[Intel-gfx] [PATCH 3/3] drm/i915/userptr: Enable read-only support on gen8+

[Chris Wilson]

On gen8 and onwards, we can mark GPU accesses through the ppGTT as being
read-only, that is cause any GPU write onto that page to be discarded
(not triggering a fault). This is all that we need to finally support
the read-only flag for userptr!

Testcase: igt/gem_userptr_blits/readonly*
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Jon Bloomfield <jon.bloomfield at intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
---
 drivers/gpu/drm/i915/i915_gem_userptr.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
index 854bd51b9478..d4ee8fa4c379 100644
--- a/drivers/gpu/drm/i915/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
@@ -789,10 +789,12 @@ i915_gem_userptr_ioctl(struct drm_device *dev,
 		return -EFAULT;
 
 	if (args->flags & I915_USERPTR_READ_ONLY) {
-		/* On almost all of the current hw, we cannot tell the GPU that a
-		 * page is readonly, so this is just a placeholder in the uAPI.
+		/*
+		 * On almost all of the older hw, we cannot tell the GPU that
+		 * a page is readonly.
 		 */
-		return -ENODEV;
+		if (INTEL_GEN(dev_priv) < 8 || !USES_PPGTT(dev_priv))
+			return -ENODEV;
 	}
 
 	obj = i915_gem_object_alloc(dev_priv);
@@ -806,7 +808,10 @@ i915_gem_userptr_ioctl(struct drm_device *dev,
 	i915_gem_object_set_cache_coherency(obj, I915_CACHE_LLC);
 
 	obj->userptr.ptr = args->user_ptr;
-	obj->userptr.read_only = !!(args->flags & I915_USERPTR_READ_ONLY);
+	if (args->flags & I915_USERPTR_READ_ONLY) {
+		obj->userptr.read_only = true;
+		obj->gt_ro = true;
+	}
 
 	/* And keep a pointer to the current->mm for resolving the user pages
 	 * at binding. This means that we need to hook into the mmu_notifier
-- 
2.17.0