linux-kernel - Re: [PATCH v2 RESEND 2/3] mfd: atmel-hlcdc: fetch LVDS PLL clock for LVDS display

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Message-ID: <20251106130233.GK8064@google.com>
Date: Thu, 6 Nov 2025 13:02:33 +0000
From: Lee Jones <lee@...nel.org>
To: Manikandan Muralidharan <manikandan.m@...rochip.com>
Cc: maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
	tzimmermann@...e.de, airlied@...il.com, simona@...ll.ch,
	nicolas.ferre@...rochip.com, alexandre.belloni@...tlin.com,
	claudiu.beznea@...on.dev, dri-devel@...ts.freedesktop.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	dharma.b@...rochip.com
Subject: Re: [PATCH v2 RESEND 2/3] mfd: atmel-hlcdc: fetch LVDS PLL clock for
 LVDS display

On Wed, 22 Oct 2025, Manikandan Muralidharan wrote:

> 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 first attempts to retrieve sys_clk
> If that fails,it then tries to acquire lvds_pll_clk.
> 
> Signed-off-by: Manikandan Muralidharan <manikandan.m@...rochip.com>
> Signed-off-by: Dharma Balasubiramani <dharma.b@...rochip.com>
> ---
> 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       | 16 ++++++++++++++--
>  include/linux/mfd/atmel-hlcdc.h |  1 +
>  2 files changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mfd/atmel-hlcdc.c b/drivers/mfd/atmel-hlcdc.c
> index 4c4e35d404f3..f680392b01ba 100644
> --- a/drivers/mfd/atmel-hlcdc.c
> +++ b/drivers/mfd/atmel-hlcdc.c
> @@ -108,10 +108,22 @@ static int atmel_hlcdc_probe(struct platform_device *pdev)
>  		return PTR_ERR(hlcdc->periph_clk);
>  	}
>  
> +	/*
> +	 * Retrieve any one of the Main clk required by the LCD to operate:
> +	 *
> +	 * LCDC Generic Clock (sys_clk) - Parallel RGB and MIPI displays,
> +	 * LVDS PLL (lvds_pll_clk)      - LVDS display
> +	 */
>  	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);
> +		dev_warn(dev,
> +			 "failed to get LCDC generic clock, trying for LVDS PLL clock instead\n");

Does the user really care which clock they use?

Can this just happen silently instead?

> +		hlcdc->lvds_pll_clk = devm_clk_get(dev, "lvds_pll_clk");
> +		if (IS_ERR(hlcdc->lvds_pll_clk)) {
> +			dev_err(dev, "failed to get LVDS PLL clock\n");

Failed to obtain both the LCDC (generic) and LVDS PLL clocks

> +			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
> 

-- 
Lee Jones [李琼斯]