diff mbox series

serial: mvebu-uart: fix tx lost characters

Message ID 3B588D51285A4A4D8D39C94212E07826278BDF@SPQCMBX02.exfo.com
State New
Headers show
Series serial: mvebu-uart: fix tx lost characters | expand

Commit Message

Gabriel Matni March 16, 2018, 1:45 p.m. UTC 
From: Gabriel Matni <gabriel.matni@exfo.com>


Fixes missing characters on kernel console at low baud rates (i.e.9600).
The driver should poll TX_RDY or TX_FIFO_EMP instead of TX_EMP to ensure
that the transmitter holding register (THR) is ready to receive a new byte.

TX_EMP tells us when it is possible to send a break sequence via
SND_BRK_SEQ. While this also indicates that both the THR and the TSR are
empty, it does not guarantee that a new byte can be written just yet.

Fixes: 30530791a7a0 ("serial: mvebu-uart: initial support for Armada-3700
      serial port")
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com> 

Acked-by: Gregory CLEMENT <gregory.clement@bootlin.com>  

Signed-off-by: Gabriel Matni <gabriel.matni@exfo.com> 


---
 drivers/tty/serial/mvebu-uart.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

-- 
2.7.4


> -----Original Message-----

> From: Miquel Raynal <miquel.raynal@bootlin.com>

> Sent: March 15, 2018 4:22 PM

> To: Gabriel Matni <gabriel.matni@exfo.com>

> Cc: gregkh@linuxfoundation.org; linux-serial@vger.kernel.org; linux-arm-

> kernel@lists.infradead.org; stable@vger.kernel.org; Grégory Clement

> <gregory.clement@bootlin.com>; Thomas Petazzoni

> <thomas.petazzoni@bootlin.com>

> Subject: Re: [PATCH] serial: mvebu-uart: fix tx lost characters

> 

> Hi Gabriel,

> 

> On Thu, 15 Mar 2018 18:55:25 +0000, Gabriel Matni

> <gabriel.matni@exfo.com> wrote:

> 

> > From: Gabriel Matni <gabriel.matni@exfo.com>

> >

> > Fixes missing characters on kernel console at low baud rates (i.e.9600).

> > The driver should poll TX_RDY or TX_FIFO_EMP instead of TX_EMP to

> ensure

> > that the transmitter holding register (THR) is ready to receive a new byte.

> >

> > TX_EMP tells us when it is possible to send a break sequence via

> > SND_BRK_SEQ. While this also indicates that both the THR and the TSR are

> > empty, it does not guarantee that a new byte can be written just yet.

> >

> > Fixes: 30530791a7a0 ("serial: mvebu-uart: initial support for Armada-3700

> >       serial port")

> > Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>

> > Acked-by: Gregory CLEMENT <gregory.clement@bootlin.com>

> > Signed-off-by: Gabriel Matni <gabriel.matni@exfo.com>

> >

> > ---

> >  drivers/tty/serial/mvebu-uart.c | 2 +-

> >  1 file changed, 1 insertion(+), 1 deletion(-)

> >

> > diff --git a/drivers/tty/serial/mvebu-uart.c b/drivers/tty/serial/mvebu-

> uart.c

> > index a100e98259d7..400e1bc558b2 100644

> > --- a/drivers/tty/serial/mvebu-uart.c

> > +++ b/drivers/tty/serial/mvebu-uart.c

> > @@ -618,7 +618,7 @@ static void wait_for_xmitr(struct uart_port *port)

> >  	u32 val;

> >

> >  	readl_poll_timeout_atomic(port->membase + UART_STAT, val,

> > -				  (val & STAT_TX_EMP), 1, 10000);

> > +             (val & STAT_TX_RDY(port)), 1, 10000);

> 

> I think this line should be indented like the one you replaced.

> 

> Thanks,

> Miquèl

> 

> --

> Miquel Raynal, Bootlin (formerly Free Electrons)

> Embedded Linux and Kernel engineering

> https://bootlin.com
diff mbox series

Patch

diff --git a/drivers/tty/serial/mvebu-uart.c b/drivers/tty/serial/mvebu-uart.c
index a100e98259d7..f0df0640208e 100644
--- a/drivers/tty/serial/mvebu-uart.c
+++ b/drivers/tty/serial/mvebu-uart.c
@@ -618,7 +618,7 @@  static void wait_for_xmitr(struct uart_port *port)
 	u32 val;
 
 	readl_poll_timeout_atomic(port->membase + UART_STAT, val,
-				  (val & STAT_TX_EMP), 1, 10000);
+				  (val & STAT_TX_RDY(port)), 1, 10000);
 }
 
 static void mvebu_uart_console_putchar(struct uart_port *port, int ch)