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   is no longer valid.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, 15 insertions, 13 deletions

diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
index edde3ec..8a84034 100644
--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c
@@ -1802,6 +1802,20 @@ free_irq:
 }
 
 /*
+ * Flush any TX data submitted for DMA. Called when the TX circular
+ * buffer is reset.
+ */
+static void atmel_flush_buffer(struct uart_port *port)
+{
+	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
+
+	if (atmel_use_pdc_tx(port)) {
+		UART_PUT_TCR(port, 0);
+		atmel_port->pdc_tx.ofs = 0;
+	}
+}
+
+/*
  * Disable the port
  */
 static void atmel_shutdown(struct uart_port *port)
@@ -1852,20 +1866,8 @@ static void atmel_shutdown(struct uart_port *port)
 	atmel_free_gpio_irq(port);
 
 	atmel_port->ms_irq_enabled = false;
-}
 
-/*
- * Flush any TX data submitted for DMA. Called when the TX circular
- * buffer is reset.
- */
-static void atmel_flush_buffer(struct uart_port *port)
-{
-	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
-
-	if (atmel_use_pdc_tx(port)) {
-		UART_PUT_TCR(port, 0);
-		atmel_port->pdc_tx.ofs = 0;
-	}
+	atmel_flush_buffer(port);
 }
 
 /*