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

[Jon Hunter <jonathanh@nvidia.com>]

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@linutronix.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

-- 
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