linux-kernel - Re: [PATCH v2 2/3] acpi: allow building without CONFIG_HAS

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Message-ID: <ZwkIFREb1Ia90hSR@smile.fi.intel.com>
Date: Fri, 11 Oct 2024 14:12:21 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Arnd Bergmann <arnd@...db.de>
Cc: Arnd Bergmann <arnd@...nel.org>,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	Len Brown <lenb@...nel.org>,
	Mario Limonciello <mario.limonciello@....com>,
	Jarred White <jarredwhite@...ux.microsoft.com>,
	Perry Yuan <perry.yuan@....com>,
	Easwar Hariharan <eahariha@...ux.microsoft.com>,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] acpi: allow building without CONFIG_HAS_IOPORT

On Fri, Oct 11, 2024 at 09:59:46AM +0000, Arnd Bergmann wrote:
> On Fri, Oct 11, 2024, at 09:53, Andy Shevchenko wrote:
> > On Fri, Oct 11, 2024 at 06:18:18AM +0000, Arnd Bergmann wrote:

...

> >> +	if (!IS_ENABLED(CONFIG_HAS_IOPORT)) {
> >> +		*value = BIT_MASK(width);
> >> +		return AE_NOT_IMPLEMENTED;
> >
> > Perhaps it has already been discussed, but why do we need to file value with
> > semi-garbage when we know it's invalid anyway?
> 
> It's not strictly necessary, just precaution for possible callers
> that use the resulting data without checking the error code.

Do you have any examples of that in the kernel?

> The all-ones data is what an x86 PC would see when an I/O
> port is read that is not connected to any device.

Yes, but it's not what your code does.

-- 
With Best Regards,
Andy Shevchenko