mfd: atmel-hlcdc: Fetch LVDS PLL clock for LVDS display

The XLCDC IP supports parallel RGB, MIPI DSI and LVDS Display.
The LCD Generic clock (sys_clk) is used for Parallel RGB and MIPI
displays, while the LVDS PLL clock (lvds_pll_clk) is used for LVDS
displays.Since both the clocks cannot co-exist together in the DT
for a given display, this patch tries sys_clk first (RGB/MIPI),
fallback to lvds_pll_clk (LVDS).

Signed-off-by: Manikandan Muralidharan <manikandan.m@microchip.com>
Signed-off-by: Dharma Balasubiramani <dharma.b@microchip.com>
Link: https://patch.msgid.link/20260223101920.284697-2-manikandan.m@microchip.com
Signed-off-by: Lee Jones <lee@kernel.org>

Author: manikandan-m11

drivers/mfd/atmel-hlcdc.c

@@ -108,10 +108,19 @@ static int atmel_hlcdc_probe(struct platform_device *pdev)
 		return PTR_ERR(hlcdc->periph_clk);
 	}
 
+	/*
+	 * Retrieve one of the primary clocks required for LCD operation:
+	 * prefer sys_clk (for RGB/MIPI), and fall back to lvds_pll_clk
+	 * (for LVDS) if needed.
+	 */
 	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);
+		hlcdc->sys_clk = NULL;
+		hlcdc->lvds_pll_clk = devm_clk_get(dev, "lvds_pll_clk");
+		if (IS_ERR(hlcdc->lvds_pll_clk)) {
+			dev_err(dev, "Failed to obtain both the LCDC (generic) and LVDS PLL clocks\n");
+			return PTR_ERR(hlcdc->lvds_pll_clk);
+		}
 	}
 
 	hlcdc->slow_clk = devm_clk_get(dev, "slow_clk");

include/linux/mfd/atmel-hlcdc.h

@@ -75,6 +75,7 @@
  */
 struct atmel_hlcdc {
 	struct regmap *regmap;
+	struct clk *lvds_pll_clk;
 	struct clk *periph_clk;
 	struct clk *sys_clk;
 	struct clk *slow_clk;