drm/radeon: Enable sdma preemption

This patch adds to radeon the enablement of sdma preemption.
This is needed to support HWS of SDMA user-mode queues.
Signed-off-by: Ben Goz <ben.goz@amd.com>
Signed-off-by: Oded Gabbay <oded.gabbay@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/cik_sdma.c

@@ -282,6 +282,33 @@ static void cik_sdma_rlc_stop(struct radeon_device *rdev)
 	/* XXX todo */
 }
 
+/**
+ * cik_sdma_ctx_switch_enable - enable/disable sdma engine preemption
+ *
+ * @rdev: radeon_device pointer
+ * @enable: enable/disable preemption.
+ *
+ * Halt or unhalt the async dma engines (CIK).
+ */
+void cik_sdma_ctx_switch_enable(struct radeon_device *rdev, bool enable)
+{
+	uint32_t reg_offset, value;
+	int i;
+
+	for (i = 0; i < 2; i++) {
+		if (i == 0)
+			reg_offset = SDMA0_REGISTER_OFFSET;
+		else
+			reg_offset = SDMA1_REGISTER_OFFSET;
+		value = RREG32(SDMA0_CNTL + reg_offset);
+		if (enable)
+			value |= AUTO_CTXSW_ENABLE;
+		else
+			value &= ~AUTO_CTXSW_ENABLE;
+		WREG32(SDMA0_CNTL + reg_offset, value);
+	}
+}
+
 /**
  * cik_sdma_enable - stop the async dma engines
  *
@@ -312,6 +339,8 @@ void cik_sdma_enable(struct radeon_device *rdev, bool enable)
 			me_cntl |= SDMA_HALT;
 		WREG32(SDMA0_ME_CNTL + reg_offset, me_cntl);
 	}
+
+	cik_sdma_ctx_switch_enable(rdev, enable);
 }
 
 /**