linux-kernel - Re: [PATCH v2 3/3] serial: core: Allow skipping old serial port initialization

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Message-ID: <CAGXu5j+cOZXCTx3SZT2u5rVv4zDpEhX6hjdp+4DUtN=kE+Q-PQ@mail.gmail.com>
Date:   Wed, 14 Mar 2018 17:55:19 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Daniel Kurtz <djkurtz@...omium.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Aaron Durbin <adurbin@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>, Jiri Slaby <jslaby@...e.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Matthias Brugger <mbrugger@...e.com>,
        David Howells <dhowells@...hat.com>,
        Vignesh R <vigneshr@...com>, Sean Young <sean@...s.org>,
        Jeffy <jeffy.chen@...k-chips.com>,
        Doug Anderson <dianders@...omium.org>,
        Matt Redfearn <matt.redfearn@...s.com>,
        Marc Gonzalez <marc_gonzalez@...madesigns.com>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>
Subject: Re: [PATCH v2 3/3] serial: core: Allow skipping old serial port initialization

On Wed, Mar 14, 2018 at 5:23 PM, Daniel Kurtz <djkurtz@...omium.org> wrote:
> On Wed, Mar 14, 2018 at 5:00 PM Kees Cook <keescook@...omium.org> wrote:
>
>> On Wed, Mar 14, 2018 at 3:58 PM, Kees Cook <keescook@...omium.org> wrote:
>> > On Wed, Mar 14, 2018 at 2:44 PM, Daniel Kurtz <djkurtz@...omium.org>
> wrote:
>> > Sorry for being dense. What tree is this against? I can't find mention
>> > of amdcz in Linus's tree nor linux-next.
>
>> As I watched this email send, I noticed the "3/3" in the Subject. ;) I
>> see the amdcz support now. :P
>> https://patchwork.kernel.org/project/LKML/list/?submitter=18441
>
>> >> diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h
>> >> index a27ef5f56431..02570edaddd8 100644
>> >> --- a/include/linux/serial_8250.h
>> >> +++ b/include/linux/serial_8250.h
>> >> @@ -136,6 +136,12 @@ struct uart_8250_port {
>> >>         struct uart_8250_em485 *em485;
>> >>  };
>> >>
>> >> +#ifdef CONFIG_SERIAL_8250
>> >> +extern bool serial8250_skip_old_ports;
>> >> +#else
>> >> +static const bool serial8250_skip_old_ports;
>> >> +#endif
>> >
>> > Where does serial8250_skip_old_ports get used where CONFIG_SERIAL_8250
>> > isn't defined? (i.e. why is the #ifdef needed here?)
>
>> This question still stands, though.
>
>  From the same patch: https://patchwork.kernel.org/patch/10283641/
>
> if (CONFIG_ACPI_SPCR_TABLE && !CONFIG_SERIAL_8250)
>
> in other words, if serial ports are disabled, but we still want to parse
> the APCI_SPCR_TABLE, which "defaults y if X86".
> Perhaps that logic should be changed (no need to parse ACPI SPCR table if
> we are going to disable serial anyway)?

But won't this break? "static const bool ..." but the code tries to
set a value but I'd expect the compiler to still yet about it?

I think you could drop the .h #ifdef and use:

if (IS_ENABLED(CONFIG_SERIAL_825) && amdcz_present(...)) {

-Kees

-- 
Kees Cook
Pixel Security