drm/rockchip: analogix_dp: introduce the pclk for grf

For RK3399's GRF module, if we want to operate the graphic related grf
registers, we need to enable the pclk_vio_grf which supply power for VIO
GRF IOs, so it's better to introduce an optional grf clock in driver.

Signed-off-by: Yakir Yang <[e-mail]>
Reviewed-by: Douglas Anderson <[e-mail]>
Reviewed-by: Tomasz Figa <[e-mail]>

Documentation/devicetree/bindings/display/rockchip/analogix_dp-rockchip.txt

···
     Port 0: contained 2 endpoints, connecting to the output of vop.
     Port 1: contained 1 endpoint, connecting to the input of panel.
 
+Optional property for different chips:
+- clocks: from common clock binding: handle to grf_vio clock.
+
+- clock-names: from common clock binding:
+	       Required elements: "grf"
+
 For the below properties, please refer to Analogix DP binding document:
  * Documentation/devicetree/bindings/drm/bridge/analogix_dp.txt
 - phys (required)

drivers/gpu/drm/rockchip/analogix_dp-rockchip.c

···
 	struct drm_display_mode  mode;
 
 	struct clk               *pclk;
+	struct clk               *grfclk;
 	struct regmap            *grf;
 	struct reset_control     *rst;
 
···
 
 	dev_dbg(dp->dev, "vop %s output to dp\n", (ret) ? "LIT" : "BIG");
 
-	ret = regmap_write(dp->grf, dp->data->lcdsel_grf_reg, val);
-	if (ret != 0) {
-		dev_err(dp->dev, "Could not write to GRF: %d\n", ret);
+	ret = clk_prepare_enable(dp->grfclk);
+	if (ret < 0) {
+		dev_err(dp->dev, "failed to enable grfclk %d\n", ret);
 		return;
 	}
+
+	ret = regmap_write(dp->grf, dp->data->lcdsel_grf_reg, val);
+	if (ret != 0)
+		dev_err(dp->dev, "Could not write to GRF: %d\n", ret);
+
+	clk_disable_unprepare(dp->grfclk);
 }
 
 static void rockchip_dp_drm_encoder_nop(struct drm_encoder *encoder)
···
 	if (IS_ERR(dp->grf)) {
 		dev_err(dev, "failed to get rockchip,grf property\n");
 		return PTR_ERR(dp->grf);
+	}
+
+	dp->grfclk = devm_clk_get(dev, "grf");
+	if (PTR_ERR(dp->grfclk) == -ENOENT) {
+		dp->grfclk = NULL;
+	} else if (PTR_ERR(dp->grfclk) == -EPROBE_DEFER) {
+		return -EPROBE_DEFER;
+	} else if (IS_ERR(dp->grfclk)) {
+		dev_err(dev, "failed to get grf clock\n");
+		return PTR_ERR(dp->grfclk);
 	}
 
 	dp->pclk = devm_clk_get(dev, "pclk");