From c0a6c9f79e5266d750b73bff5a61761827f4687d Mon Sep 17 00:00:00 2001 From: Johan Hovold Date: Wed, 21 Apr 2021 11:54:59 +0200 Subject: serial: msm_serial: drop low-latency workaround Commit f77232dab25b ("tty: serial: msm: 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: Andy Gross Cc: Bjorn Andersson Acked-by: Bjorn Andersson Signed-off-by: Johan Hovold Link: https://lore.kernel.org/r/20210421095509.3024-17-johan@kernel.org Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/msm_serial.c | 4 ---- 1 file changed, 4 deletions(-) (limited to 'drivers/tty') diff --git a/drivers/tty/serial/msm_serial.c b/drivers/tty/serial/msm_serial.c index 770c182e2208..fcef7a961430 100644 --- a/drivers/tty/serial/msm_serial.c +++ b/drivers/tty/serial/msm_serial.c @@ -757,9 +757,7 @@ static void msm_handle_rx_dm(struct uart_port *port, unsigned int misr) count -= r_count; } - spin_unlock(&port->lock); tty_flip_buffer_push(tport); - spin_lock(&port->lock); if (misr & (UART_IMR_RXSTALE)) msm_write(port, UART_CR_CMD_RESET_STALE_INT, UART_CR); @@ -819,9 +817,7 @@ static void msm_handle_rx(struct uart_port *port) tty_insert_flip_char(tport, c, flag); } - spin_unlock(&port->lock); tty_flip_buffer_push(tport); - spin_lock(&port->lock); } static void msm_handle_tx_pio(struct uart_port *port, unsigned int tx_count) -- cgit v1.2.3