Message-ID: <CAHQZ30DjZE6Mg-KUrLQOLHh+OxNHZXRDkuZopxJb3F7G29TsXA@mail.gmail.com>
Date:   Fri, 14 Jul 2023 11:21:09 -0600
From:   Raul Rangel <rrangel@...omium.org>
To:     Petr Mladek <pmladek@...e.com>
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 Fri, Jul 14, 2023 at 10:38 AM Petr Mladek <pmladek@...e.com> wrote:
>
> 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.

It took a bit of digging to figure out what the actual intention was :)

>
> > 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?

The bug shows up when an SPCR table is present and the `console=`
parameter is set. No need to specify `earlycon` on the command line.

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

This is not the case I'm hitting. I'm honestly not sure what the
behavior should be in the `earlycon console=` case?

>
> > > >>> 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

That's what this patch fixes. You need to specify `earlycon` in order
to get the ACPI SPCR or DT console.

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

This patch also makes it so `console=` no longer enables the earlycon.

>
>     + 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.

This patch makes it so that `console` or `console=` don't enable
earlycon. Earlycon can only be enabled via `earlycon` or `earlycon=`.

I don't see the `console` (without the =) documented:
https://www.kernel.org/doc/html/v6.1/admin-guide/kernel-parameters.html.
I'm guessing this is an undocumented "feature" that snuck in while the
`earlycon` stuff was being added.

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

Thanks for reviewing,
Raul

Powered by blists - more mailing lists