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From:   Doug Anderson <dianders@chromium.org>
Date:   Thu, 14 May 2020 09:34:26 -0700
Message-ID: <CAD=FV=X+t_Wg5KadZBTGHMSEXY3c-t6DZAtdaLXys31QJJpGGA@mail.gmail.com>
Subject: Re: [PATCH v4 00/12] kgdb: Support late serial drivers; enable early
 debug w/ boot consoles
To:     Daniel Thompson <daniel.thompson@linaro.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Will Deacon <will@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>
Cc:     Jason Wessel <jason.wessel@windriver.com>,
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        Frank Rowand <frowand.list@gmail.com>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        linux-serial@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Jiri Slaby <jslaby@suse.com>,
        kgdb-bugreport@lists.sourceforge.net,
        Sumit Garg <sumit.garg@linaro.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andy Gross <agross@kernel.org>, bp@alien8.de,
        Alexios Zavras <alexios.zavras@intel.com>,
        Allison Randal <allison@lohutok.net>,
        Andrew Morton <akpm@linux-foundation.org>,
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        "Eric W. Biederman" <ebiederm@xmission.com>,
        James Morse <james.morse@arm.com>,
        Juergen Gross <jgross@suse.com>,
        Krzysztof Kozlowski <krzk@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
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Hi,

On Thu, May 14, 2020 at 9:21 AM Daniel Thompson
<daniel.thompson@linaro.org> wrote:
>
> 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

I was hoping to get an Ack from Will or Catalin for my most recent
arm64 patch [1] and then it could land in your tree.  However, it
wouldn't be the end of the world if that landed later.  "kgdbwait"
would be broken if you used it together with "kgdb_earlycon" but
overall we'd still be in a better place than we were.


> and 8250/amba-pl011/qcom_geni_serial code
> could be applied independently of the kgdb changes

Right, that would be OK.  Nobody would actually be able to use
"kgdb_earlycon" until those landed but there would be no problem with
those two landing separately.


> (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.

It would be nice for it to be explicit, but "get_maintainer" says that
Greg KH is the maintainer of serial drivers.  Git log confirms that he
also has been the one landing changes to these files.  Early-on he
provided his Reviewed-by for the series as a whole, so he's aware of
it and maybe would be fine w/ the serial changes landing through the
kgdb tree?

Greg: is that correct?


> 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/ ).

It feels to me that the kgdb tree is the best destination for all
these patches if possible.


[1] https://lore.kernel.org/r/20200513160501.1.I0b5edf030cc6ebef6ab4829f8867cdaea42485d8@changeid

-Doug