linux-kernel - Re: [PATCH v2] serial: kgdboc: Allow earlycon initialization to be deferred

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Date:   Thu, 30 Apr 2020 09:47:27 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Daniel Thompson <daniel.thompson@...aro.org>
Cc:     Jason Wessel <jason.wessel@...driver.com>,
        Sumit Garg <sumit.garg@...aro.org>,
        kgdb-bugreport@...ts.sourceforge.net, linux-serial@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Patch Tracking <patches@...aro.org>
Subject: Re: [PATCH v2] serial: kgdboc: Allow earlycon initialization to be deferred

Hi,

On Thu, Apr 30, 2020 at 9:18 AM Daniel Thompson
<daniel.thompson@...aro.org> wrote:
>
> Currently there is no guarantee that an earlycon will be initialized
> before kgdboc tries to adopt it. Almost the opposite: on systems
> with ACPI then if earlycon has no arguments then it is guaranteed that
> earlycon will not be initialized.
>
> This patch mitigates the problem by giving kgdboc_earlycon a second
> chance during console_init(). This isn't quite as good as stopping during
> early parameter parsing but it is still early in the kernel boot.
>
> Signed-off-by: Daniel Thompson <daniel.thompson@...aro.org>
> ---
>
> Notes:
>     v2: Simplified, more robust, runs earlier, still has Doug's
>         recent patchset as a prerequisite. What's not to like?
>
>     More specifically, based on feedback from Doug Anderson, I
>     have replaced the initial hacky implementation with a console
>     initcall.
>
>     I also made it defer more aggressively after realizing that both
>     earlycon and kgdboc_earlycon are handled as early parameters
>     (meaning I think the current approach relies on the ordering
>     of drivers/tty/serial/Makefile to ensure the earlycon is enabled
>     before kgdboc tries to adopt it).
>
>     Finally, my apologies to Jason and kgdb ML folks, who are seeing
>     this patch for the first time. I copied the original circulation
>     list from a patch that wasn't kgdb related and forgot to update.
>
>  drivers/tty/serial/kgdboc.c | 41 +++++++++++++++++++++++++++++++++++--
>  1 file changed, 39 insertions(+), 2 deletions(-)

Thanks, this looks great!

Reviewed-by: Douglas Anderson <dianders@...omium.org>