[PATCH] drm/radeon: handle broken disabled rb mask gracefully (6xx/7xx)

[Alex Deucher]

This is a port of cedb655a3a7764c3fd946077944383c9e0e68dd4
to older asics.  Fixes a possible divide by 0 if the harvest
register is invalid.

Signed-off-by: Alex Deucher <alexander.deucher at amd.com>
Cc: stable at vger.kernel.org
---
 drivers/gpu/drm/radeon/r600.c  | 8 ++++++++
 drivers/gpu/drm/radeon/rv770.c | 8 ++++++++
 2 files changed, 16 insertions(+)

diff --git a/drivers/gpu/drm/radeon/r600.c b/drivers/gpu/drm/radeon/r600.c
index e79d3f8..42d0564 100644
--- a/drivers/gpu/drm/radeon/r600.c
+++ b/drivers/gpu/drm/radeon/r600.c
@@ -2054,6 +2054,14 @@ static void r600_gpu_init(struct radeon_device *rdev)
 	rdev->config.r600.active_simds = tmp;
 
 	disabled_rb_mask = (RREG32(CC_RB_BACKEND_DISABLE) >> 16) & R6XX_MAX_BACKENDS_MASK;
+	tmp = 0;
+	for (i = 0; i < rdev->config.r600.max_backends; i++)
+		tmp |= (1 << i);
+	/* if all the backends are disabled, fix it up here */
+	if ((disabled_rb_mask & tmp) == tmp) {
+		for (i = 0; i < rdev->config.r600.max_backends; i++)
+			disabled_rb_mask &= ~(1 << i);
+	}
 	tmp = (tiling_config & PIPE_TILING__MASK) >> PIPE_TILING__SHIFT;
 	tmp = r6xx_remap_render_backend(rdev, tmp, rdev->config.r600.max_backends,
 					R6XX_MAX_BACKENDS, disabled_rb_mask);
diff --git a/drivers/gpu/drm/radeon/rv770.c b/drivers/gpu/drm/radeon/rv770.c
index 2983f17..340596a 100644
--- a/drivers/gpu/drm/radeon/rv770.c
+++ b/drivers/gpu/drm/radeon/rv770.c
@@ -1348,6 +1348,14 @@ static void rv770_gpu_init(struct radeon_device *rdev)
 	rdev->config.rv770.tiling_npipes = rdev->config.rv770.max_tile_pipes;
 
 	disabled_rb_mask = (RREG32(CC_RB_BACKEND_DISABLE) >> 16) & R7XX_MAX_BACKENDS_MASK;
+	tmp = 0;
+	for (i = 0; i < rdev->config.rv770.max_backends; i++)
+		tmp |= (1 << i);
+	/* if all the backends are disabled, fix it up here */
+	if ((disabled_rb_mask & tmp) == tmp) {
+		for (i = 0; i < rdev->config.rv770.max_backends; i++)
+			disabled_rb_mask &= ~(1 << i);
+	}
 	tmp = (gb_tiling_config & PIPE_TILING__MASK) >> PIPE_TILING__SHIFT;
 	tmp = r6xx_remap_render_backend(rdev, tmp, rdev->config.rv770.max_backends,
 					R7XX_MAX_BACKENDS, disabled_rb_mask);
-- 
1.8.3.1