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From:   Doug Anderson <dianders@chromium.org>
Date:   Mon, 6 May 2019 16:58:29 -0700
Message-ID: <CAD=FV=WcjfUwH62bHVELOmzViv7d329r6+HfPqAyXMjKCO7LeQ@mail.gmail.com>
Subject: Re: [PATCH] pstore/ram: Improve backward compatibility with older Chromebooks
To:     Kees Cook <keescook@chromium.org>
Cc:     Rob Herring <robh@kernel.org>, Anton Vorontsov <anton@enomsg.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@lists.infradead.org>,
        Julius Werner <jwerner@chromium.org>,
        Guenter Roeck <groeck@chromium.org>,
        Matthias Kaehlcke <mka@chromium.org>,
        Brian Norris <briannorris@chromium.org>,
        Colin Cross <ccross@android.com>,
        Tony Luck <tony.luck@intel.com>,
        LKML <linux-kernel@vger.kernel.org>
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Hi,

On Mon, May 6, 2019 at 2:10 PM Kees Cook <keescook@chromium.org> wrote:
>
> From: Douglas Anderson <dianders@chromium.org>
> Date: Fri, May 3, 2019 at 10:48 AM
> To: Kees Cook, Anton Vorontsov
> Cc: <linux-rockchip@lists.infradead.org>, <jwerner@chromium.org>,
> <groeck@chromium.org>, <mka@chromium.org>, <briannorris@chromium.org>,
> Douglas Anderson, Colin Cross, Tony Luck,
> <linux-kernel@vger.kernel.org>
>
> > When you try to run an upstream kernel on an old ARM-based Chromebook
> > you'll find that console-ramoops doesn't work.
> >
> > Old ARM-based Chromebooks, before <https://crrev.com/c/439792>
> > ("ramoops: support upstream {console,pmsg,ftrace}-size properties")
> > used to create a "ramoops" node at the top level that looked like:
> >
> > / {
> >   ramoops {
> >     compatible = "ramoops";
> >     reg = <...>;
> >     record-size = <...>;
> >     dump-oops;
> >   };
> > };
> >
> > ...and these Chromebooks assumed that the downstream kernel would make
> > console_size / pmsg_size match the record size.  The above ramoops
> > node was added by the firmware so it's not easy to make any changes.
> >
> > Let's match the expected behavior, but only for those using the old
> > backward-compatible way of working where ramoops is right under the
> > root node.
> >
> > NOTE: if there are some out-of-tree devices that had ramoops at the
> > top level, left everything but the record size as 0, and somehow
> > doesn't want this behavior, we can try to add more conditions here.
> >
> > Signed-off-by: Douglas Anderson <dianders@chromium.org>
>
> I like this; thanks! Rob is this okay by you? I just want to
> double-check since it's part of the DT parsing logic.
>
> I'll pick it up and add a Cc: stable.

Hold off a second--I may need to send out a v2 but out of time for the
day.  I think I need a #include file to fix errors on x86:

> implicit declaration of function 'of_node_is_root' [-Werror,-Wimplicit-function-declaration

I'm unfortunately out of time for now, but I'll post a v2 within the next day.


-Doug