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SubjectRe: [RFC][PATCH] x86: Allow early_printk to use console style param like 115200n8

* Steven Rostedt <rostedt@goodmis.org> wrote:

> When I enable early_printk on a kernel, I cut and paste the console=
> input and add to earlyprintk parameter. But I notice recently that
> ktest has not been detecting triple faults. The way it detects it, is
> by seeing the kernel banner "Linux version .." with a different kernel
> version pop up. Then I noticed that early printk was no longer working
> on my console, which was why ktest was not seeing it.
>
> I bisected it down and it was added to 4.0 with this commit:
>
> commit ea9e9d802902 ("Specify PCI based UART for earlyprintk")

Ugh, this commit changed x86 code but was not Cc:-ed to any x86 maintainer, and
the title was pretty misleading as well...

( That patch should have been split into at least two parts: the generic
earlyprintk changes affecting all modes, and the 'pciserial' enablement. Anyway,
that's water down the bridge. )

> because it converted the simple_strtoul() that converts the baud number into a
> kstrtoul(). The problem with this is, I had as my baud rate, 115200n8
> (acceptable for console=ttyS0), but because of the "n8", the kstrtoul() doesn't
> parse the baud rate and returns an error, which sets the baud rate to the
> default 9600. This explains the garbage on my screen.

ugh. I bet it also breaks the earlyprintk=ttyS0..,keep format?

> Now, earlyprintk= kernel parameter does not say it accepts that format. Thus,
> one answer would simply be me changing my kernel parameters to remove the "n8"
> since it isn't parsed anyway. But I wonder if other people run into this, and it
> seems strange that the two consoles for serial accepts different input.

So why not revert to the known-working simple_strtoul()? I don't see this as an
improvement:

> + /*
> + * In case the input is like console with text after the baud
> + * rate. e.g. 115200n8. kstrtoul() will error on such input.
> + */
> + for (p = s; *p && isdigit(*p); p++)
> + ;
> + *p = 0;
> +
> if (kstrtoul(s, 0, &baud) < 0 || baud == 0)
> baud = DEFAULT_BAUD;


Over the old:

baud = simple_strtoul(s, &e, 0);

Thanks,

Ingo


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