drm: bridge: samsung-dsim: Fetch pll-clock-frequency automatically

Make the pll-clock-frequency optional.  If it's present, use it
to maintain backwards compatibility with existing hardware.  If it
is absent, read clock rate of "sclk_mipi" to determine the rate.
Since it can be optional, change the message from an error to
dev_info.
Signed-off-by: Adam Ford <aford173@gmail.com>
Tested-by: Chen-Yu Tsai <wenst@chromium.org>
Tested-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Reviewed-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>
Tested-by: Jagan Teki <jagan@amarulasolutions.com> # imx8mm-icore
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230526030559.326566-4-aford173@gmail.com

drivers/gpu/drm/bridge/samsung-dsim.c

@@ -1740,11 +1740,11 @@ static const struct mipi_dsi_host_ops samsung_dsim_ops = {
 };
 
 static int samsung_dsim_of_read_u32(const struct device_node *np,
-				    const char *propname, u32 *out_value)
+				    const char *propname, u32 *out_value, bool optional)
 {
 	int ret = of_property_read_u32(np, propname, out_value);
 
-	if (ret < 0)
+	if (ret < 0 && !optional)
 		pr_err("%pOF: failed to get '%s' property\n", np, propname);
 
 	return ret;
@@ -1757,19 +1757,27 @@ static int samsung_dsim_parse_dt(struct samsung_dsim *dsi)
 	u32 lane_polarities[5] = { 0 };
 	struct device_node *endpoint;
 	int i, nr_lanes, ret;
+	struct clk *pll_clk;
 
 	ret = samsung_dsim_of_read_u32(node, "samsung,pll-clock-frequency",
-				       &dsi->pll_clk_rate);
-	if (ret < 0)
-		return ret;
+				       &dsi->pll_clk_rate, 1);
+	/* If it doesn't exist, read it from the clock instead of failing */
+	if (ret < 0) {
+		dev_dbg(dev, "Using sclk_mipi for pll clock frequency\n");
+		pll_clk = devm_clk_get(dev, "sclk_mipi");
+		if (!IS_ERR(pll_clk))
+			dsi->pll_clk_rate = clk_get_rate(pll_clk);
+		else
+			return PTR_ERR(pll_clk);
+	}
 
 	ret = samsung_dsim_of_read_u32(node, "samsung,burst-clock-frequency",
-				       &dsi->burst_clk_rate);
+				       &dsi->burst_clk_rate, 0);
 	if (ret < 0)
 		return ret;
 
 	ret = samsung_dsim_of_read_u32(node, "samsung,esc-clock-frequency",
-				       &dsi->esc_clk_rate);
+				       &dsi->esc_clk_rate, 0);
 	if (ret < 0)
 		return ret;