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

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Message-ID: <aB2hdA8mfKGlk8d8@pengutronix.de>
Date: Fri, 9 May 2025 08:32:20 +0200
From: Sascha Hauer <s.hauer@...gutronix.de>
To: Nishanth Menon <nm@...com>
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

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.

Sascha

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