drm/etnaviv: add support for slave interface clock

The slave interface clock is a clock input found on newer cores to gate
the register interface. For now we simply ungate it when the GPU is in
active state.
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>

drivers/gpu/drm/etnaviv/etnaviv_gpu.c

@@ -1383,6 +1383,12 @@ static int etnaviv_gpu_clk_enable(struct etnaviv_gpu *gpu)
 {
 	int ret;
 
+	if (gpu->clk_reg) {
+		ret = clk_prepare_enable(gpu->clk_reg);
+		if (ret)
+			return ret;
+	}
+
 	if (gpu->clk_bus) {
 		ret = clk_prepare_enable(gpu->clk_bus);
 		if (ret)
@@ -1421,6 +1427,8 @@ static int etnaviv_gpu_clk_disable(struct etnaviv_gpu *gpu)
 		clk_disable_unprepare(gpu->clk_core);
 	if (gpu->clk_bus)
 		clk_disable_unprepare(gpu->clk_bus);
+	if (gpu->clk_reg)
+		clk_disable_unprepare(gpu->clk_reg);
 
 	return 0;
 }
@@ -1676,6 +1684,11 @@ static int etnaviv_gpu_platform_probe(struct platform_device *pdev)
 	}
 
 	/* Get Clocks: */
+	gpu->clk_reg = devm_clk_get(&pdev->dev, "reg");
+	DBG("clk_reg: %p", gpu->clk_reg);
+	if (IS_ERR(gpu->clk_reg))
+		gpu->clk_reg = NULL;
+
 	gpu->clk_bus = devm_clk_get(&pdev->dev, "bus");
 	DBG("clk_bus: %p", gpu->clk_bus);
 	if (IS_ERR(gpu->clk_bus))

drivers/gpu/drm/etnaviv/etnaviv_gpu.h

@@ -147,6 +147,7 @@ struct etnaviv_gpu {
 
 	/* Power Control: */
 	struct clk *clk_bus;
+	struct clk *clk_reg;
 	struct clk *clk_core;
 	struct clk *clk_shader;