linux-kernel - Re: [PATCH v2 2/2] iio: adc: imx93_adc: load calibrated values even calibration failed

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Message-ID: <aJto7EJhmkURzJaF@lizhi-Precision-Tower-5810>
Date: Tue, 12 Aug 2025 12:16:44 -0400
From: Frank Li <Frank.li@....com>
To: Haibo Chen <haibo.chen@....com>
Cc: Jonathan Cameron <jic23@...nel.org>,
	David Lechner <dlechner@...libre.com>,
	Nuno Sá <nuno.sa@...log.com>,
	Andy Shevchenko <andy@...nel.org>, Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>, primoz.fiser@...ik.com,
	linux-iio@...r.kernel.org, imx@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] iio: adc: imx93_adc: load calibrated values even
 calibration failed

On Tue, Aug 12, 2025 at 04:04:23PM +0800, Haibo Chen wrote:
> ADC calibration might fail because of the noise on reference voltage.
> To avoid calibration fail, need to meet the following requirement:
>     ADC reference voltage Noise < 1.8V * 1/2^ENOB
>
> For the case which the ADC reference voltage on board do not meet
> the requirement, still load the calibrated values, so ADC can also
> work but maybe not that accurate.
>
> Signed-off-by: Haibo Chen <haibo.chen@....com>

Reviewed-by: Frank Li <Frank.Li@....com>

> ---
>  drivers/iio/adc/imx93_adc.c | 18 +++++++++++++++---
>  1 file changed, 15 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/iio/adc/imx93_adc.c b/drivers/iio/adc/imx93_adc.c
> index 8471737ac04a2bac0417a6397f20865f6a2c01ca..17b0a2548b0a3614ac537b01e28bc3144d17d6fc 100644
> --- a/drivers/iio/adc/imx93_adc.c
> +++ b/drivers/iio/adc/imx93_adc.c
> @@ -38,6 +38,7 @@
>  #define IMX93_ADC_PCDR6		0x118
>  #define IMX93_ADC_PCDR7		0x11C
>  #define IMX93_ADC_CALSTAT	0x39C
> +#define IMX93_ADC_CALCFG0	0x3A0
>
>  /* ADC bit shift */
>  #define IMX93_ADC_MCR_MODE_MASK			BIT(29)
> @@ -58,6 +59,8 @@
>  #define IMX93_ADC_IMR_ECH_MASK			BIT(0)
>  #define IMX93_ADC_PCDR_CDATA_MASK		GENMASK(11, 0)
>
> +#define IMX93_ADC_CALCFG0_LDFAIL_MASK		BIT(4)
> +
>  /* ADC status */
>  #define IMX93_ADC_MSR_ADCSTATUS_IDLE			0
>  #define IMX93_ADC_MSR_ADCSTATUS_POWER_DOWN		1
> @@ -145,7 +148,7 @@ static void imx93_adc_config_ad_clk(struct imx93_adc *adc)
>
>  static int imx93_adc_calibration(struct imx93_adc *adc)
>  {
> -	u32 mcr, msr;
> +	u32 mcr, msr, calcfg;
>  	int ret;
>
>  	/* make sure ADC in power down mode */
> @@ -158,6 +161,11 @@ static int imx93_adc_calibration(struct imx93_adc *adc)
>
>  	imx93_adc_power_up(adc);
>
> +	/* Enable loading of calibrated values even in fail condition */
> +	calcfg = readl(adc->regs + IMX93_ADC_CALCFG0);
> +	calcfg |= IMX93_ADC_CALCFG0_LDFAIL_MASK;
> +	writel(calcfg, adc->regs + IMX93_ADC_CALCFG0);
> +
>  	/*
>  	 * TODO: we use the default TSAMP/NRSMPL/AVGEN in MCR,
>  	 * can add the setting of these bit if need in future.
> @@ -180,9 +188,13 @@ static int imx93_adc_calibration(struct imx93_adc *adc)
>  	/* check whether calbration is success or not */
>  	msr = readl(adc->regs + IMX93_ADC_MSR);
>  	if (msr & IMX93_ADC_MSR_CALFAIL_MASK) {
> +		/*
> +		 * Only give warning here, this means the noise of the
> +		 * reference voltage do not meet the requirement:
> +		 *     ADC reference voltage Noise < 1.8V * 1/2^ENOB
> +		 * And the resault of ADC is not that accurate.
> +		 */
>  		dev_warn(adc->dev, "ADC calibration failed!\n");
> -		imx93_adc_power_down(adc);
> -		return -EAGAIN;
>  	}
>
>  	return 0;
>
> --
> 2.34.1
>