[Intel-gfx] [PATCH] drm/i915: Codify our assumption that the Global GTT is <= 4GiB

[Chris Wilson]

Throughout the code base, we use u32 for offsets into the global GTT. If
we ever see any hardware with a larger GGTT, then we run the real risk
of silent corruption. So test for our assumption up front so that we
have a nice reminder should the time come when it fails.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Cc: Daniel Vetter <daniel at ffwll.ch>
---
 drivers/gpu/drm/i915/i915_gem_gtt.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
index 2e460b369e82..0d910638972c 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -3143,6 +3143,13 @@ int i915_gem_gtt_init(struct drm_device *dev)
 	if (ret)
 		return ret;
 
+	if ((gtt->base.total - 1) >> 32) {
+		DRM_ERROR("We never expected a Global GTT with more than 32bits of address space! Found %lldM!\n",
+			  gtt->base.total >> 20);
+		gtt->base.total = 1ull << 32;
+		gtt->mappable_end = min(gtt->mappable_end, gtt->base.total);
+	}
+
 	/* GMADR is the PCI mmio aperture into the global GTT. */
 	DRM_INFO("Memory usable by graphics device = %lluM\n",
 		 gtt->base.total >> 20);
-- 
2.7.0.rc3