linux-kernel - Re: [PATCH v2 14/16] hwmon: (mr75203) parse thermal coefficients from device-tree

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Message-ID: <20220819113842.GD3106213@roeck-us.net>
Date:   Fri, 19 Aug 2022 04:38:42 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     "Farber, Eliav" <farbere@...zon.com>
Cc:     jdelvare@...e.com, robh+dt@...nel.org, mark.rutland@....com,
        linux-hwmon@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, talel@...zon.com, hhhawa@...zon.com,
        jonnyc@...zon.com, hanochu@...zon.com, ronenk@...zon.com,
        itamark@...zon.com, shellykz@...zon.com, shorer@...zon.com,
        amitlavi@...zon.com, almogbs@...zon.com, dwmw@...zon.co.uk,
        rtanwar@...linear.com
Subject: Re: [PATCH v2 14/16] hwmon: (mr75203) parse thermal coefficients
 from device-tree

On Fri, Aug 19, 2022 at 10:57:58AM +0300, Farber, Eliav wrote:
> On 8/18/2022 11:28 PM, Guenter Roeck wrote:
> > The calculation was just changed to use new defaults in a previous
> > patch. This patch makes it quite clear that the coefficients
> > are implementation (?) dependent. So the previous patch just changes
> > the defaults to (presumably) the coefficients used in your system.
> > That is inappropriate. Adding non-default corefficients is ok
> > and makes sense is supported by the chip, but changing defaults
> > isn't.
> The calculation was changed in previous patch to match series 5 of the
> Moortec Embedded Temperature Sensor (METS) datasheet.
> In our SOC we use series 6 which has a slightly different equation and
> different coefficients.

If the coefficients are different based on the series, it would probably
make sense to create a separate devicetree compatible property for series 6
instead or requiring the user to list the actual coefficients. Those can
still be present, but the code should be able to use the defaults for
each series.

Guenter

> I did the changes in steps.
> With this last change, both series 5 and 6 are supported, in addition to
> calibrated vs. non-calibrated modes.
> In addition the data sheet just recommends default values but they also
> specifically mention that actual values might vary from product to product.
> 
> --
> Regards, Eliav