[Intel-gfx] [PATCH] drm/i915: set ctx->initialized only after RCS

[Chris Wilson]

On Mon, Dec 30, 2013 at 01:34:46PM -0800, Ben Widawsky wrote:
> On Sun, Dec 29, 2013 at 09:59:26AM +0000, Chris Wilson wrote:
> > On Sat, Dec 28, 2013 at 01:31:49PM -0800, Ben Widawsky wrote:
> > > The initialized flag is used to specify a context has been initialized
> > > and it's context is safe to load, ie. the 3d state is setup properly.
> > > With full PPGTT, we emit the address space loads during context switch
> > > and this currently marks a context as initialized. With full PPGTT
> > > patches, if a client first emits a batch to !RCS, then later, RCS, the
> > > code will mistake the context as initialized and try to reload an
> > > uninitialized context.
> > > 
> > > 1. context 1 blit // context initialized
> > +context marked as initialised
> > 
> > > 2. context 2 <X operation> // saves context 1 random state
> > > 3. context 1 render // loads random state from step 2
> > 
> > Note that step 2 is not required since the tracking is per-ring.
> >  
> 
> This is missing an extremely important caveat which I was
> incorrectly correlating earlier in our discussion. Yes, step 2 is not
> required.  The step which is required is the page allocated must be
> non-zero when allocated, and the contents of the page must be capable of
> hanging the GPU when used as a context object.

Really? I'm pretty sure the last error state we looked at, the context
was all zeroes.
 
> Otherwise, the uninitialized context would always be all 0, which if I
> understand the HW correctly, is "safe"
> 
> As long as you don't disagree, I'll fix the commit message with that
> info.

Whatever you feel matches our best understanding of the problem. Just
double check that last error state first ;-)
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre