linux-kernel - Re: [PATCH] x86/x86_64_defconfig: Enable the serial console

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Date:   Mon, 12 Oct 2020 10:52:51 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     kernelci@...ups.io,
        Guillaume Tucker <guillaume.tucker@...labora.com>
Cc:     Willy Tarreau <w@....eu>, Borislav Petkov <bp@...en8.de>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Collabora Kernel ML <kernel@...labora.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Diego Elio Pettenò <flameeyes@...meeyes.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Nathan Chancellor <natechancellor@...il.com>
Subject: Re: [PATCH] x86/x86_64_defconfig: Enable the serial console

On Mon, Oct 12, 2020 at 8:10 AM Guillaume Tucker
<guillaume.tucker@...labora.com> wrote:
>
> On 12/10/2020 15:40, Willy Tarreau wrote:
> > On Mon, Oct 12, 2020 at 04:32:12PM +0200, Borislav Petkov wrote:
> >> On Mon, Oct 12, 2020 at 11:22:10AM +0100, Guillaume Tucker wrote:
> >>> However, it was found while adding some x86 Chromebooks[1] to
> >>> KernelCI that x86_64_defconfig lacked some basic things for
> >>> anyone to be able to boot a kernel with a serial console enabled
> >>> on those.
> >>
> >> Hold on, those are laptops, right? How come they do have serial console?
> >> Because laptops don't have serial console - that has been the eternal
> >> problem with debugging kernels on laptops.
>
> Yes the link you pointed at is a prerequisite to enable serial
> console in the firmware (Coreboot/Depthcharge).
>
> > Well, to be precise, they don't have *anymore*. I used to exclusively
> > select laptops having a serial port given that I was using it daily with
> > routers, until I had to resign when I abandonned my good old NC8000 :-/
>
> You can get serial console on recent enough Chromebooks with a
> debug interface such as SuzyQable:
>
>   https://www.sparkfun.com/products/14746
>
> It's not a USB Type-C adapter, it has a debug interface which
> works with Chromebooks that support Case-Closed Debugging.
> Anyone can do that without modifying the Chromebook, and with a
> bit of patience to go through the documentation[1]...
>
> The KernelCI sample results from my previous email were run using
> just that: off-the-shelf Chromebooks + SuzyQ + rebuilt firmware
> for interactive console and tftp boot + kernel with the config
> options in Enric's patch.
>
> Thanks,
> Guillaume
>
>
> [1] https://chromium.googlesource.com/chromiumos/platform/ec/+/cr50_stab/docs/case_closed_debugging_cr50.md

Thanks for the links, I've just now ordered one.  For the open case
debugging, we have some custom daughter board with a ribbon cable.
It's...not pretty.  I didn't know we had closed case debugging on
CrOS.

-- 
Thanks,
~Nick Desaulniers