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From nobody Mon Sep 17 00:00:00 2001
From: Håvard Skinnemoen <hskinnemoen@atmel.com>
Date: Thu Feb 2 15:48:50 2006 +0100
Subject: [PATCH] Add flush_buffer() operation to uart_ops

Serial drivers using DMA (like the Atmel USART3 driver) tend to get
very confused when the xmit buffer is flushed and nobody told them.
They also tend to spew a lot of garbage since the DMA engine keeps
running after the buffer is flushed and possibly refilled with
unrelated data.

This patch adds a new flush_buffer operation to the uart_ops struct,
along with a call to it from uart_flush_buffer() right after the xmit
buffer has been cleared. The driver can implement this in order to
syncronize its internal DMA state with the xmit buffer when the buffer
is flushed.

---

 Documentation/serial/driver  |   11 +++++++++++
 drivers/serial/serial_core.c |    2 ++
 include/linux/serial_core.h  |    1 +
 3 files changed, 14 insertions(+)

Index: linux-2.6.16-avr32/Documentation/serial/driver
===================================================================
--- linux-2.6.16-avr32.orig/Documentation/serial/driver	2006-03-20 06:53:29.000000000 +0100
+++ linux-2.6.16-avr32/Documentation/serial/driver	2006-04-03 18:57:11.000000000 +0200
@@ -186,6 +186,17 @@ hardware.
 	Locking: port_sem taken.
 	Interrupts: caller dependent.
 
+  flush_buffer(port)
+	Flush any write buffers, reset any DMA state and stop any
+	ongoing DMA transfers.
+
+	This will be called whenever the port->info->xmit circular
+	buffer is cleared.
+
+	Locking: port->lock taken.
+	Interrupts: locally disabled.
+	This call must not sleep
+
   set_termios(port,termios,oldtermios)
 	Change the port parameters, including word length, parity, stop
 	bits.  Update read_status_mask and ignore_status_mask to indicate
Index: linux-2.6.16-avr32/drivers/serial/serial_core.c
===================================================================
--- linux-2.6.16-avr32.orig/drivers/serial/serial_core.c	2006-03-20 06:53:29.000000000 +0100
+++ linux-2.6.16-avr32/drivers/serial/serial_core.c	2006-04-03 18:57:11.000000000 +0200
@@ -556,6 +556,8 @@ static void uart_flush_buffer(struct tty
 
 	spin_lock_irqsave(&port->lock, flags);
 	uart_circ_clear(&state->info->xmit);
+	if (port->ops->flush_buffer)
+		port->ops->flush_buffer(port);
 	spin_unlock_irqrestore(&port->lock, flags);
 	tty_wakeup(tty);
 }
Index: linux-2.6.16-avr32/include/linux/serial_core.h
===================================================================
--- linux-2.6.16-avr32.orig/include/linux/serial_core.h	2006-03-20 06:53:29.000000000 +0100
+++ linux-2.6.16-avr32/include/linux/serial_core.h	2006-04-03 18:57:11.000000000 +0200
@@ -164,6 +164,7 @@ struct uart_ops {
 	void		(*break_ctl)(struct uart_port *, int ctl);
 	int		(*startup)(struct uart_port *);
 	void		(*shutdown)(struct uart_port *);
+	void		(*flush_buffer)(struct uart_port *);
 	void		(*set_termios)(struct uart_port *, struct termios *new,
 				       struct termios *old);
 	void		(*pm)(struct uart_port *, unsigned int state,