linux-kernel - Re: regmap I3C support

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Message-ID: <dd02b307-f8e9-4b5d-9a4d-d429c0dff051@roeck-us.net>
Date: Tue, 19 Nov 2024 10:41:05 -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 11/19/24 09:46, Mark Brown wrote:
> On Fri, Nov 15, 2024 at 08:35:04PM -0800, Guenter Roeck wrote:
>> On 11/14/24 09:26, 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.
> 
>> It looks like we can use
> 
>>         if (IS_ENABLED(CONFIG_REGMAP_I3C)) {
>>                 regmap = devm_regmap_init_i3c(i3cdev, &tmp108_regmap_config);
>>                 if (IS_ERR(regmap))
>>                         return dev_err_probe(dev, PTR_ERR(regmap),
>>                                              "Failed to register i3c regmap\n");
>> 		...
>> 	}
> 
>> even if a stub function is not available as long as there is an external
>> declaration.
> 
>> I don't really like it, but it turns out that this kind of code is already used
>> elsewhere in the kernel. It looks like dead code elimination can now assumed
>> to be available when building kernel code. We live and learn.
> 
> Ah, that solves that problem then I guess?


Yes. It actually goes a step further - the IS_ENABLED(CONFIG_REGMAP_I3C)) in the
probe function isn't needed either because the entire i3c probe function is
optimized away if CONFIG_I3C=n.

I'll send a patch dropping the #ifdef in the tmp108 driver after the commit
window closes.

Thanks,
Guenter