drm/i915: Avoid snooping with userptr where not supported

   commit e5756c10
   Author: Imre Deak <imre.deak@intel.com>
   Date:   Fri Aug 14 18:43:30 2015 +0300

       drm/i915/bxt: don't allow cached GEM mappings on A stepping

Added an exception of disallowing snooping for Broxton A
stepping hardware but userptr was still enabling it regardless.

Move the check to HAS_SNOOP now that it is used from multiple
call sites and use it.

v2: Userptr cannot be supported when it cannot be coherent and
    generalize the code better. (Chris Wilson)

v3: Make has_snoop true only when !has_llc. (Chris Wilson)
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Imre Deak <imre.deak@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1456920631-34302-1-git-send-email-tvrtko.ursulin@linux.intel.com

drivers/gpu/drm/i915/i915_dma.c

@@ -853,6 +853,10 @@ static void intel_device_info_runtime_init(struct drm_device *dev)
 	else if (INTEL_INFO(dev)->gen >= 9)
 		gen9_sseu_info_init(dev);
 
+	/* Snooping is broken on BXT A stepping. */
+	info->has_snoop = !info->has_llc;
+	info->has_snoop &= !IS_BXT_REVID(dev, 0, BXT_REVID_A1);
+
 	DRM_DEBUG_DRIVER("slice total: %u\n", info->slice_total);
 	DRM_DEBUG_DRIVER("subslice total: %u\n", info->subslice_total);
 	DRM_DEBUG_DRIVER("subslice per slice: %u\n", info->subslice_per_slice);

drivers/gpu/drm/i915/i915_drv.h

@@ -786,6 +786,7 @@ struct intel_csr {
 	func(overlay_needs_physical) sep \
 	func(supports_tv) sep \
 	func(has_llc) sep \
+	func(has_snoop) sep \
 	func(has_ddi) sep \
 	func(has_fpga_dbg)
 
@@ -2630,6 +2631,7 @@ struct drm_i915_cmd_table {
 #define HAS_BLT(dev)		(INTEL_INFO(dev)->ring_mask & BLT_RING)
 #define HAS_VEBOX(dev)		(INTEL_INFO(dev)->ring_mask & VEBOX_RING)
 #define HAS_LLC(dev)		(INTEL_INFO(dev)->has_llc)
+#define HAS_SNOOP(dev)		(INTEL_INFO(dev)->has_snoop)
 #define HAS_WT(dev)		((IS_HASWELL(dev) || IS_BROADWELL(dev)) && \
 				 __I915__(dev)->ellc_size)
 #define I915_NEED_GFX_HWS(dev)	(INTEL_INFO(dev)->need_gfx_hws)

drivers/gpu/drm/i915/i915_gem.c

@@ -3949,7 +3949,7 @@ int i915_gem_set_caching_ioctl(struct drm_device *dev, void *data,
 		 * cacheline, whereas normally such cachelines would get
 		 * invalidated.
 		 */
-		if (IS_BXT_REVID(dev, 0, BXT_REVID_A1))
+		if (!HAS_LLC(dev) && !HAS_SNOOP(dev))
 			return -ENODEV;
 
 		level = I915_CACHE_LLC;

drivers/gpu/drm/i915/i915_gem_userptr.c

@@ -758,6 +758,13 @@ i915_gem_userptr_ioctl(struct drm_device *dev, void *data, struct drm_file *file
 	int ret;
 	u32 handle;
 
+	if (!HAS_LLC(dev) && !HAS_SNOOP(dev)) {
+		/* We cannot support coherent userptr objects on hw without
+		 * LLC and broken snooping.
+		 */
+		return -ENODEV;
+	}
+
 	if (args->flags & ~(I915_USERPTR_READ_ONLY |
 			    I915_USERPTR_UNSYNCHRONIZED))
 		return -EINVAL;