linux-kernel - RE: [PATCH 1/2] dt-bindings: iio: adc: imx93: Add calibration properties

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Message-ID:
 <DU0PR04MB9496AED41C069FB2456954A6902CA@DU0PR04MB9496.eurprd04.prod.outlook.com>
Date: Thu, 7 Aug 2025 09:26:11 +0000
From: Bough Chen <haibo.chen@....com>
To: Primoz Fiser <primoz.fiser@...ik.com>, "Peng Fan (OSS)"
	<peng.fan@....nxp.com>, Nuno S? <noname.nuno@...il.com>
CC: Jonathan Cameron <jic23@...nel.org>, David Lechner
	<dlechner@...libre.com>, Nuno Sa <nuno.sa@...log.com>, Andy Shevchenko
	<andy@...nel.org>, Rob Herring <robh@...nel.org>, Krzysztof Kozlowski
	<krzk+dt@...nel.org>, Conor Dooley <conor+dt@...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" <linux-iio@...r.kernel.org>,
	"imx@...ts.linux.dev" <imx@...ts.linux.dev>, "devicetree@...r.kernel.org"
	<devicetree@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "upstream@...ts.phytec.de"
	<upstream@...ts.phytec.de>, "andrej.picej@...ik.com" <andrej.picej@...ik.com>
Subject: RE: [PATCH 1/2] dt-bindings: iio: adc: imx93: Add calibration
 properties

> -----Original Message-----
> From: Primoz Fiser <primoz.fiser@...ik.com>
> Sent: 2025年8月7日 12:37
> To: Bough Chen <haibo.chen@....com>; Peng Fan (OSS)
> <peng.fan@....nxp.com>; Nuno S? <noname.nuno@...il.com>
> Cc: Jonathan Cameron <jic23@...nel.org>; David Lechner
> <dlechner@...libre.com>; Nuno Sa <nuno.sa@...log.com>; Andy Shevchenko
> <andy@...nel.org>; Rob Herring <robh@...nel.org>; Krzysztof Kozlowski
> <krzk+dt@...nel.org>; Conor Dooley <conor+dt@...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;
> devicetree@...r.kernel.org; linux-arm-kernel@...ts.infradead.org;
> linux-kernel@...r.kernel.org; upstream@...ts.phytec.de;
> andrej.picej@...ik.com
> Subject: Re: [PATCH 1/2] dt-bindings: iio: adc: imx93: Add calibration properties
> 
> Hi,
> 
> On 21. 07. 25 11:09, Bough Chen wrote:
> >> -----Original Message-----
> >> From: Peng Fan (OSS) <peng.fan@....nxp.com>
> >> Sent: 2025年7月21日 17:39
> >> To: Nuno S? <noname.nuno@...il.com>
> >> Cc: Primoz Fiser <primoz.fiser@...ik.com>; Jonathan Cameron
> >> <jic23@...nel.org>; David Lechner <dlechner@...libre.com>; Bough Chen
> >> <haibo.chen@....com>; Nuno Sa <nuno.sa@...log.com>; Andy
> Shevchenko
> >> <andy@...nel.org>; Rob Herring <robh@...nel.org>; Krzysztof Kozlowski
> >> <krzk+dt@...nel.org>; Conor Dooley <conor+dt@...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;
> >> devicetree@...r.kernel.org; linux-arm-kernel@...ts.infradead.org;
> >> linux-kernel@...r.kernel.org; upstream@...ts.phytec.de;
> >> andrej.picej@...ik.com
> >> Subject: Re: [PATCH 1/2] dt-bindings: iio: adc: imx93: Add
> >> calibration properties
> >>
> >> On Mon, Jul 14, 2025 at 05:11:31PM +0100, Nuno S? wrote:
> >>> On Mon, 2025-07-14 at 07:56 +0200, Primoz Fiser wrote:
> >>>> Hi all,
> >>>>
> >>>> On 13. 07. 25 17:02, Jonathan Cameron wrote:
> >>>>> On Thu, 10 Jul 2025 10:46:44 -0500 David Lechner
> >>>>> <dlechner@...libre.com> wrote:
> >>>>>
> >>>>>> On 7/10/25 2:39 AM, Primoz Fiser wrote:
> >>>>>>> From: Andrej Picej <andrej.picej@...ik.com>
> >>>>>>>
> >>>>>>> Document i.MX93 ADC calibration properties and how to set them.
> >>>>>>>
> >>>>>>> Signed-off-by: Andrej Picej <andrej.picej@...ik.com>
> >>>>>>> Signed-off-by: Primoz Fiser <primoz.fiser@...ik.com>
> >>>>>>> ---
> >>>>>>> ??.../bindings/iio/adc/nxp,imx93-adc.yaml???????????? | 21
> >>>>>>> +++++++++++++++++++
> >>>>>>> ??1 file changed, 21 insertions(+)
> >>>>>>>
> >>>>>>> diff --git
> >>>>>>> a/Documentation/devicetree/bindings/iio/adc/nxp,imx93-
> >>>>>>> adc.yaml
> >>>>>>> b/Documentation/devicetree/bindings/iio/adc/nxp,imx93-adc.yaml
> >>>>>>> index c2e5ff418920..d1c04cf85fe6 100644
> >>>>>>> ---
> >>>>>>> a/Documentation/devicetree/bindings/iio/adc/nxp,imx93-adc.yaml
> >>>>>>> +++ b/Documentation/devicetree/bindings/iio/adc/nxp,imx93-adc.y
> >>>>>>> +++ aml
> >>>>>>> @@ -52,6 +52,27 @@ properties:
> >>>>>>> ???? "#io-channel-cells":
> >>>>>>> ???????? const: 1
> >>>>>>> ??
> >>>>>>> +?? nxp,calib-avg-en:
> >>>>>>> +?????? default: 1
> >>>>>>> +?????? description:
> >>>>>>> +?????????? Enable or disable calibration averaging function (AVGEN).
> >>>>>>> +?????? $ref: /schemas/types.yaml#/definitions/uint32
> >>>>>>> +?????? enum: [ 0, 1 ]
> >>>>>>> +
> >>>>>>> +?? nxp,calib-nr-samples:
> >>>>>>> +?????? default: 512
> >>>>>>> +?????? description:
> >>>>>>> +?????????? Selects number of samples (NRSMPL) to be used during
> >> calibration.
> >>>>>>> +?????? $ref: /schemas/types.yaml#/definitions/uint32
> >>>>>>> +?????? enum: [ 16, 32, 128, 512 ]
> >>>>>
> >>>>> Allow 1 as a value and drop the enabled above.???? Averaging over
> >>>>> 1 sample is same as no averaging and gives simpler binding.
> >>>>>
> >>>>>>> +
> >>>>>>> +?? nxp,calib-t-sample:
> >>>>>>> +?????? default: 22
> >>>>>>> +?????? description:
> >>>>>>> +?????????? Selects sample time (TSAMP) of calibration
> >>>>>>> +conversions in ADC
> >>>>>>> clock cycles
> >>>>>>> +?????? $ref: /schemas/types.yaml#/definitions/uint32
> >>>>>>> +?????? enum: [ 8, 16, 22, 32 ]
> >>>>>>> +
> >>>>>>> ??required:
> >>>>>>> ???? - compatible
> >>>>>>> ???? - reg??
> >>>>>>
> >>>>>> This seem like things that should be set at runtime rather than
> >>>>>> in the devicetree. Unless there is some justification on why
> >>>>>> these values depend on how the chip is wired up?
> >>>>
> >>>> It depends how ADC 1.8V Vref is wired up, especially how noisy it is.
> >>>>
> >>>>>
> >>>>> Further to that, I'd like to see some explanation of why we care
> >>>>> to change it at all. Is it ever a bad idea to enable averaging and
> >>>>> pick a large number of samples for calibration?
> >>>>
> >>>> This is a snippet from the i.MX93 TRM, chapter Analog-to-Digital
> >>>> Converter (SAR_ADC) describing calibration steps:
> >>>>
> >>>> 1. Wait for deassertion of functional reset.
> >>>> 2. Configure SAR controller operating clock (MCR[ADCLKSE] = 0).
> >>>> 3. Bring ADC out of Power-down state (MCR[PWDN] = 0).
> >>>> 4. Configure desired calibration settings (default values kept for
> >>>> highest accuracy maximum time).
> >>>> ??? MCR[TSAMP]: Sample time for calibration conversion ???
> >>>> MCR[NRSMPL]: Number of samples in averaging ??? MCR[AVGEN]:
> >>>> Averaging function enable in calibration 5. Run calibration by
> >>>> writing a one to MCR[CALSTART].
> >>>> 6. Check calibration run status in MSR[CALBUSY]???wait until
> >>>> MSR[CALBUSY] = 0; alternatively, MSR[ADCSTAT] can be used to check
> >>>> status.
> >>>> 7. Check calibration pass/fail status in MSR[CALFAIL] field. If
> >>>> MSR[CALFAIL] = 1 then calibration failed. Detailed status can be
> >>>> checked in CALSTAT.
> >>>>
> >>>>
> >>>> See point 4).
> >>>>
> >>>> Not sure why would there be an option to configure i.MX93 ADC
> >>>> calibration parameters if one use-case (max accuracy max time) to
> >>>> rule them all?
> >>>>
> >>>
> >>> Sometimes HW guys just want to give you some options. Does not mean
> >>> we have to use them all :).
> >>>
> >>> I guess what Jonathan is interested in, is to understand in what
> >>> conditions the defaults are no good for the calibration? If we can
> >>> have a set of values that should pretty much always work, no need to
> >>> further complicate the bindings or the driver.
> >>
> >> Just my understanding, it is hard to use one fixed settings to fit
> >> all kinds of conditions.
> >>
> >>                  Noise induced from PCB tracks  Electro- magnetic
> noise
> >> 		     |                           |
> >> 		     V                           V
> >>  ---------
> >> |SOC(ADC)|   <---------------------------------<- (~) external Signal
> >>  ---------
> >>                  ^                 ^
> >>                  |                 |
> >>              I/O coupled noise    Internal noise
> >>
> >>
> >> So OEM A's board may needs different settings compared with OEM B's
> board.
> >
> > The noise on Vref did impact the calibration, we did get report from customer,
> and IC guys suggested to do like the following patch, what's your comments?
> >
> > https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpatc
> > hwork.kernel.org%2Fproject%2Flinux-iio%2Fpatch%2F20250423-adcpatch-v1-
> >
> 1-b0e84c27ae98%40nxp.com%2F&data=05%7C02%7Chaibo.chen%40nxp.com
> %7C2101
> >
> ebdd274b4dc119fa08ddd56c1e7f%7C686ea1d3bc2b4c6fa92cd99c5c301635%7
> C0%7C
> >
> 0%7C638901382543508027%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcG
> kiOnRydWU
> >
> sIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D
> %
> >
> 7C0%7C%7C%7C&sdata=gW%2F7FPCrcyVSduyj0dK%2BVm4rQJ4hviEsTlTJ06uvH
> 0M%3D&
> > reserved=0
> 
> With this patch we still get calibration warning however ADC is eventually
> working.
> 
> Where can we get mapping for this register:
> 
> #define IMX93_ADC_CALCFG0	0X3A0
> 
> It seems that public i.MX 93 TRM goes up to offset 0x39C only?

You can get the RM our nxp.com, the latest RM already add register 3A0 definition, here is the link,:
https://www.nxp.com/products/processors-and-microcontrollers/arm-processors/i-mx-applications-processors/i-mx-9-processors/i-mx-93-applications-processor-family-arm-cortex-a55-ml-acceleration-power-efficient-mpu:i.MX93

I will send out v2 of this patch.

Regards
Haibo Chen
> 
> BR,
> Primoz
> 
> >
> > Regards
> > Haibo Chen
> >>
> >> Regards,
> >> Peng
> >>
> >>>
> >>> - Nuno S??
> >>>> On the other hand, public TRM doesn't give much more information
> >>>> and
> >>>>>
> 
> --
> Primoz Fiser
> phone: +386-41-390-545
> email: primoz.fiser@...ik.com
> --
> Norik systems d.o.o.
> Your embedded software partner
> Slovenia, EU
> phone: +386-41-540-545
> email: info@...ik.com