Re: [PATCH 13/13] DONT_MERGE drm/i915: FORCE_RESTORE for gen8 semaphores

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

On Wed, Apr 30, 2014 at 11:44:47AM -0700, Ben Widawsky wrote:
> On Wed, Apr 30, 2014 at 08:13:25AM +0100, Chris Wilson wrote:
> > On Tue, Apr 29, 2014 at 02:52:40PM -0700, Ben Widawsky wrote:
> > > This appears to not actually be needed on the current code. Just putting
> > > it on the ML so we can point bug reports at it later.
> > > 
> > > As pointed out by Ville, the current code is "broken" since we do
> > > FORCE_RESTORE, and RESTORE_INHIBIT on the same dword. Anecdotally, this
> > > seems fine.
> > > 
> > > Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
> > > ---
> > >  drivers/gpu/drm/i915/i915_gem_context.c | 7 +++++++
> > >  1 file changed, 7 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
> > > index f77b4c1..aa82fb4 100644
> > > --- a/drivers/gpu/drm/i915/i915_gem_context.c
> > > +++ b/drivers/gpu/drm/i915/i915_gem_context.c
> > > @@ -661,6 +661,13 @@ static int do_switch(struct intel_ring_buffer *ring,
> > >  	if (!to->is_initialized || i915_gem_context_is_default(to))
> > >  		hw_flags |= MI_RESTORE_INHIBIT;
> > >  
> > > +	/* When SW intends to use semaphore signaling between Command streamers,
> > > +	 * it must avoid lite restores in HW by programming "Force Restore" bit
> > > +	 * to ‘1’ in context descriptor during context submission
> > > +	 */
> > > +	if (IS_GEN8(ring->dev) && i915_semaphore_is_enabled(ring->dev))
> > > +		hw_flags |= MI_FORCE_RESTORE;
> > 
> > Is it not an error to set both FORCE and INHIBIT?
> > -Chris
> 
> Read the commit message.

And for once I was reading the code. Wouldn't it be worth to clear
MI_RESTORE_INHIBIT any way to silence the critics?
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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