linux-kernel - Re: [PATCH] arm64: dts: ti: k3-am625-sk: Add power/temperature sensors

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Message-ID: <20250509064753.4ntxyozwlebnskod@compound>
Date: Fri, 9 May 2025 01:47:53 -0500
From: Nishanth Menon <nm@...com>
To: Sascha Hauer <s.hauer@...gutronix.de>
CC: Vignesh Raghavendra <vigneshr@...com>, Tero Kristo <kristo@...nel.org>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: dts: ti: k3-am625-sk: Add power/temperature
 sensors

On 08:32-20250509, Sascha Hauer wrote:
> Hi Nishanth,
> 
> On Wed, May 07, 2025 at 07:01:04AM -0500, Nishanth Menon wrote:
> > On 15:24-20250505, Sascha Hauer wrote:
> > > The AM625-SK has six power sensors and two temperature sensors connected
> > > to I2C. Add them to the device tree.
> > > 
> > > Signed-off-by: Sascha Hauer <s.hauer@...gutronix.de>
> > > ---
> > > The AM625-SK has six power sensors and two temperature sensors connected
> > > to I2C. Add them to the device tree.
> > 
> > Sascha,
> > 
> > I suggest making this as overlay. The reason is as follows: AM625-SK
> > among other TI evms do have automated power measurement capability from
> > XDS110 (accessible via USB port for jtag - appears as a rudimentary
> > menu option). The way this works is that it uses TM4C1294NCPDT to use
> > I2C commands to control the INA226/231 depending on the evm.
> > 
> > This firmware should be flashed by default on production boards (if
> > not, starting up CCS[1], autodetects older firmware and updates - at
> > least to my understanding) - by the way, this firmware also does test
> > automation, such as boot mode switch control, reset control etc.
> > 
> > This is the primary framework meant to be used by test automation and
> > indeed it is the default inside TI.
> > 
> > Challenge here is this: if we make this default in Linux, the test
> > automation system configures the INA226/231 in a different sampling
> > mode depending on usecase etc Vs what Linux does (even though the
> > shunt and the bus voltage for a given INA is the same). And just like
> > Linux, the firmware power measurement logic has changed over the
> > years.
> > 
> > Anyways, while I know that the SoC and TM4C can both handle
> > multi-master, the challenge is the same INA controlled and
> > mix-configured by two masters (and there is no synchronization between
> > the two).
> > 
> > To avoid this entire conflict and headache, I suggest adding it as
> > overlay that can be applied depending on the preference of measurement
> > desired.
> 
> Thanks for this explanation. I'll go for the overlay then.

Thanks. do check if the default defconfig needs to be updated as well -
i didn't get a chance to cross verify - will be good to ensure deferred
devices are 0. if something to be enabled, do enable them as modules,
i'd gladly pull it in.

just a headsup - i plan on closing the window today and pick last set of
patches and tag on monday. a bit tight given the window currently..

-- 
Regards,
Nishanth Menon
Key (0xDDB5849D1736249D) / Fingerprint: F8A2 8693 54EB 8232 17A3  1A34 DDB5 849D 1736 249D