imx-serial: RX DMA startup latency (4dec2f11) · Commits · 戴 / test

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 <peter.senna@collabora.com> Tested-by:

Sascha Hauer <s.hauer@pengutronix.de> Signed-off-by:

Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/imx.c

+5 −21

Original line number	Diff line number	Diff line
		@@ -1340,30 +1340,14 @@ 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);
		}
		}

		spin_unlock_irqrestore(&sport->port.lock, flags);

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