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

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Date:   Sun, 9 Jul 2023 19:43:36 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Mario Limonciello <mario.limonciello@....com>,
        Raul E Rangel <rrangel@...omium.org>,
        linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Petr Mladek <pmladek@...e.com>
Cc:     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 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)?
> 
> 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?

> 
> IE if I add console=ttyS0,115200,n8 to my kernel command line then I don't get the output on tty0 anymore.  If I want it on both then I do
> 
> console=ttyS0,115200,n8 console=tty0.
> 
>>
>>> flag to the earlycon handler, we enable the earlycon_acpi_spcr_enable
>>> variable when an SPCR table is present. This means that we
>>> inadvertently enable the earlycon.
>>>
>>> This change makes it so we only proxy the console= command if it's
>>> value is not empty. This way we can correctly handle both cases.
>>>
>>> Signed-off-by: Raul E Rangel <rrangel@...omium.org>
>>> ---
>>>
>>>   init/main.c | 3 +--
>>>   1 file changed, 1 insertion(+), 2 deletions(-)
>>>
>>> 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);
>>>           }
>>
> 

-- 
~Randy