drm: radeon: implement RADEON_PARAM_SCRATCH_OFFSET getparam

When this succeeds, userspace can read the scratch register contents from th    mapped writeback page directly.

Signed-off-by: Dave Airlie <airlied@linux.ie>

1 files changed, 5 insertions, 1 deletions

diff --git a/drivers/char/drm/radeon_state.c b/drivers/char/drm/radeon_state.c
index 99589fe0032f..0433ff80cb70 100644
--- a/drivers/char/drm/radeon_state.c
+++ b/drivers/char/drm/radeon_state.c
@@ -2987,7 +2987,11 @@ static int radeon_cp_getparam(DRM_IOCTL_ARGS)
         case RADEON_PARAM_GART_TEX_HANDLE:
                 value = dev_priv->gart_textures_offset;
                 break;
-        
+        case RADEON_PARAM_SCRATCH_OFFSET:
+                if (!dev_priv->writeback_works)
+                        return DRM_ERR(EINVAL);
+                value = RADEON_SCRATCH_REG_OFFSET;
+                break;
         case RADEON_PARAM_CARD_TYPE:
                 if (dev_priv->flags & CHIP_IS_PCIE)
                         value = RADEON_CARD_PCIE;