drm/i915/gt: Prevent allocation on a banned context

If a context is banned even before we submit our first request to it,
report the failure before we attempt to allocate any resources for the
context.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200303080546.1140508-2-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gt/intel_context.c

@@ -51,6 +51,11 @@ int intel_context_alloc_state(struct intel_context *ce)
 		return -EINTR;
 
 	if (!test_bit(CONTEXT_ALLOC_BIT, &ce->flags)) {
+		if (intel_context_is_banned(ce)) {
+			err = -EIO;
+			goto unlock;
+		}
+
 		err = ce->ops->alloc(ce);
 		if (unlikely(err))
 			goto unlock;