drm/msm/mdp5: Avoid printing error messages for optional clocks

The current behavior is to try to get optional clocks and print a
dev_err message in case of failure. This looks rather confusing
and may increase with the amount of optional clocks.

We may need a cleaner way to handle per-device clocks but in the
meantime, let's reduce the amount of dev_err messages during the
probe.
Signed-off-by: Stephane Viau <sviau@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>

Documentation/devicetree/bindings/drm/msm/mdp.txt

@@ -11,13 +11,14 @@ Required properties:
 - clock-names: the following clocks are required:
   * "core_clk"
   * "iface_clk"
-  * "lut_clk"
   * "src_clk"
   * "hdmi_clk"
   * "mpd_clk"
 
 Optional properties:
 - gpus: phandle for gpu device
+- clock-names: the following clocks are optional:
+  * "lut_clk"
 
 Example:
 

drivers/gpu/drm/msm/mdp/mdp5/mdp5_kms.c

@@ -452,15 +452,19 @@ static void read_hw_revision(struct mdp5_kms *mdp5_kms,
 }
 
 static int get_clk(struct platform_device *pdev, struct clk **clkp,
-		const char *name)
+		const char *name, bool mandatory)
 {
 	struct device *dev = &pdev->dev;
 	struct clk *clk = devm_clk_get(dev, name);
-	if (IS_ERR(clk)) {
+	if (IS_ERR(clk) && mandatory) {
 		dev_err(dev, "failed to get %s (%ld)\n", name, PTR_ERR(clk));
 		return PTR_ERR(clk);
 	}
-	*clkp = clk;
+	if (IS_ERR(clk))
+		DBG("skipping %s", name);
+	else
+		*clkp = clk;
+
 	return 0;
 }
 
@@ -514,25 +518,26 @@ struct msm_kms *mdp5_kms_init(struct drm_device *dev)
 		goto fail;
 	}
 
-	ret = get_clk(pdev, &mdp5_kms->axi_clk, "bus_clk");
+	/* mandatory clocks: */
+	ret = get_clk(pdev, &mdp5_kms->axi_clk, "bus_clk", true);
 	if (ret)
 		goto fail;
-	ret = get_clk(pdev, &mdp5_kms->ahb_clk, "iface_clk");
+	ret = get_clk(pdev, &mdp5_kms->ahb_clk, "iface_clk", true);
 	if (ret)
 		goto fail;
-	ret = get_clk(pdev, &mdp5_kms->src_clk, "core_clk_src");
+	ret = get_clk(pdev, &mdp5_kms->src_clk, "core_clk_src", true);
 	if (ret)
 		goto fail;
-	ret = get_clk(pdev, &mdp5_kms->core_clk, "core_clk");
+	ret = get_clk(pdev, &mdp5_kms->core_clk, "core_clk", true);
 	if (ret)
 		goto fail;
-	ret = get_clk(pdev, &mdp5_kms->lut_clk, "lut_clk");
-	if (ret)
-		DBG("failed to get (optional) lut_clk clock");
-	ret = get_clk(pdev, &mdp5_kms->vsync_clk, "vsync_clk");
+	ret = get_clk(pdev, &mdp5_kms->vsync_clk, "vsync_clk", true);
 	if (ret)
 		goto fail;
 
+	/* optional clocks: */
+	get_clk(pdev, &mdp5_kms->lut_clk, "lut_clk", false);
+
 	/* we need to set a default rate before enabling.  Set a safe
 	 * rate first, then figure out hw revision, and then set a
 	 * more optimal rate: