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

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

[Guillaume Tucker]

On 12/10/2020 04:58, Willy Tarreau wrote:
> Hi Enric,
> 
> On Sun, Oct 11, 2020 at 07:05:55PM +0200, Enric Balletbo i Serra wrote:
>> For arm64 (i.e : arm64_defconfig):
>>     1. Someone renames CONFIG_A to CONFIG_AB, sends a patch, and as he did a
>> grep, the patch modifies all the defconfigs.
>>     2. The patch is accepted and merged in linux-next.
>>     3. KernelCI builds linux-next, boots the kernel on the hardware and all the
>> tests continue passing.
>>
>>
>> For x86:
>>     1. Someone renames CONFIG_A to CONFIG_AB, sends a patch and as he did a grep
>> the patches modifies all the defconfigs.
>>     2. The patch is accepted and merged in linux-next.
>>     3. KernelCI builds linux-next, boots the kernel on the hardware, and some
>> tests start to fail or are skipped.
>>     4. The maintainer is noticed about the behavior change, so he will need to
>> look at the problem, and find it.
>>     5. The maintainer sends a patch.
>>     6. The patch is accepted, but he needs to tag the release as per kernel <
>> x.y.z version it should use CONFIG_A and for kernel > x.y.z it should pick
>> CONFIG_AB.
>>     7. KernelCI builds linux-next, boots the kernel on the hardware and all the
>> tests pass again.
> 
> Previously I thought I understood your needs, but now I don't anymore. You
> seem to be saying that you're not testing *anything* outside of defconfig,
> and that as such you'd like defconfig to be complete enough to provide good
> coverage. This sounds a bit odd to me. And what if in the arm64 case, the
> CONFIG_YOUR_V4L2_DEVICE is *not* added to defconfig ? You're in the same
> situation.
> 
> We all know it's not fun to have to deal with local config snippets, but
> as soon as you plan to boot on a specific hardware, this is unavoidable.
> Also, config symbols are rarely renamed. Most often they are moved under
> new entries (e.g. CONFIG_VENDOR_FOO) which are enabled by default, so
> that updating your old configuration using "make olddefconfig" is enough
> to update it.
> 
> What I'm understanding from your proposed change is not to support
> KernelCI, but to support Chromebooks by default. This could make more
> sense if that's a relevant platform whose support is currently limited
> by default, I'm not able to judge that, but at least it seems to me
> this would make more sense than having specific configs for KernelCI.

This is correct, KernelCI doesn't really need these configs to be
upstreamed.  It's useful as Enric pointed out, but there are
already several specific config fragments being managed by the
KernelCI build system as one would expect, and we can take care
of one more if need be.

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.  That is what this patch is really about.  When doing
upstream kernel development and building your own kernel, it is
obviously a very useful thing to have.

Agreed, it is easy enough for a developer to turn these configs
on when required.  But it's not entirely trivial to find out
which configs to turn on, especially when you don't have access
to the kernel log.  I went through the Chrome OS 4.14 kernel
config fragments to get there.  Everyone would probably not
agree, but it does seem to me that the convenience of having it
upstream outweighs the costs.

If it's about size or performance, anyone can compare the kernel
image sizes and other things with the KernelCI (staging) build
artifacts based on v5.9[2].

As mentioned earlier in this thread, there aren't any written
rules about what goes into x86_64_defconfig and what does not.
Based on past history, and looking at it from a developer's point
of view rather than KernelCI, does it make sense in this case?

Thanks,
Guillaume


[1] HP Intel x360 "octopus" and AMD 11A-G6-EE "grunt":
    https://staging.kernelci.org/test/plan/id/5f8101a97ba4fdae00cafbb0/
    https://staging.kernelci.org/test/plan/id/5f81003f56c3586920cafbb4/

[2] Plain x86_64_defconfig:
    https://storage.staging.kernelci.org/kernelci/staging-mainline/staging-mainline-20201011.0/x86_64/x86_64_defconfig/gcc-8/
    with "x86 Chromebook" fragment:
    https://storage.staging.kernelci.org/kernelci/staging-mainline/staging-mainline-20201011.0/x86_64/x86_64_defconfig+x86-chromebook/gcc-8/

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

[Borislav Petkov]

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. Or do they do some sort of
serial over USB emulation and this is something which only chromebooks
have?

Or is that how it is done:

https://www.chromium.org/chromium-os/how-tos-and-troubleshooting/serial-debugging-howto

?

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

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

[Willy Tarreau]

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.

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 :-/

Willy

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

[Guillaume Tucker]

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

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

[Borislav Petkov]

On Mon, Oct 12, 2020 at 04:40:40PM +0200, Willy Tarreau wrote:
> 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 :-/

Yah, with all those new features crap they add to modern laptops, you'd
think they put in a serial port for 2¢ but nope... ;-\

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

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

[Borislav Petkov]

On Mon, Oct 12, 2020 at 04:10:45PM +0100, Guillaume Tucker wrote:
> 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.

That sounds interesting, thanks for elaborating.

At the same time, you see how this setup is very hw-specific and not
really common and those options do not really belong in a defconfig but
in a kernelCI snippet, I'd say.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

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

[Nick Desaulniers]

On Mon, Oct 12, 2020 at 8:10 AM Guillaume Tucker
<guillaume.tucker@collabora.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