[PATCH 9/9] drm/ttm: Sanity check mapping attributes on powerpc in ttm_io_prot()

[Benjamin Herrenschmidt]

On all current cache coherent powerpc processors, it is not legit
to map system memory non-cachable. This will cause aliases with
the linear mapping which can be fatal.

The TTM should generally avoid it after Jerome placement patches but
let's add a sanity check anyway to catch any possible remaining issue.

Signed-off-by: Benjamin Herrenschmidt <benh at palm4.ozlabs.ibm.com>
---
 drivers/gpu/drm/ttm/ttm_bo_util.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
index ef2ac3c..48095be 100644
--- a/drivers/gpu/drm/ttm/ttm_bo_util.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
@@ -37,6 +37,9 @@
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
 #include <linux/module.h>
+#if defined(__powerpc__)
+#include <asm/machdep.h>
+#endif
 
 void ttm_bo_free_old_node(struct ttm_buffer_object *bo)
 {
@@ -498,6 +501,20 @@ pgprot_t ttm_io_prot(uint32_t caching_flags, pgprot_t tmp)
 		tmp = pgprot_noncached(tmp);
 
 #endif
+#if defined(__powerpc__) && !defined(CONFIG_NOT_COHERENT_CACHE)
+	/*
+	 * Using a non-cachable mapping of system memory on
+	 * cache coherent powerpc's can be fatal, let's make
+	 * sure this doesn't happen and warn if it does. The
+	 * only exception is powermac with AGP which has to
+	 * take the risk.
+	 */
+	if (!machine_is(powermac) &&
+	    ((caching_flags & TTM_PL_FLAG_SYSTEM) ||
+	     (caching_flags & TTM_PL_FLAG_TT))) {
+		pr_err_once("TTM: Attempt to use a non-cached"
+			    " mapping on RAM unsupported !\n");
+		return tmp;
 	}
 #endif
 #if defined(__ia64__) || defined(__arm__) || defined(__powerpc__)