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

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Message-ID: <CAJZ5v0hG0o3jxH_HnS76s=VUC28M4fY5yuWxQttGSkCX_SvCSA@mail.gmail.com>
Date: Fri, 11 Oct 2024 13:28:23 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Arnd Bergmann <arnd@...db.de>, 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 1:12 PM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> 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?

Yes, there are at least 2 cases.  May not be relevant, though.

> > 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.

Care to elaborate?