linux-kernel - Re: regmap I3C support

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Message-ID: <ZzdjWWrTK1bniwFf@finisterre.sirena.org.uk>
Date: Fri, 15 Nov 2024 15:06:01 +0000
From: Mark Brown <broonie@...nel.org>
To: Guenter Roeck <linux@...ck-us.net>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Frank Li <Frank.Li@....com>
Subject: Re: regmap I3C support

On Thu, Nov 14, 2024 at 10:58:05PM -0800, Guenter Roeck wrote:
> On Thu, Nov 14, 2024 at 05:26:19PM +0000, Mark Brown wrote:

> > Right, so the fact that I3C depends on I2C deals with a lot of the
> > problems that plague the I2C/SPI combination.  Ugh.  I guess the helper
> > should be OK and there's not much doing for I2C/SPI.

> Is it really that difficult for I2C and SPI ? The patch below seems to work
> for the LTC2947 driver. It doesn't even need dummies (the compiler drops
> the unused code), though I am not sure if that can be relied on. I thought
> that dummy functions are needed, but maybe I am wrong.
> 
> The Kconfig for the combined ltc2947 driver is
> 
> config SENSORS_LTC2947
>         tristate "Analog Devices LTC2947 High Precision Power and Energy Monitor"
>         depends on I2C || SPI
>         depends on I2C || I2C=n
>         select REGMAP_I2C if I2C
>         select REGMAP_SPI if SPI

This prevents building the driver in if I2C=m which isn't always
desirable, and IIRC the randconfig people kept turning issues up.  You
can make things work well enough for normal configurations, it's all
edge cases that cause issues.

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