From b67e0a6a7409f9c1a12e573fb7d8d80ee455b103 Mon Sep 17 00:00:00 2001
From: Adam Jackson <ajax@redhat.com>
Date: Mon, 17 Jun 2013 09:59:34 -0400
Subject: [PATCH] drm/radeon: Disable writeback by default on ppc
 
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@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