linux-kernel - Re: [RFC PATCH] tty: serial: kgdboc: Fix 8250

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Message-ID: <CAOf5uw=6=zNmtVU7cOWv6xTaCghvX9j8pA9ijJxEqYpzikGdcg@mail.gmail.com>
Date:   Tue, 12 Dec 2023 09:54:24 +0100
From:   Michael Nazzareno Trimarchi <michael@...rulasolutions.com>
To:     Doug Anderson <dianders@...omium.org>
Cc:     Jason Wessel <jason.wessel@...driver.com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        kgdb-bugreport@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        linux-serial@...r.kernel.org
Subject: Re: [RFC PATCH] tty: serial: kgdboc: Fix 8250_* kgd over serial

Hi Doug

On Mon, Dec 11, 2023 at 11:00 PM Doug Anderson <dianders@...omium.org> wrote:
>
> Hi,
>
> On Mon, Dec 11, 2023 at 1:42 PM Michael Nazzareno Trimarchi
> <michael@...rulasolutions.com> wrote:
> >
> > > 1. init_kgdboc() runs and registers the singleton kgdb "platform driver".
> > >
> > > 2. The platform driver's probe function, kgdboc_probe(), runs and
> > > checks to see if the console is ready by looking at the return value
> > > of configure_kgdboc(). If it's ready then we're good to go. If it's
> > > not ready then we defer.
> > >
> > > So I think the bug here is that somehow the console looks "ready"
> > > (because tty_find_polling_driver() can find it) but it isn't actually
> > > ready yet (because it crashes). That's what you need to fix.
> > >
> >
> > The polling driver look for uart and uart8250_core is registered and 4 fake uart
> > are there but there are not still replaced by platform driver that can
> > come later.
> > The try_polling find it but it's the isa-8250 driver. It means that
> > add_uart 8250 is
> > not still happen
>
> The 8250 driver is always a maze, so you might need to do a bunch of
> digging. ...but it sure sounds like the console shouldn't be
> registered until the correct ops are in place. That either means
> getting the ops put in place earlier or deferring when the console is
> registered...
>

Your point is pretty clear and my initial idea was to find a real fix.
This come to avoid
breaking existing setup but anyway I will dig in it more

Michael

> -Doug



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Michael Nazzareno Trimarchi
Co-Founder & Chief Executive Officer
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