From 4dec2f119e86f9c91e60cdd8f0cc057452e331a9 Mon Sep 17 00:00:00 2001 From: Peter Senna Tschudin Date: Sun, 14 May 2017 14:35:15 +0200 Subject: [PATCH] imx-serial: RX DMA startup latency 18a4208 introduced a change to reduce the RX DMA latency on the first reception when the serial port was opened for reading. However it was claiming a hardirq unsafe lock after a hardirq safe lock which is not allowed and causes lockdep to complain verbosely. This patch changes the code to always start RX DMA earlier, instead of relying on the flags used to open the serial port removing the code that was looking for the serial file flags. Signed-off-by: Peter Senna Tschudin Tested-by: Sascha Hauer Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/imx.c | 26 +++++--------------------- 1 file changed, 5 insertions(+), 21 deletions(-) diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c index 33509b4beaec..64e16b37ebdb 100644 --- a/drivers/tty/serial/imx.c +++ b/drivers/tty/serial/imx.c @@ -1340,29 +1340,13 @@ static int imx_startup(struct uart_port *port) imx_enable_ms(&sport->port); /* - * If the serial port is opened for reading start RX DMA immediately - * instead of waiting for RX FIFO interrupts. In our iMX53 the average - * delay for the first reception dropped from approximately 35000 - * microseconds to 1000 microseconds. + * Start RX DMA immediately instead of waiting for RX FIFO interrupts. + * In our iMX53 the average delay for the first reception dropped from + * approximately 35000 microseconds to 1000 microseconds. */ if (sport->dma_is_enabled) { - struct tty_struct *tty = sport->port.state->port.tty; - struct tty_file_private *file_priv; - int readcnt = 0; - - spin_lock(&tty->files_lock); - - if (!list_empty(&tty->tty_files)) - list_for_each_entry(file_priv, &tty->tty_files, list) - if (!(file_priv->file->f_flags & O_WRONLY)) - readcnt++; - - spin_unlock(&tty->files_lock); - - if (readcnt > 0) { - imx_disable_rx_int(sport); - start_rx_dma(sport); - } + imx_disable_rx_int(sport); + start_rx_dma(sport); } spin_unlock_irqrestore(&sport->port.lock, flags);