linux-kernel - Re: [PATCH] init: Don't proxy console= to earlycon

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Date:   Fri, 14 Jul 2023 18:38:21 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Raul Rangel <rrangel@...omium.org>
Cc:     Randy Dunlap <rdunlap@...radead.org>,
        Mario Limonciello <mario.limonciello@....com>,
        linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        kramasub@...omium.org, Alexander Potapenko <glider@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Li Zhe <lizhe.67@...edance.com>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Mark Rutland <mark.rutland@....com>,
        Will Deacon <will@...nel.org>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Zhou jie <zhoujie@...china.com>
Subject: Re: [PATCH] init: Don't proxy console= to earlycon

On Mon 2023-07-10 09:30:19, Raul Rangel wrote:
> On Sun, Jul 9, 2023 at 8:43 PM Randy Dunlap <rdunlap@...radead.org> wrote:
> >
> >
> >
> > On 7/9/23 18:15, Mario Limonciello wrote:
> > > On 7/9/23 18:46, Randy Dunlap wrote:
> > >>
> > >>
> > >> On 7/7/23 18:17, Raul E Rangel wrote:
> > >>> Right now we are proxying the `console=XXX` command line args to the
> > >>> param_setup_earlycon. This is done because the following are
> > >>> equivalent:
> > >>>
> > >>>      console=uart[8250],mmio,<addr>[,options]
> > >>>      earlycon=uart[8250],mmio,<addr>[,options]
> > >>>
> > >>> In addition, when `earlycon=` or just `earlycon` is specified on the
> > >>> command line, we look at the SPCR table or the DT to extract the device
> > >>> options.
> > >>>
> > >>> When `console=` is specified on the command line, it's intention is to
> > >>> disable the console. Right now since we are proxying the `console=`
> > >>
> > >> How do you figure this (its intention is to disable the console)?
> > >
> 
> https://www.kernel.org/doc/html/v6.1/admin-guide/kernel-parameters.html
> says the following:
> console=
>     { null | "" }
>             Use to disable console output, i.e., to have kernel
>             console messages discarded.
>             This must be the only console= parameter used on the
>             kernel command line.
> 
>         earlycon=       [KNL] Output early console device and options.
> 
>             When used with no options, the early console is
>             determined by stdout-path property in device tree's
>             chosen node or the ACPI SPCR table if supported by
>             the platform.

Sigh, I wasn't aware of this when we discussed the console= handling.

> The reason this bug showed up is that ChromeOS has set `console=` for a
> very long time:
> https://chromium.googlesource.com/chromiumos/platform/crosutils/+/main/build_kernel_image.sh#282
> I'm not sure on the exact history, but AFAIK, we don't have the ttyX devices.
>
> Coreboot recently added support for the ACPI SPCR table which in
> combination with the
> `console=` arg, we are now seeing earlycon enabled when it shouldn't be.

But this happens only when both "earlycon" and "console=" parameters
are used together. Do I get it correctly?

This combination is ambiguous on its own. Why would anyone add
"earlycon" parameter and wanted to keep it disabled?

> > >>> diff --git a/init/main.c b/init/main.c
> > >>> index aa21add5f7c54..f72bf644910c1 100644
> > >>> --- a/init/main.c
> > >>> +++ b/init/main.c
> > >>> @@ -738,8 +738,7 @@ static int __init do_early_param(char *param, char *val,
> > >>>       for (p = __setup_start; p < __setup_end; p++) {
> > >>>           if ((p->early && parameq(param, p->str)) ||
> > >>>               (strcmp(param, "console") == 0 &&
> > >>> -             strcmp(p->str, "earlycon") == 0)
> > >>> -        ) {
> > >>> +             strcmp(p->str, "earlycon") == 0 && val && val[0])) {
> > >>>               if (p->setup_func(val) != 0)
> > >>>                   pr_warn("Malformed early option '%s'\n", param);
> > >>>           }

Huh, this is getting more and more complicated.

You know, it is already bad that:

    + "console" enables the default console which might be overridden
      by ACPI SPCR and devicetree

    + "console=" causes that "ttynull" console is preferred,
	  it might cause that no console is registered at all

    + both "earlyconsole" and "earlyconsole=" cause that
          
     consoles is enabled 
   

It is already bad that "earlycon" and "console" handle the empty value
a different way. But this makes it even worse. The behaviour
would depend on a subtle difference whether "console" or
"console=" is used.



> > >>
> > >
> >
> > --
> > ~Randy