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List:       linux-rt-users
Subject:    Re: printk: console output corrupted
From:       John Ogness <john.ogness () linutronix ! de>
Date:       2023-02-21 16:14:48
Message-ID: 87bklnro9j.fsf () jogness ! linutronix ! de
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Hi Andre,

On 2023-02-21, André Pribil <Andre.Pribil@hms-networks.com> wrote:
> I'm using a IMX8MP board with kernel 5.10.165-rt81. UART3 is used as
> the console device.  When the device boots the serial outputs on this
> UART get corrupted at some point.  It looks like only one line is
> corrupted. However, this line often confuses my terminal, so that the
> lines behind are also not shown correctly. A reset of the terminal
> fixes that.
>
> I could not figure out why this happens, yet. I only know that the
> issue does not occur when I remove the preempt-rt patch or when I
> specify the "maxcpus=1" kernel command line parameter. I also tried to
> enable/disable the "earlycon" setting, but this seem to only change
> the time when this happens during the boot messages.
>
> When the boot messages are afterwards displayed with "dmesg", they do
> not contain corrupted characters. Therefore, I assume that the
> corruption occurs at the UART level.  Maybe some lock issue and
> therefore some concurrent access to the UART registers?

There is a known problem [0] with this printk implementation that it
does not support boot consoles. I will follow-up this email with the
rebased patch from Petr Mladek, which should work around the
issue. Please check if it works for you.

John Ogness

[0] https://lore.kernel.org/lkml/YrCO04oNncE1xF5K@alley
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