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Message-ID: <cae5cf32-4ad1-0dbf-1b61-c57dd5549798@infradead.org>
Date: Mon, 10 Jul 2023 08:41:41 -0700
From: Randy Dunlap <rdunlap@...radead.org>
To: Raul Rangel <rrangel@...omium.org>
Cc: Mario Limonciello <mario.limonciello@....com>,
linux-kernel@...r.kernel.org,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Petr Mladek <pmladek@...e.com>, 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
Hi,
On 7/10/23 08:30, 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=
[many lines deleted here in kernel-parameters.txt]
> { 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.
>
OK, I see what you are referring to: "console=" without any following parameters,
not the general "console=" command line parameter.
Thanks for the clarification.
> 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.
>
> 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.
>
>>> I read that as "it's intention is to disable the default console (tty0)".
>>
>> Yes, that "default" word should be there IMO.
>>
>> Does this patch affect behavior if someone uses
>> console=tty0
>> i.e., the default?
>>
>
> No, it shouldn't. This change makes it so that the
> param_setup_earlycon function gets
> skipped if there is no value.
> See https://chromium.googlesource.com/chromiumos/third_party/kernel/+/v6.1/drivers/tty/serial/earlycon.c#223
--
~Randy
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