[Intel-gfx] [PATCH 1/2] [v3] drm/i915: reference count for i915_hw_contexts

[Chris Wilson]

On Tue, Apr 02, 2013 at 06:27:00PM -0700, Ben Widawsky wrote:
> On Tue, Apr 02, 2013 at 03:45:42PM -0700, Ben Widawsky wrote:
> > From: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> > 
> > In preparation to do analysis of which context was
> > guilty of gpu hung, store kreffed context pointer
> > into request struct.
> > 
> > This allows us to inspect contexts when gpu is reset
> > even if those contexts would already be released
> > by userspace.
> > 
> > v2: track i915_hw_context pointers instead of using ctx_ids
> >     (from Chris Wilson)
> > 
> > v3 (Ben): Get rid of do_release() and handle refcounting more compactly.
> > (recommended by Chris)
> > 
> > Signed-off-by: Mika Kuoppala <mika.kuoppala at intel.com>
> > Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
> 
> Now I remember why my version of reference counting was so much more
> complicated. In my case, I want to keep the last context around instead
> of the last context object. To do this we can't do a kref_put until
> we've switched to the next context (similar to how we manage the context
> object). I want to do this since the context stores the PPGTT which will
> currently be in use. I need to switch PDEs at context switch time.

This seems feasible using requests and a callback from retire. The
alternative is something hairy like intel_overlay, hence my desire for
keeping all ring operations as a i915_gem_request.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre