mfd: atmel-hlcdc: Obtain essential clock for LCD operation

Add checks for the presence of the essential clocks necessary for
distinct display interfaces (GCK for PDA and MIPI Display, LVDS PLL
for LVDS Display), as dictated by the Device Tree. The LCD controller
expects one of these clocks to be present but not both, thus obtaining
the required clock to enable LCD functionality.

Fixes: ab9801b ("mfd: atmel-hlcdc: set prepare and enable LVDS PLL clock for LVDS display")
Signed-off-by: Dharma Balasubiramani <dharma.b@microchip.com>

Author: Dharma Balasubiramani

drivers/mfd/atmel-hlcdc.c

@@ -108,17 +108,21 @@ static int atmel_hlcdc_probe(struct platform_device *pdev)
 		return PTR_ERR(hlcdc->periph_clk);
 	}
 
+	/*
+	 * Obtain one of the essential clocks (GCK / LVDS PLL) necessary for
+	 * the LCD to function. GCK for PDA and MIPI Display, LVDS PLL for LVDS
+	 * Display. DT is expected to have any one of the clocks, not both.
+	 */
+	hlcdc->sys_clk = NULL;
+	hlcdc->lvds_pll_clk = NULL;
 	hlcdc->sys_clk = devm_clk_get(dev, "sys_clk");
 	if (IS_ERR(hlcdc->sys_clk)) {
-		dev_err(dev, "failed to get system clock\n");
-		return PTR_ERR(hlcdc->sys_clk);
-	}
-
-	/* Get the optional clock (LVDS PLL) in case if the LVDS interface is used */
-	hlcdc->lvds_pll_clk = devm_clk_get_optional(dev, "lvds_pll_clk");
-	if (IS_ERR(hlcdc->lvds_pll_clk)) {
-		dev_info(dev, "failed to get lvds PLL clock\n");
-		hlcdc->lvds_pll_clk = NULL;
+		dev_dbg(dev, "failed to get sys_clk\n");
+		hlcdc->lvds_pll_clk = devm_clk_get(dev, "lvds_pll_clk");
+		if (IS_ERR(hlcdc->lvds_pll_clk)) {
+			dev_err(dev, "failed to get GCK and LVDS_PLL\n");
+			return PTR_ERR(hlcdc->lvds_pll_clk);
+		}
 	}
 
 	hlcdc->slow_clk = devm_clk_get(dev, "slow_clk");