serial: mvebu-uart: fix tx lost characters

PATCH New Gabriel Matni 3 participants 6 messages Mar 6, 2018 – Mar 20, 2018

Subsystems (3)

Stable branch TTY layer and serial drivers Marvell armada 3700 serial driver

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Gabriel Matni

author

2018-03-06 15:47 UTC #0 lore raw

PATCH 1/1 serial: mvebu-uart: fix tx lost characters

From: Gabriel Matni <[email protected]>

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 <[email protected]>

Acked-by Gregory CLEMENT <[email protected]>

Signed-off-by Gabriel Matni <[email protected]>

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

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

drivers/tty/serial/mvebu-uart.c +1 -1

index a100e98259d7..f0df0640208e 100644
@@ -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

Quoted 99 lines

-----Original Message-----
From: Miquel Raynal [mailto:miquel.raynal at bootlin.com]
Sent: March 5, 2018 4:47 AM
To: Gabriel Matni <[email protected]>
Cc: linux-arm-kernel at lists.infradead.org; gregkh at linuxfoundation.org; Gr?gory Clement <[email protected]>; Thomas Petazzoni <[email protected]>
Subject: Re: [PATCH] serial: mvebu_uart: fix tx lost characters
Hi Gabriel,
Quoted 22 lines · Gabriel Matni
Hi Miqu?l,
Quoted 20 lines
-----Original Message-----
From: Miquel Raynal [mailto:miquel.raynal at bootlin.com]
Sent: February 27, 2018 8:13 AM
To: Gabriel Matni <[email protected]>
Cc: linux-arm-kernel at lists.infradead.org; gregkh at linuxfoundation.org; Gr?gory Clement <[email protected]>; Thomas Petazzoni <[email protected]>
Subject: Re: [PATCH] serial: mvebu_uart: fix tx lost characters
Hi Gabriel,
Quoted 6 lines · Gabriel Matni
From: Gabriel Matni <[email protected]>
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
Quoted 4 lines
Quoted 4 lines
Quoted 1 line
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.
Quoted 3 lines
Quoted 3 lines
- 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
Quoted 1 line
Quoted 1 line
would fix the loss of character by filling the FIFO when there are bytes in
it
Quoted 3 lines
Quoted 1 line
rather than when it is fully empty.
TX_READY is set whenever the UART Transmitter Holding register is ready
to
Quoted 6 lines
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.
Quoted 2 lines
I am
unsure about the FIFO status in this case as I can encounter
TX_FIFO_EMP=0
Quoted 1 line
while TX_EMP=1, which suggests that the FIFO isn't necessarily empty
when
Quoted 1 line
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.
Quoted 4 lines
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.
Quoted 3 lines
Quoted 3 lines
Quoted 3 lines
Signed-off-by Gabriel Matni <[email protected]>
Reviewed-by Miquel Raynal <[email protected]>
Thanks,
Miqu?l
--
Miquel Raynal, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com

gregkh at linuxfoundation.org

maintainer

2018-03-15 16:55 UTC #1 lore raw

PATCH 1/1 serial: mvebu-uart: fix tx lost characters

Quoted 32 lines · Gabriel Matni

From: Gabriel Matni <[email protected]>
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 <[email protected]>
Acked-by Gregory CLEMENT <[email protected]>
Signed-off-by Gabriel Matni <[email protected]>
---
drivers/tty/serial/mvebu-uart.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
drivers/tty/serial/mvebu-uart.c +1 -2
index a100e98259d7..f0df0640208e 100644
@@ -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)
--

Quoted 1 line

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

Gabriel Matni

author

2018-03-15 18:55 UTC #2 lore raw

PATCH 1/1 serial: mvebu-uart: fix tx lost characters

From: Gabriel Matni <[email protected]>

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

serial port")

Reviewed-by Miquel Raynal <[email protected]>

Acked-by Gregory CLEMENT <[email protected]>

Signed-off-by Gabriel Matni <[email protected]>

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

drivers/tty/serial/mvebu-uart.c +1 -1

index a100e98259d7..400e1bc558b2 100644
@@ -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)

Signature · 1 line

2.7.4

Quoted 58 lines

-----Original Message-----
From: gregkh at linuxfoundation.org <[email protected]>
Sent: March 15, 2018 12:55 PM
To: Gabriel Matni <[email protected]>
Cc: linux-arm-kernel at lists.infradead.org; stable at vger.kernel.org; Miquel Raynal <[email protected]>; Gr?gory Clement <[email protected]>; Thomas Petazzoni <[email protected]>
Subject: Re: [PATCH] serial: mvebu-uart: fix tx lost characters
Quoted 4 lines · Gabriel Matni
From: Gabriel Matni <[email protected]>
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
Quoted 7 lines
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")
drivers/tty/serial/mvebu-
Quoted 8 lines
Reviewed-by Miquel Raynal <[email protected]>
Acked-by Gregory CLEMENT <[email protected]>
Signed-off-by Gabriel Matni <[email protected]>
---
drivers/tty/serial/mvebu-uart.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
drivers/tty/serial/mvebu- renamed from drivers/tty/serial/mvebu-uart.c +0 -0
uart.c
Quoted 13 lines
index a100e98259d7..f0df0640208e 100644
drivers/tty/serial/mvebu-uart.c +1 -2
@@ -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)
--
Quoted 1 line
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

Miquel Raynal

2018-03-15 20:21 UTC #3 lore raw

PATCH 1/1 serial: mvebu-uart: fix tx lost characters

Hi Gabriel,

Quoted 25 lines · Gabriel Matni

From: Gabriel Matni <[email protected]>
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 <[email protected]>
Acked-by Gregory CLEMENT <[email protected]>
Signed-off-by Gabriel Matni <[email protected]>
---
 drivers/tty/serial/mvebu-uart.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
drivers/tty/serial/mvebu-uart.c +0 -0
index a100e98259d7..400e1bc558b2 100644

drivers/tty/serial/mvebu-uart.c static void wait_for_xmitr(struct uart_port *port) · line 621

Quoted 5 lines

drivers/tty/serial/mvebu-uart.c +1 -1

@@ -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,
Miqu?l

Signature · 3 lines

Miquel Raynal, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com

Gabriel Matni

author

2018-03-16 13:45 UTC #4 lore raw

PATCH 1/1 serial: mvebu-uart: fix tx lost characters

From: Gabriel Matni <[email protected]>

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

serial port")

Reviewed-by Miquel Raynal <[email protected]>

Acked-by Gregory CLEMENT <[email protected]>

Signed-off-by Gabriel Matni <[email protected]>

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

drivers/tty/serial/mvebu-uart.c +1 -1

index a100e98259d7..f0df0640208e 100644
@@ -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)

Signature · 1 line

2.7.4

Quoted 57 lines

-----Original Message-----
From: Miquel Raynal <[email protected]>
Sent: March 15, 2018 4:22 PM
To: Gabriel Matni <[email protected]>
Cc: gregkh at linuxfoundation.org; linux-serial at vger.kernel.org; linux-arm- kernel at lists.infradead.org; stable at vger.kernel.org; Gr?gory Clement <[email protected]>; Thomas Petazzoni <[email protected]>
Subject: Re: [PATCH] serial: mvebu-uart: fix tx lost characters
Hi Gabriel,
Quoted 4 lines · Gabriel Matni
From: Gabriel Matni <[email protected]>
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
drivers/tty/serial/mvebu-
Quoted 17 lines
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 <[email protected]>
Acked-by Gregory CLEMENT <[email protected]>
Signed-off-by Gabriel Matni <[email protected]>
---
 drivers/tty/serial/mvebu-uart.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
drivers/tty/serial/mvebu- renamed from drivers/tty/serial/mvebu-uart.c +0 -0
uart.c
drivers/tty/serial/mvebu-uart.c static void wait_for_xmitr(struct uart_port *port) · line 621
Quoted 9 lines
index a100e98259d7..400e1bc558b2 100644
drivers/tty/serial/mvebu-uart.c +1 -1
@@ -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,
Miqu?l
--
Miquel Raynal, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com

gregkh at linuxfoundation.org

maintainer

2018-03-20 09:32 UTC #5 lore raw

PATCH 1/1 serial: mvebu-uart: fix tx lost characters

Quoted 6 lines · Gabriel Matni

From: Gabriel Matni <[email protected]>
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.

Quoted 6 lines

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?

Quoted 3 lines

Reviewed-by Miquel Raynal <[email protected]>
Acked-by Gregory CLEMENT <[email protected]>
Signed-off-by Gabriel Matni <[email protected]>

Trailing whitespace?

Quoted 4 lines

---
 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