linux-kernel - Re: [PATCH v2 1/2] dt-bindings: trivial-devices: add ltp8800

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Message-ID: <20241106-rancidity-unexpired-bd3baf858fef@spud>
Date: Wed, 6 Nov 2024 16:46:10 +0000
From: Conor Dooley <conor@...nel.org>
To: Guenter Roeck <linux@...ck-us.net>
Cc: Cedric Encarnacion <cedricjustine.encarnacion@...log.com>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-i2c@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-hwmon@...r.kernel.org, Jean Delvare <jdelvare@...e.com>,
	Jonathan Corbet <corbet@....net>,
	Delphine CC Chiu <Delphine_CC_Chiu@...ynn.com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Peter Yin <peteryin.openbmc@...il.com>,
	Noah Wang <noahwang.wang@...look.com>, Marek Vasut <marex@...x.de>,
	Lukas Wunner <lukas@...ner.de>
Subject: Re: [PATCH v2 1/2] dt-bindings: trivial-devices: add ltp8800

On Wed, Nov 06, 2024 at 08:35:33AM -0800, Guenter Roeck wrote:
> On 11/6/24 08:06, Conor Dooley wrote:
> > On Tue, Nov 05, 2024 at 08:34:01PM -0800, Guenter Roeck wrote:
> > > On 11/5/24 19:09, Cedric Encarnacion wrote:
> > > > Add Analog Devices LTP8800-1A, LTP8800-2, and LTP8800-4A DC/DC μModule
> > > > regulator.
> > 
> > A single compatible for 3 devices is highly suspect. What is
> > different between these devices?
> > 
> 
> The maximum supported current is different.
> 
> -2:  135A
> -1A: 150A
> -4A: 200A
> 
> Programming is exactly the same, which is why I had asked the submitter to use
> a single compatible property. Sorry for that if it is inappropriate.
> 
> Is there some guidance explaining when to use a single vs. multiple compatible
> properties for different chip variants ?

TBH, I'm biased and a bit paranoid, so I'd probably give them all
compatibles and set one of them as a fallback. If the programming model
is actually identical, then it's probably fair to use a single
compatible (provided the commit message explains exactly why it's safe
to do) unless the different output conditions require using different
regulator output constraints that different compatibles would be
required to enforce.

> Note that there are also LTP8803-1A which supports 160A, and LTP8802A-1B
> which supports 140A. Maybe there are more, but those are the ones I can find in
> public. I don't know if there is a difference from programming perspective compared
> to the LTP8800 chip variants; the datasheets are too vague to be sure. It would be
> useful to know if those chips should get separate compatible entries if programming
> is the same.

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