drm/vc4: Verify at boot that CMA doesn't cross a 256MB boundary.

I've seen lots of users cranking CMA up higher, so throw an error if
they do.

Signed-off-by: Eric Anholt <eric@anholt.net>

drivers/base/dma-contiguous.c

@@ -35,6 +35,7 @@
 #endif
 
 struct cma *dma_contiguous_default_area;
+EXPORT_SYMBOL(dma_contiguous_default_area);
 
 /*
  * Default global CMA area size can be defined in kernel's .config.

drivers/gpu/drm/vc4/vc4_v3d.c

@@ -16,7 +16,10 @@
  * this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+#include "linux/init.h"
+#include "linux/cma.h"
 #include "linux/component.h"
+#include "linux/dma-contiguous.h"
 #include "linux/pm_runtime.h"
 #include "vc4_drv.h"
 #include "vc4_regs.h"
@@ -185,8 +188,23 @@ static int vc4_v3d_bind(struct device *dev, struct device *master, void *data)
 	struct drm_device *drm = dev_get_drvdata(master);
 	struct vc4_dev *vc4 = to_vc4_dev(drm);
 	struct vc4_v3d *v3d = NULL;
+	struct cma *cma;
 	int ret;
 
+	cma = dev_get_cma_area(dev);
+	if (!cma)
+		return -EINVAL;
+
+	if ((cma_get_base(cma) & 0xf0000000) !=
+	    ((cma_get_base(cma) + cma_get_size(cma) - 1) & 0xf0000000)) {
+		DRM_ERROR("V3D requires that the CMA area (0x%08lx - 0x%08lx) "
+			  "not span a 256MB boundary, or memory corruption "
+			  "would happen.\n",
+			  (long)cma_get_base(cma),
+			  cma_get_base(cma) + cma_get_size(cma));
+		return -EINVAL;
+	}
+
 	v3d = devm_kzalloc(&pdev->dev, sizeof(*v3d), GFP_KERNEL);
 	if (!v3d)
 		return -ENOMEM;

mm/cma.c

@@ -47,11 +47,13 @@ phys_addr_t cma_get_base(const struct cma *cma)
 {
 	return PFN_PHYS(cma->base_pfn);
 }
+EXPORT_SYMBOL(cma_get_base);
 
 unsigned long cma_get_size(const struct cma *cma)
 {
 	return cma->count << PAGE_SHIFT;
 }
+EXPORT_SYMBOL(cma_get_size);
 
 static unsigned long cma_bitmap_aligned_mask(const struct cma *cma,
 					     int align_order)