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

[Ben Widawsky]

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
2. context 2 <X operation> // saves context 1 random state
3. context 1 render // loads random state from step 2

It is really easy to hit this with a planned upcoming patch which makes
default context reuse possible.

NOTE: This should only effect full PPGTT branches, ie. current
drm-intel-nightly.

Thanks to Chris for helping me track this down.

Cc: Chris Wilson <chris at chris-wilson.co.uk>
Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
---
 drivers/gpu/drm/i915/i915_gem_context.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index ebe0f67..28b9f30 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -686,10 +686,11 @@ static int do_switch(struct intel_ring_buffer *ring,
 		i915_gem_context_unreference(from);
 	}
 
+	to->is_initialized = true;
+
 done:
 	i915_gem_context_reference(to);
 	ring->last_context = to;
-	to->is_initialized = true;
 	to->last_ring = ring;
 
 	return 0;
-- 
1.8.5.2