linux-kernel - Re: [PATCH v4 00/12] kgdb: Support late serial drivers; enable early debug w/ boot consoles

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Message-ID: <20200514162109.6qt5drd27hpilijh@holly.lan>
Date:   Thu, 14 May 2020 17:21:09 +0100
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     jason.wessel@...driver.com, gregkh@...uxfoundation.org,
        corbet@....net, frowand.list@...il.com, bjorn.andersson@...aro.org,
        linux-serial@...r.kernel.org, mingo@...hat.com, hpa@...or.com,
        jslaby@...e.com, kgdb-bugreport@...ts.sourceforge.net,
        sumit.garg@...aro.org, will@...nel.org, tglx@...utronix.de,
        agross@...nel.org, catalin.marinas@....com, bp@...en8.de,
        Alexios Zavras <alexios.zavras@...el.com>,
        Allison Randal <allison@...utok.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Martin <Dave.Martin@....com>,
        Enrico Weigelt <info@...ux.net>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        James Morse <james.morse@....com>,
        Juergen Gross <jgross@...e.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Russell King <linux@...linux.org.uk>,
        jinho lim <jordan.lim@...sung.com>,
        linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v4 00/12] kgdb: Support late serial drivers; enable early
 debug w/ boot consoles

On Thu, May 07, 2020 at 01:08:38PM -0700, Douglas Anderson wrote:
> <snip>
>
> My first attempt was to try to get the existing "ekgdboc" to work
> earlier.  I tried that for a bit until I realized that it needed to
> work at the tty layer and I couldn't find any serial drivers that
> managed to register themselves to the tty layer super early at boot.
> The only documented use of "ekgdboc" is "ekgdboc=kbd" and that's a bit
> of a special snowflake.  Trying to get my serial driver and all its
> dependencies to probe normally and register the tty driver super early
> at boot seemed like a bad way to go.  In fact, all the complexity
> needed to do something like this is why the system already has a
> special concept of a "boot console" that lives only long enough to
> transition to the normal console.
> 
> <snip>
> 
> The devices I had for testing were:
> - arm32: rk3288-veyron-jerry
> - arm64: rk3399-gru-kevin
> - arm64: qcom-sc7180-trogdor (not mainline yet)
> 
> These are the devices I tested this series on.  I tried to test
> various combinations of enabling/disabling various options and I
> hopefully caught the corner cases, but I'd appreciate any extra
> testing people can do.  Notably I didn't test on x86, but (I think) I
> didn't touch much there so I shouldn't have broken anything.

I have tested a slightly earlier version using qemu and will test this
set before it moves forwards.


>  .../admin-guide/kernel-parameters.txt         |  20 ++
>  Documentation/dev-tools/kgdb.rst              |  24 ++
>  arch/arm64/Kconfig                            |   1 +
>  arch/arm64/include/asm/debug-monitors.h       |   2 +
>  arch/arm64/kernel/debug-monitors.c            |   2 +-
>  arch/arm64/kernel/traps.c                     |   3 +
>  arch/x86/Kconfig                              |   1 +
>  drivers/tty/serial/8250/8250_early.c          |  23 ++
>  drivers/tty/serial/amba-pl011.c               |  32 +++
>  drivers/tty/serial/kgdboc.c                   | 268 ++++++++++++++++--
>  drivers/tty/serial/qcom_geni_serial.c         |  32 +++
>  include/linux/kgdb.h                          |   4 +
>  kernel/debug/debug_core.c                     |  52 +++-
>  lib/Kconfig.kgdb                              |  18 ++
>  14 files changed, 436 insertions(+), 46 deletions(-)

Any thoughts on how best to land these changes?

AFAICT the arm64 and 8250/amba-pl011/qcom_geni_serial code
could be applied independently of the kgdb changes (though we must keep
changes to drivers/tty/serial/kgdboc alongside the kgdb changes).

I can hoover them up but I'd need a solid set of acks and
I don't think we've got that yet.

I'd also be happy to ack where needed and let someone else pick it up
(the other changes queued for kgdb this cycle are pretty small so we
shouldn't see much conflict in kernel/debug/ ).


Daniel.