[PATCH] drm/radeon: Disable writeback by default on ppc

[Adam Jackson]

At least on an IBM Power 720, this check passes, but several piglit
tests will reliably trigger GPU resets due to the ring buffer pointers
not being updated.  There's probably a better way to limit this to just
affected machines though.

Signed-off-by: Adam Jackson <ajax at redhat.com>
---
 drivers/gpu/drm/radeon/r600_cp.c       | 7 +++++++
 drivers/gpu/drm/radeon/radeon_cp.c     | 7 +++++++
 drivers/gpu/drm/radeon/radeon_device.c | 4 ++--
 drivers/gpu/drm/radeon/radeon_drv.c    | 2 +-
 4 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/radeon/r600_cp.c b/drivers/gpu/drm/radeon/r600_cp.c
index 1c51c08..ef28532 100644
--- a/drivers/gpu/drm/radeon/r600_cp.c
+++ b/drivers/gpu/drm/radeon/r600_cp.c
@@ -552,6 +552,13 @@ static void r600_test_writeback(drm_radeon_private_t *dev_priv)
 		dev_priv->writeback_works = 0;
 		DRM_INFO("writeback test failed\n");
 	}
+#if defined(__ppc__) || defined(__ppc64__)
+	/* the test might succeed on ppc, but it's usually not reliable */
+	if (radeon_no_wb == -1) {
+		radeon_no_wb = 1;
+		DRM_INFO("not trusting writeback test due to arch quirk\n");
+	}
+#endif
 	if (radeon_no_wb == 1) {
 		dev_priv->writeback_works = 0;
 		DRM_INFO("writeback forced off\n");
diff --git a/drivers/gpu/drm/radeon/radeon_cp.c b/drivers/gpu/drm/radeon/radeon_cp.c
index efc4f64..a967b33 100644
--- a/drivers/gpu/drm/radeon/radeon_cp.c
+++ b/drivers/gpu/drm/radeon/radeon_cp.c
@@ -892,6 +892,13 @@ static void radeon_test_writeback(drm_radeon_private_t * dev_priv)
 		dev_priv->writeback_works = 0;
 		DRM_INFO("writeback test failed\n");
 	}
+#if defined(__ppc__) || defined(__ppc64__)
+	/* the test might succeed on ppc, but it's usually not reliable */
+	if (radeon_no_wb == -1) {
+		radeon_no_wb = 1;
+		DRM_INFO("not trusting writeback test due to arch quirk\n");
+	}
+#endif
 	if (radeon_no_wb == 1) {
 		dev_priv->writeback_works = 0;
 		DRM_INFO("writeback forced off\n");
diff --git a/drivers/gpu/drm/radeon/radeon_device.c b/drivers/gpu/drm/radeon/radeon_device.c
index 1899738..524046e 100644
--- a/drivers/gpu/drm/radeon/radeon_device.c
+++ b/drivers/gpu/drm/radeon/radeon_device.c
@@ -322,8 +322,8 @@ int radeon_wb_init(struct radeon_device *rdev)
 	/* disable event_write fences */
 	rdev->wb.use_event = false;
 	/* disabled via module param */
-	if (radeon_no_wb == 1) {
-		rdev->wb.enabled = false;
+	if (radeon_no_wb != -1) {
+		rdev->wb.enabled = !!radeon_no_wb;
 	} else {
 		if (rdev->flags & RADEON_IS_AGP) {
 			/* often unreliable on AGP */
diff --git a/drivers/gpu/drm/radeon/radeon_drv.c b/drivers/gpu/drm/radeon/radeon_drv.c
index 094e7e5..04809d4 100644
--- a/drivers/gpu/drm/radeon/radeon_drv.c
+++ b/drivers/gpu/drm/radeon/radeon_drv.c
@@ -146,7 +146,7 @@ static inline void radeon_register_atpx_handler(void) {}
 static inline void radeon_unregister_atpx_handler(void) {}
 #endif
 
-int radeon_no_wb;
+int radeon_no_wb = -1;
 int radeon_modeset = -1;
 int radeon_dynclks = -1;
 int radeon_r4xx_atom = 0;
-- 
1.8.2.1