Re: [PATCH 03/26] serial: altera_uart: drop low-latency workaround

Tobias Klauser
2021-04-21T10:12:00Z

On 2021-04-21 at 11:54:46 +0200, Johan Hovold <johan@kernel.org> wrote:
> Commit dd085ed8ef6c ("tty: serial: altera: drop uart_port->lock before
> calling tty_flip_buffer_push()") claimed to address a locking
> issue but only provided a dubious lockdep splat from an unrelated
> driver, which in the end turned out to be due a broken local change
> carried by the author.
>
> Unfortunately these patches were merged before the issue had been
> analysed properly so the commit messages makes no sense whatsoever.
>
> The real issue was first seen on RT which at the time effectively always
> set the low_latency flag for all serial drivers by patching
> tty_flip_buffer_push(). This in turn revealed that many drivers did not
> handle the infamous low_latency behaviour which meant that data was
> pushed immediately to the line discipline instead of being deferred to a
> work queue.
>
> Since commit a9c3f68f3cd8 ("tty: Fix low_latency BUG"),
> tty_flip_buffer_push() always schedules a work item to push data to the
> line discipline and there's no need to keep any low_latency hacks
> around.
>
> Link: https://lore.kernel.org/linux-serial/cover.1376923198.git.viresh.kumar@linaro.org/
> Cc: Tobias Klauser <tklauser@distanz.ch>
> Signed-off-by: Johan Hovold <johan@kernel.org>

Acked-by: Tobias Klauser <tklauser@distanz.ch>

Thanks