linux-kernel - Re: [PATCH v4 1/4] hwmon: lm75: Add lm75 to of

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Date:   Wed, 10 Feb 2021 13:47:34 -0600
From:   Rob Herring <robh@...nel.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     "Matwey V. Kornilov" <matwey@....msu.ru>,
        Jean Delvare <jdelvare@...e.com>,
        "open list:HARDWARE MONITORING" <linux-hwmon@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 1/4] hwmon: lm75: Add lm75 to of_match list

On Sat, Feb 06, 2021 at 08:46:16AM -0800, Guenter Roeck wrote:
> On 2/6/21 1:51 AM, Matwey V. Kornilov wrote:
> > Currently, many boards use just 'lm75' as a compatible string.
> > 
> > Signed-off-by: Matwey V. Kornilov <matwey@....msu.ru>
> > ---
> >  Documentation/devicetree/bindings/hwmon/lm75.yaml | 1 +
> >  drivers/hwmon/lm75.c                              | 4 ++++
> >  2 files changed, 5 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/hwmon/lm75.yaml b/Documentation/devicetree/bindings/hwmon/lm75.yaml
> > index 96eed5cc7841..aec8edd1e0c6 100644
> > --- a/Documentation/devicetree/bindings/hwmon/lm75.yaml
> > +++ b/Documentation/devicetree/bindings/hwmon/lm75.yaml
> > @@ -13,6 +13,7 @@ maintainers:
> >  properties:
> >    compatible:
> >      enum:
> > +      - lm75
> 
> Please split the .yaml file changes into a single patch, separate
> from the code changes. Also please make sure that the subject indicates
> that this is a bindings change.
> 
> For this change, we'll definitely need feedback from Rob. I am not sure
> if such a generic compatible string is permitted or if we need to change
> the dts files instead.
> 
> On a higher level, while lm75 is an extreme case, I see a few other
> violators as well.
> 
> drivers/macintosh/windfarm_ad7417_sensor.c:     { .compatible = "ad7417", },
> drivers/macintosh/windfarm_max6690_sensor.c:    { .compatible = "max6690", },

Old as dirt PowerMac stuff...

> arch/arm/boot/dts/socfpga_arria10_socdk.dtsi:           compatible = "ltc2977";
> arch/arm/boot/dts/aspeed-bmc-arm-centriq2400-rep.dts:                           compatible = "tmp421";

Pretty much a dead platform...

> arch/arm/boot/dts/nuvoton-npcm750-evb.dts:              compatible = "tmp100";
> arch/arm/boot/dts/nuvoton-npcm750-evb.dts:              compatible = "tmp100";
> 
> so it would be good to know how to handle those in general.

The dts files can be fixed without a compatibility issue (at least for 
Linux), so we should update them and leave the documentation as-is. We 
just can't add a new vendor compatible to the driver and then change the 
dts files like these as old kernels wouldn't recognized the new 
compatibles (though we should backport compatibles like PCI IDs).

> 
> Note that there is also:
> 
> Documentation/devicetree/bindings/display/repaper.txt:          compatible = "lm75b";
> 
> but maybe that doesn't matter as much since it is not actually
> used in dts files.

Right.

Rob