[PATCH] iio: adc: imx93_adc: load calibrated values even calibration failed

[Bough Chen]

Any comment for this patch?

> -----Original Message-----
> From: Bough Chen <haibo.chen at nxp.com>
> Sent: 2025年4月23日 16:03
> To: Jonathan Cameron <jic23 at kernel.org>; David Lechner
> <dlechner at baylibre.com>; Nuno Sá <nuno.sa at analog.com>; Andy Shevchenko
> <andy at kernel.org>; Shawn Guo <shawnguo at kernel.org>; Sascha Hauer
> <s.hauer at pengutronix.de>; Pengutronix Kernel Team
> <kernel at pengutronix.de>; Fabio Estevam <festevam at gmail.com>
> Cc: linux-iio at vger.kernel.org; imx at lists.linux.dev;
> linux-arm-kernel at lists.infradead.org; linux-kernel at vger.kernel.org; Bough
> Chen <haibo.chen at nxp.com>
> Subject: [PATCH] iio: adc: imx93_adc: load calibrated values even calibration
> failed
> 
> 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 at nxp.com>
> ---
>  drivers/iio/adc/imx93_adc.c | 21 ++++++++++++++++-----
>  1 file changed, 16 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/iio/adc/imx93_adc.c b/drivers/iio/adc/imx93_adc.c index
> 7feaafd2316f246bd0c32fea99309900b5c65099..ebf976db746f02431a315b1faa
> 86f151bb67132e 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.
> @@ -179,11 +187,14 @@ 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) {
> +	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 reault of ADC is not that accurate.
> +		 */
>  		dev_warn(adc->dev, "ADC calibration failed!\n");
> -		imx93_adc_power_down(adc);
> -		return -EAGAIN;
> -	}
> 
>  	return 0;
>  }
> 
> ---
> base-commit: bc8aa6cdadcc00862f2b5720e5de2e17f696a081
> change-id: 20250423-adcpatch-cb59c5255961
> 
> Best regards,
> --
> Haibo Chen <haibo.chen at nxp.com>