Re: [PATCH 3/3] dt-bindings: pse-pd: ti,tps23881: Add TPS23881B

[Thomas Wismer <thomas@wismer.xyz>]

Am Wed, 8 Oct 2025 14:38:52 +0200
schrieb Andrew Lunn <andrew@lunn.ch>:

> On Wed, Oct 08, 2025 at 01:52:43PM +0200, Thomas Wismer wrote:
> > Am Tue, 7 Oct 2025 21:40:03 +0100
> > schrieb Conor Dooley <conor@kernel.org>:
> >   
> > > On Sat, Oct 04, 2025 at 08:03:53PM +0200, Thomas Wismer wrote:  
> > > > From: Thomas Wismer <thomas.wismer@scs.ch>
> > > > 
> > > > Add the TPS23881B I2C power sourcing equipment controller to the
> > > > list of supported devices.    
> > > 
> > > Missing an explanation for why a fallback compatible is not
> > > suitable here. Seems like it is, if the only difference is that
> > > the firmware is not required to be refreshed, provided that
> > > loading the non-B firmware on a B device would not be
> > > problematic.  
> > 
> > Loading the non-B firmware on a B device is indeed problematic. I'll
> > append the following paragraph to the patch when reposting it after
> > the current merge window has closed.  
> 
> Is it possible to ask the device what it is?

Yes, the devices allow the silicon revision to be read, which would
enable a driver to correctly handle the case distinctions.

> If you can, maybe you don't even need a new compatible, just load the
> appropriate firmware depending on what the device says it is.

When adapting the driver, I also considered an auto-detection mechanism.
However, it felt safer to rely on the devicetree information than reading
a silicon revision register, which has a totally different meaning on
some other device. I have therefore decided to make the driver behaviour
solely dependent on the devicetree information and to use the silicon
revision only as a sanity check (as already implemented in the driver).
Is there any best practice when to use auto-detection with I2C devices?

Regardless of whether the driver queries the silicon revision, the B
device declaration would look somehow strange to me with a driver having
one single compatible, i.e. compatible = "ti,tps23881b", "ti,tps23881".
The first one specifically names the hardware, the fallback is actually
the name of its predecessor, which is strictly speaking not 100%
compatible but required to have the driver loaded.