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

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Message-ID: <20250812165345.000002a4@huawei.com>
Date: Tue, 12 Aug 2025 16:53:45 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Primoz Fiser <primoz.fiser@...ik.com>
CC: Haibo Chen <haibo.chen@....com>, 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>,
	<linux-iio@...r.kernel.org>, <imx@...ts.linux.dev>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
	"upstream@...ts.phytec.de" <upstream@...ts.phytec.de>
Subject: Re: [PATCH v2 2/2] iio: adc: imx93_adc: load calibrated values even
 calibration failed

On Tue, 12 Aug 2025 10:45:48 +0200
Primoz Fiser <primoz.fiser@...ik.com> wrote:

> Hi Haibo,
> 
> On 12. 08. 25 10:04, 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.  
> 
> Reviewed-by: Primoz Fiser <primoz.fiser@...ik.com>
> 
> Thanks for fixing this.
> 
> BR,
> Primoz
> 
> > 
> > Signed-off-by: Haibo Chen <haibo.chen@....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.

result

If nothing else comes up I'll probably just fix that whilst applying.

Jonathan


> > +		 */
> >  		dev_warn(adc->dev, "ADC calibration failed!\n");
> > -		imx93_adc_power_down(adc);
> > -		return -EAGAIN;
> >  	}
> >  
> >  	return 0;
> >   
>