drm/radeon/kms: check/restore sanity before doing anything else with GPU.

On systems using kexec, the new kernel is booted straight from the old kernel, without any warning to the graphics driver. So the GPU is basically left as-is in a running state, however the CPU side is completly reset.

Without stating the saneness of anyone using kexec on live systems, we should at least try not to crash the GPU. This patch resets 3 registers to 0 that could cause bad things to happen to the running system.

This allows kexec to work on a Power6/RN50 system.

Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 27 insertions, 0 deletions

diff --git a/drivers/gpu/drm/radeon/r100.c b/drivers/gpu/drm/radeon/r100.c
index 5aa299527317..5d14732dc284 100644
--- a/drivers/gpu/drm/radeon/r100.c
+++ b/drivers/gpu/drm/radeon/r100.c
@@ -3809,6 +3809,31 @@ void r100_fini(struct radeon_device *rdev)
         rdev->bios = NULL;
 }
 
+/*
+ * Due to how kexec works, it can leave the hw fully initialised when it
+ * boots the new kernel. However doing our init sequence with the CP and
+ * WB stuff setup causes GPU hangs on the RN50 at least. So at startup
+ * do some quick sanity checks and restore sane values to avoid this
+ * problem.
+ */
+void r100_restore_sanity(struct radeon_device *rdev)
+{
+        u32 tmp;
+
+        tmp = RREG32(RADEON_CP_CSQ_CNTL);
+        if (tmp) {
+                WREG32(RADEON_CP_CSQ_CNTL, 0);
+        }
+        tmp = RREG32(RADEON_CP_RB_CNTL);
+        if (tmp) {
+                WREG32(RADEON_CP_RB_CNTL, 0);
+        }
+        tmp = RREG32(RADEON_SCRATCH_UMSK);
+        if (tmp) {
+                WREG32(RADEON_SCRATCH_UMSK, 0);
+        }
+}
+
 int r100_init(struct radeon_device *rdev)
 {
         int r;
@@ -3821,6 +3846,8 @@ int r100_init(struct radeon_device *rdev)
         radeon_scratch_init(rdev);
         /* Initialize surface registers */
         radeon_surface_init(rdev);
+        /* sanity check some register to avoid hangs like after kexec */
+        r100_restore_sanity(rdev);
         /* TODO: disable VGA need to use VGA request */
         /* BIOS*/
         if (!radeon_get_bios(rdev)) {