[PATCH v3 1/4] mfd: atmel-hlcdc: fetch LVDS PLL clock for LVDS display

[Manikandan Muralidharan <manikandan.m@microchip.com>]

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>
---
changes in v3:
- Rephrase the comments, err logs.
- assign NULL to sys_clk to avoid Oops error when
referenced in pwm-atmel-hlcdc.c

changes in v2:
- Rephrase the comments, commit message and err logs
- Replace dev_err wwith dev_warn
- Remove Initializing sys_clk and lvds_pll_clk to NULL post
devm_kzalloc() call
---
 drivers/mfd/atmel-hlcdc.c       | 13 +++++++++++--
 include/linux/mfd/atmel-hlcdc.h |  1 +
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/mfd/atmel-hlcdc.c b/drivers/mfd/atmel-hlcdc.c
index 4c4e35d404f3..0f83ad7ba15c 100644
--- a/drivers/mfd/atmel-hlcdc.c
+++ b/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");
diff --git a/include/linux/mfd/atmel-hlcdc.h b/include/linux/mfd/atmel-hlcdc.h
index 80d675a03b39..07c2081867fd 100644
--- a/include/linux/mfd/atmel-hlcdc.h
+++ b/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;
-- 
2.25.1