Linux Serial subsystem development

* RE: [PATCH v3] serial: mvebu-uart: fix tx lost characters
From: Gabriel Matni @ 2018-03-20 16:09 UTC (permalink / raw)
  To: gregkh@linuxfoundation.org
  Cc: Miquel Raynal, linux-serial@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, stable@vger.kernel.org,
	Grégory Clement, Thomas Petazzoni

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> 
---
Changes since v2:
- use one line for the "Fixes" entry
- removed trailing space between Signed-off-by entry and ---
- start using versioning, previous fixes in v1

Changes since v1:
- patch was corrupt, could not be applied
- fixed line indent
---
 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..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)
-- 
2.7.4


> -----Original Message-----
> From: gregkh@linuxfoundation.org <gregkh@linuxfoundation.org>
> Sent: March 20, 2018 5:32 AM
> To: Gabriel Matni <gabriel.matni@exfo.com>
> Cc: Miquel Raynal <miquel.raynal@bootlin.com>; 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
> 
> On Fri, Mar 16, 2018 at 01:45:32PM +0000, Gabriel Matni 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")
> 
> Can all be on one line.
> 
> And should this go to the stable trees?
> 
> > 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>
> 
> Trailing whitespace?
> 
> >
> > ---
> >  drivers/tty/serial/mvebu-uart.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> What version of this patch is this?  How do I know which to accept?
> 
> Please properly version your patch, and include the changes below the
> --- line like the documentation says to do.
> 
> thanks,
> 
> greg k-h

^ permalink raw reply related