linux-kernel - Re: [PATCH v3 2/3] ACPI / OSL: Allow PCI to be disabled

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Message-ID: <CAJZ5v0i+rgLL+KrRs69URbGhUxDK9eUEuLifDWuL2mgpkAv_1g@mail.gmail.com>
Date:   Tue, 11 Dec 2018 23:51:39 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     okaya@...nel.org
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Christoph Hellwig <hch@...radead.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/3] ACPI / OSL: Allow PCI to be disabled

On Tue, Dec 11, 2018 at 11:22 PM Sinan Kaya <okaya@...nel.org> wrote:
>
> On 12/11/2018 5:16 PM, Rafael J. Wysocki wrote:
> >> AFAIK, ACPI spec says that AML code running on non-existing op-regions to be
> >> discarded last time I checked.
> > I guess you mean "disregarded"?
> >
>
> I have seen Linux complain about reads/writes to non-existing I2C opregions
> before as a read/write failure for every single AML transaction. I was under the
> impression that we didn't care.
>
> > So the spec appears to expect the OS to silently ignore the failures
> > in those cases, so why should an error be returned?
> >
>
> I can certainly return success for this case when CONFIG_PCI is not present.
>
> >> I know Linux is noisy about these.

Well, users running kernels with CONFIG_PCI unset on platforms
expecting PCI support to be present in the OS may want to know that I
suppose, so that would be a good reason to return an error, but
perhaps just once rather than on every access (maybe unless debugging
is enabled?).