linux-kernel - Re: regmap I3C support

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Message-ID: <Zz0PkWwR28NSlz7L@lizhi-Precision-Tower-5810>
Date: Tue, 19 Nov 2024 17:22:09 -0500
From: Frank Li <Frank.li@....com>
To: Guenter Roeck <linux@...ck-us.net>
Cc: Mark Brown <broonie@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: regmap I3C support

On Tue, Nov 19, 2024 at 01:57:38PM -0800, Guenter Roeck wrote:
> On 11/19/24 11:30, Frank Li wrote:
> > On Tue, Nov 19, 2024 at 10:41:05AM -0800, Guenter Roeck wrote:
> > > 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.
> >
> > Already tried this at v3
> > https://lore.kernel.org/imx/7bdd2db8-41c8-43d8-ae73-84a221d2d004@roeck-us.net/
> >
>
> Yes, I know. Sorry for that. We live and learn. I didn't think this works,
> but it does.
>
> > but I am not sure if it is good on rely on the compiler. Maybe some option
> > like some debug option or -O0 cause problem.
> >
>
> Yes, I thought so too, but it turns out that the kernel doesn't build anymore
> with -O0 anyway, and other code already _does_ depend on dead code elimination.

Good to know this, which keep life simple.

Frank

>
> Guenter
>