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..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: Miquel Raynal [mailto:miquel.raynal@bootlin.com] Sent: March 5, 2018 4:47 AM To: Gabriel Matni gabriel.matni@exfo.com Cc: linux-arm-kernel@lists.infradead.org; gregkh@linuxfoundation.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 Tue, 27 Feb 2018 21:56:03 +0000, Gabriel Matni gabriel.matni@exfo.com wrote:
Hi Miquèl,
-----Original Message----- From: Miquel Raynal [mailto:miquel.raynal@bootlin.com] Sent: February 27, 2018 8:13 AM To: Gabriel Matni gabriel.matni@exfo.com Cc: linux-arm-kernel@lists.infradead.org; gregkh@linuxfoundation.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, 22 Feb 2018 20:30:56 +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 instead of TX_EMPTY to ensure that the transmitter holding is ready to receive a new byte. Polling TX_EMPTY isn't enough as the hardware buffer can become empty but not yet
ready
for CPU to write the next byte.
I am kind of sceptic with the explanation. My understanding is that:
- TX_EMPTY means the FIFO is empty
I had a deeper look into the spec : TX_EMPTY != TX_FIFO_EMPTY. I was referring to TX_FIFO_EMPTY here so my understanding of your solution was wrong.
- TX_RDY means the FIFO is not full, neither empty, it is a "half loaded" state.
Polling TX_RDY instead of TX_EMPTY should work too, but I don't see why
it
would fix the loss of character by filling the FIFO when there are bytes in
it
rather than when it is fully empty.
TX_READY is set whenever the UART Transmitter Holding register is ready
to
receive a new byte. It gets cleared as soon as a new byte is written to the register. If the FIFO is empty or still has room, the ready will be set.
TX_EMPTY 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.
I do agree with this statement. You are right that polling on TX_EMPTY looks wrong and we should definitively poll on TX_READY instead.
I am unsure about the FIFO status in this case as I can encounter
TX_FIFO_EMP=0
while TX_EMP=1, which suggests that the FIFO isn't necessarily empty
when
TX_EMP is set.
That is weird but maybe the TX_FIFO_EMPTY is asserted only when all bits have been shifted, which is a 10-bit period after TSR is cleared, while TX_EMPTY would not wait for these bits to be actually shifted out and would be asserted a bit earlier, as soon as TSR is cleared. That is just and idea.
Therefore, the driver can either poll TX_FIFO_EMP or TX_READY to know whether it can output a new byte. I personally like TX_READY as it takes advantage of the FIFO.
True.
Signed-off-by: Gabriel Matni gabriel.matni@exfo.com
Reviewed-by: Miquel Raynal miquel.raynal@bootlin.com
Thanks, Miquèl
-- Miquel Raynal, Bootlin (formerly Free Electrons) Embedded Linux and Kernel engineering https://bootlin.com
On Tue, Mar 06, 2018 at 03:47:03PM +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") 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..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
Patch is corrupted and can not be applied :(
Please fix up and resend.
Also be sure to cc: the linux-serial mailing list, scripts/get_maintainer.pl is your friend...
thanks,
greg k-h
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); }
static void mvebu_uart_console_putchar(struct uart_port *port, int ch)
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
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..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)
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
linux-stable-mirror@lists.linaro.org
-
Gabriel Matni -
gregkh＠linuxfoundation.org -
Miquel Raynal