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Commit 6bb0e3a5 authored by Haavard Skinnemoen's avatar Haavard Skinnemoen Committed by Linus Torvalds
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Subject: [PATCH 1/2] serial: Add flush_buffer() operation to uart_ops 



Serial drivers using DMA (like the atmel_serial 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.

Signed-off-by: default avatarHaavard Skinnemoen <haavard.skinnemoen@atmel.com>
Acked-by: default avatarAlan Cox <alan@redhat.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 15648f15

Documentation/serial/driver

+11 −0
Original line number Diff line number Diff line
@@ -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

drivers/serial/serial_core.c

+2 −0
Original line number Diff line number Diff line
@@ -573,6 +573,8 @@ static void uart_flush_buffer(struct tty_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);

}

include/linux/serial_core.h

+1 −0
Original line number Diff line number Diff line
@@ -190,6 +190,7 @@ 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 ktermios *new,

				       struct ktermios *old);

	void		(*set_ldisc)(struct uart_port *);