serial: Refactor uart_flush_buffer() from uart_close()

In the context of the final tty & port close, flushing the tx
ring buffer after the hardware has already been shutdown and
the ring buffer freed is neither required nor desirable.

uart_flush_buffer() performs 3 operations:
1. Resets tx ring buffer indices, but the tx ring buffer has
   already been freed and the indices are reset if the port is
   re-opened.
2. Calls uart driver's flush_buffer() method
   5 in-tree uart drivers define flush_buffer() methods:
     amba-pl011, atmel-serial, imx, serial-tegra, timbuart
   These have been refactored into the shutdown() method, if
   required.
3. Kicks the ldisc for more writing, but this is undesirable.
   The file handle is being released; any waiting writer will
   will be kicked out by tty_release() with a warning. Further,
   the N_TTY ldisc may generate SIGIO for a file handle which
   is no longer valid.

Cc: Nicolas Ferre <nicolas.ferre@atmel.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 16 insertions, 14 deletions

diff --git a/drivers/tty/serial/serial-tegra.c b/drivers/tty/serial/serial-tegra.c
index 53d7c31ce098..78a5cf65bf02 100644
--- a/drivers/tty/serial/serial-tegra.c
+++ b/drivers/tty/serial/serial-tegra.c
@@ -1034,6 +1034,20 @@ fail_rx_dma:
 	return ret;
 }
 
+/*
+ * Flush any TX data submitted for DMA and PIO. Called when the
+ * TX circular buffer is reset.
+ */
+static void tegra_uart_flush_buffer(struct uart_port *u)
+{
+	struct tegra_uart_port *tup = to_tegra_uport(u);
+
+	tup->tx_bytes = 0;
+	if (tup->tx_dma_chan)
+		dmaengine_terminate_all(tup->tx_dma_chan);
+	return;
+}
+
 static void tegra_uart_shutdown(struct uart_port *u)
 {
 	struct tegra_uart_port *tup = to_tegra_uport(u);
@@ -1046,6 +1060,8 @@ static void tegra_uart_shutdown(struct uart_port *u)
 	tegra_uart_dma_channel_free(tup, true);
 	tegra_uart_dma_channel_free(tup, false);
 	free_irq(u->irq, tup);
+
+	tegra_uart_flush_buffer(u);
 }
 
 static void tegra_uart_enable_ms(struct uart_port *u)
@@ -1174,20 +1190,6 @@ static void tegra_uart_set_termios(struct uart_port *u,
 	return;
 }
 
-/*
- * Flush any TX data submitted for DMA and PIO. Called when the
- * TX circular buffer is reset.
- */
-static void tegra_uart_flush_buffer(struct uart_port *u)
-{
-	struct tegra_uart_port *tup = to_tegra_uport(u);
-
-	tup->tx_bytes = 0;
-	if (tup->tx_dma_chan)
-		dmaengine_terminate_all(tup->tx_dma_chan);
-	return;
-}
-
 static const char *tegra_uart_type(struct uart_port *u)
 {
 	return TEGRA_UART_TYPE;