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

[Jonathan Cameron <jic23@kernel.org>]

On Tue, 17 Jun 2025 03:07:11 +0000
Bough Chen <haibo.chen@nxp.com> wrote:

> Any comment for this patch?
I guess you didn't receive this mail from Andy for some reason?

https://lore.kernel.org/all/aAkYvE6VtoQItM5o@smile.fi.intel.com/

There were a few minor requested changes in there.
> 
> > -----Original Message-----
> > From: Bough Chen <haibo.chen@nxp.com>
> > Sent: 2025年4月23日 16:03
> > To: Jonathan Cameron <jic23@kernel.org>; David Lechner
> > <dlechner@baylibre.com>; Nuno Sá <nuno.sa@analog.com>; Andy Shevchenko
> > <andy@kernel.org>; Shawn Guo <shawnguo@kernel.org>; Sascha Hauer
> > <s.hauer@pengutronix.de>; Pengutronix Kernel Team
> > <kernel@pengutronix.de>; Fabio Estevam <festevam@gmail.com>
> > Cc: linux-iio@vger.kernel.org; imx@lists.linux.dev;
> > linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org; Bough
> > Chen <haibo.chen@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@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@nxp.com>  
>