linux-kernel - Re: [PATCH tty-next v5 5/6] serial: 8250: Switch to nbcon console

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Message-ID: <80b020fc-c18a-4da4-b222-16da1cab2f4c@nvidia.com>
Date: Wed, 15 Jan 2025 16:21:28 +0000
From: Jon Hunter <jonathanh@...dia.com>
To: John Ogness <john.ogness@...utronix.de>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Jiri Slaby <jirislaby@...nel.org>, Petr Mladek <pmladek@...e.com>,
 Sergey Senozhatsky <senozhatsky@...omium.org>,
 Steven Rostedt <rostedt@...dmis.org>, Thomas Gleixner <tglx@...utronix.de>,
 Esben Haabendal <esben@...nix.com>, linux-serial@...r.kernel.org,
 linux-kernel@...r.kernel.org,
 Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 Arnd Bergmann <arnd@...db.de>, Tony Lindgren <tony@...mide.com>,
 Niklas Schnelle <schnelle@...ux.ibm.com>,
 Serge Semin <fancer.lancer@...il.com>,
 "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH tty-next v5 5/6] serial: 8250: Switch to nbcon console

Hi John,

On 07/01/2025 21:27, John Ogness wrote:
> Implement the necessary callbacks to switch the 8250 console driver
> to perform as an nbcon console.
> 
> Add implementations for the nbcon console callbacks:
> 
>    ->write_atomic()
>    ->write_thread()
>    ->device_lock()
>    ->device_unlock()
> 
> and add CON_NBCON to the initial @flags.
> 
> All register access in the callbacks are within unsafe sections.
> The ->write_atomic() and ->write_thread() callbacks allow safe
> handover/takeover per byte and add a preceding newline if they
> take over from another context mid-line.
> 
> For the ->write_atomic() callback, a new irq_work is used to defer
> modem control since it may be called from a context that does not
> allow waking up tasks.
> 
> Note: A new __serial8250_clear_IER() is introduced for direct
> clearing of UART_IER. This will allow to restore the lockdep
> check to serial8250_clear_IER() in a follow-up commit.
> 
> Signed-off-by: John Ogness <john.ogness@...utronix.de>


I have noticed a suspend regression on -next for some of our 32-bit 
Tegra (ARM) devices (Tegra20, Tegra30 and Tegra124). Bisect is pointing 
to this commit and reverting this on top of -next (along with reverting 
"serial: 8250: Revert "drop lockdep annotation from 
serial8250_clear_IER()") fixes the issue. So far I have not dug in any 
further. Unfortunately, I don't have any logs to see if there is some 
crash or something happening but I will see if there is any more info I 
can get.

Thanks
Jon

-- 
nvpublic