PM -0800, Ben Widawsky wrote:
> On Tue, Dec 17, 2013 at 07:24:41PM +0000, Chris Wilson wrote:
> > 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
> > 
> 
> 
> It should still check the module parameter - I guess it would be nice to
> guard changing the module parameter with struct_mutex (generally, not
> just here), as that also breaks the emit path.
> 
> So in short, I think it's broken for two reasons.
> 
> My (and Daniel's) vote is to just make the module param static.

Dynamic i915.semaphores is something I can live happily without. If we
ever do need such a thing, it needs to be internal to the kernel.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre