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

[Ben Widawsky]

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.

-- 
Ben Widawsky, Intel Open Source Technology Center