From d0aa2820b9e85e79f5a76eb7874316aaa04bdff9 Mon Sep 17 00:00:00 2001 From: Johan Hovold Date: Wed, 21 Apr 2021 11:54:49 +0200 Subject: [PATCH] serial: apbuart: drop low-latency workaround Commit 78d34d75c84d ("tty: serial: apbuart: 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/ Signed-off-by: Johan Hovold Link: https://lore.kernel.org/r/20210421095509.3024-7-johan@kernel.org Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/apbuart.c | 2 -- 1 file changed, 2 deletions(-) diff --git a/drivers/tty/serial/apbuart.c b/drivers/tty/serial/apbuart.c index e8d56e899ec7..d8c937bdf3f9 100644 --- a/drivers/tty/serial/apbuart.c +++ b/drivers/tty/serial/apbuart.c @@ -117,9 +117,7 @@ static void apbuart_rx_chars(struct uart_port *port) status = UART_GET_STATUS(port); } - spin_unlock(&port->lock); tty_flip_buffer_push(&port->state->port); - spin_lock(&port->lock); } static void apbuart_tx_chars(struct uart_port *port)