linux-kernel - Re: [PATCH] ARM: dts: Fix undocumented LM75 compatible nodes

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Message-ID: <CAL_Jsq+tyKxaDsM2ThXctHhXLXUjCAbDH+90gqDrmMV_-z5PvQ@mail.gmail.com>
Date: Fri, 9 Aug 2024 08:06:37 -0600
From: Rob Herring <robh@...nel.org>
To: Alexander Stein <alexander.stein@...tq-group.com>
Cc: soc@...nel.org, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Joel Stanley <joel@....id.au>, Andrew Jeffery <andrew@...econstruct.com.au>, 
	Dinh Nguyen <dinguyen@...nel.org>, Andrew Lunn <andrew@...n.ch>, 
	Gregory Clement <gregory.clement@...tlin.com>, 
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>, Avi Fishman <avifishman70@...il.com>, 
	Tomer Maimon <tmaimon77@...il.com>, Tali Perry <tali.perry1@...il.com>, 
	Patrick Venture <venture@...gle.com>, Nancy Yuen <yuenn@...gle.com>, 
	Benjamin Fair <benjaminfair@...gle.com>, Shawn Guo <shawnguo@...nel.org>, 
	Sascha Hauer <s.hauer@...gutronix.de>, Pengutronix Kernel Team <kernel@...gutronix.de>, 
	Fabio Estevam <festevam@...il.com>, Vladimir Zapolskiy <vz@...ia.com>, Mark Jackson <mpfj@...flow.co.uk>, 
	Tony Lindgren <tony@...mide.com>, Michal Simek <michal.simek@....com>, 
	linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org, 
	linux-aspeed@...ts.ozlabs.org, linux-kernel@...r.kernel.org, 
	openbmc@...ts.ozlabs.org, imx@...ts.linux.dev, linux-omap@...r.kernel.org
Subject: Re: [PATCH] ARM: dts: Fix undocumented LM75 compatible nodes

On Fri, Aug 9, 2024 at 1:51 AM Alexander Stein
<alexander.stein@...tq-group.com> wrote:
>
> Am Donnerstag, 8. August 2024, 18:49:38 CEST schrieb Rob Herring (Arm):
> > "lm75" without any vendor is undocumented. It works with the Linux
> > kernel since the I2C subsystem will do matches of the compatible string
> > without a vendor prefix to the i2c_device_id and/or driver name.
> >
> > Mostly replace "lm75" with "national,lm75" as that's the original part
> > vendor and the compatible which matches what "lm75" matched with. In a
> > couple of cases the node name or compatible gives a clue to the actual
> > part and vendor and a more specific compatible can be used. In these
> > cases, it does change the variant the kernel picks.
> >
> > "nct75" is an OnSemi part which is compatible with TI TMP75C based on
> > a comparison of the OnSemi NCT75 datasheet and configuration the Linux
> > driver uses. Adding an OnSemi compatible would be an ABI change.
> >
> > "nxp,lm75" is most likely an NXP part. NXP makes a LM75A and LM75B.
> > Both are 11-bit resolution and 100ms sample time, so "national,lm75b" is
> > the closest match.
> >
> > While we're here, fix the node names to use the generic name
> > "temperature-sensor".
> >
> > Signed-off-by: Rob Herring (Arm) <robh@...nel.org>
> > ---
> > SoC maintainers, Please take this directly.
> > ---
> >  .../aspeed/aspeed-bmc-facebook-greatlakes.dts |  2 +-
> >  .../socfpga/socfpga_cyclone5_vining_fpga.dts  |  4 +--
> >  .../dts/marvell/armada-385-clearfog-gtr.dtsi  |  8 ++---
> >  .../boot/dts/nuvoton/nuvoton-npcm730-kudo.dts | 32 +++++++++----------
> >  .../boot/dts/nuvoton/nuvoton-npcm750-evb.dts  |  6 ++--
> >  arch/arm/boot/dts/nxp/imx/imx53-mba53.dts     |  4 +--
> >  arch/arm/boot/dts/nxp/imx/imx53-tqma53.dtsi   |  4 +--
> >  .../dts/nxp/lpc/lpc4357-ea4357-devkit.dts     |  4 +--
> >  .../boot/dts/nxp/lpc/lpc4357-myd-lpc4357.dts  |  2 +-
> >  arch/arm/boot/dts/ti/omap/am335x-nano.dts     |  2 +-
> >  .../boot/dts/xilinx/zynq-zturn-common.dtsi    |  4 +--
> >  11 files changed, 36 insertions(+), 36 deletions(-)
> >
> < [snip]
> > diff --git a/arch/arm/boot/dts/nxp/imx/imx53-mba53.dts b/arch/arm/boot/dts/nxp/imx/imx53-mba53.dts
> > index 2117de872703..d155b3ec22ef 100644
> > --- a/arch/arm/boot/dts/nxp/imx/imx53-mba53.dts
> > +++ b/arch/arm/boot/dts/nxp/imx/imx53-mba53.dts
> > @@ -175,8 +175,8 @@ expander: pca9554@20 {
> >               gpio-controller;
> >       };
> >
> > -     sensor2: lm75@49 {
> > -             compatible = "lm75";
> > +     sensor2: temperature-sensor@49 {
> > +             compatible = "national,lm75";
>
> I checked the old schematics. This is an NXP LM75A, so 'national,lm75a'
> would be the correct compatible.

Thanks for checking. That doesn't change the configuration in the
driver. lm75 and lm75a are treated the same as both are 9-bit
resolution. The NXP LM75A is 11-bit resolution and 10Hz which
corresponds to lm75b in the driver. Though it looks to me like the
original lm75b was also 9-bit resolution.

Rob