linux-kernel - Re: regmap I3C support

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Message-ID: <6344faca-d312-48c1-91a3-7b2b80f4a529@roeck-us.net>
Date: Fri, 15 Nov 2024 07:46:23 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Mark Brown <broonie@...nel.org>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 Frank Li <Frank.Li@....com>
Subject: Re: regmap I3C support

On 11/15/24 07:06, Mark Brown wrote:
> 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.

You mean if SPI=y and I2C=m ? Good point. That isn't normally a problem
for sensor drivers, but I understand that it may be undesirable for others.

Thanks,
Guenter