[PATCH] serial/amba-pl011: fix minor bugs for pio mode

[PATCH] serial/amba-pl011: fix minor bugs for pio mode

[Leo Yan]

When use pio mode, there have two issues can be observed:

- In the commit 2240197 "serial/amba-pl011: Leave the TX IRQ alone when
  the UART is not open", it will skip clearing the TX IRQ across
  pl011_shutdown() and pl011_startup(); So at the next time after the
  uart port has been opened, there have chance for the function
  pl011_tx_chars() will not be executed if the TX IRQ will not be
  triggered; finally the console cannot output anymore.

  This is caused by the uart FIFO still keep data rather than
  the threshold. So revert this patch to make sure every time open the
  uart port, it will force to call function pl011_tx_chars().

- Sometimes will output the duplicate chars. Function pl011_tx_char()
  will firstly send char and check if FIFO is full, and if the FIFO is
  full it will return false; Caller function will consider the char
  has _NOT_ been send out and resend it again, finally will send the
  duplicate chars. So change to check FIFO is full or not, if full then
  return false, otherwise send out char and return true.

Signed-off-by: Leo Yan <leo.yan@linaro.org>
---
 drivers/tty/serial/amba-pl011.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 5a4e9d5..9d9ac76 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -1249,20 +1249,19 @@ __acquires(&uap->port.lock)
 
 /*
  * Transmit a character
- * There must be at least one free entry in the TX FIFO to accept the char.
  *
- * Returns true if the FIFO might have space in it afterwards;
- * returns false if the FIFO definitely became full.
+ * Before send character, need check FIFO is full or not;
+ * If FIFO is full, will not send char and return false,
+ * otherwise send out character and return ture.
  */
 static bool pl011_tx_char(struct uart_amba_port *uap, unsigned char c)
 {
+	if (readw(uap->port.membase + UART01x_FR) & UART01x_FR_TXFF)
+		return false;
+
 	writew(c, uap->port.membase + UART01x_DR);
 	uap->port.icount.tx++;
-
-	if (likely(uap->tx_irq_seen > 1))
-		return true;
-
-	return !(readw(uap->port.membase + UART01x_FR) & UART01x_FR_TXFF);
+	return true;
 }
 
 static bool pl011_tx_chars(struct uart_amba_port *uap)
@@ -1639,6 +1638,9 @@ static int pl011_startup(struct uart_port *port)
 
 	writew(uap->vendor->ifls, uap->port.membase + UART011_IFLS);
 
+	/* Assume that TX IRQ doesn't work until we see one: */
+	uap->tx_irq_seen = 0;
+
 	spin_lock_irq(&uap->port.lock);
 
 	/* restore RTS and DTR */
@@ -1702,7 +1704,7 @@ static void pl011_shutdown(struct uart_port *port)
 	spin_lock_irq(&uap->port.lock);
 	uap->im = 0;
 	writew(uap->im, uap->port.membase + UART011_IMSC);
-	writew(0xffff & ~UART011_TXIS, uap->port.membase + UART011_ICR);
+	writew(0xffff, uap->port.membase + UART011_ICR);
 	spin_unlock_irq(&uap->port.lock);
 
 	pl011_dma_shutdown(uap);
-- 
1.9.1

Re: [PATCH] serial/amba-pl011: fix minor bugs for pio mode

[Daniel Thompson]

On 05/05/15 04:00, Leo Yan wrote:
> When use pio mode, there have two issues can be observed:
>
> - In the commit 2240197 "serial/amba-pl011: Leave the TX IRQ alone when
>    the UART is not open", it will skip clearing the TX IRQ across
>    pl011_shutdown() and pl011_startup(); So at the next time after the
>    uart port has been opened, there have chance for the function
>    pl011_tx_chars() will not be executed if the TX IRQ will not be
>    triggered; finally the console cannot output anymore.
>
>    This is caused by the uart FIFO still keep data rather than
>    the threshold. So revert this patch to make sure every time open the
>    uart port, it will force to call function pl011_tx_chars().
>
> - Sometimes will output the duplicate chars. Function pl011_tx_char()
>    will firstly send char and check if FIFO is full, and if the FIFO is
>    full it will return false; Caller function will consider the char
>    has _NOT_ been send out and resend it again, finally will send the
>    duplicate chars. So change to check FIFO is full or not, if full then
>    return false, otherwise send out char and return true.

I was going to comment that this patch should probably be split into two 
patches...

However whilst doing background reading I noticed that for both these 
issues there are existing patches to address them:

http://lists.infradead.org/pipermail/linux-arm-kernel/2015-March/334107.html

Do these fix the issues for you?


>
> Signed-off-by: Leo Yan <leo.yan@linaro.org>
> ---
>   drivers/tty/serial/amba-pl011.c | 20 +++++++++++---------
>   1 file changed, 11 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
> index 5a4e9d5..9d9ac76 100644
> --- a/drivers/tty/serial/amba-pl011.c
> +++ b/drivers/tty/serial/amba-pl011.c
> @@ -1249,20 +1249,19 @@ __acquires(&uap->port.lock)
>
>   /*
>    * Transmit a character
> - * There must be at least one free entry in the TX FIFO to accept the char.
>    *
> - * Returns true if the FIFO might have space in it afterwards;
> - * returns false if the FIFO definitely became full.
> + * Before send character, need check FIFO is full or not;
> + * If FIFO is full, will not send char and return false,
> + * otherwise send out character and return ture.
>    */
>   static bool pl011_tx_char(struct uart_amba_port *uap, unsigned char c)
>   {
> +	if (readw(uap->port.membase + UART01x_FR) & UART01x_FR_TXFF)
> +		return false;
> +
>   	writew(c, uap->port.membase + UART01x_DR);
>   	uap->port.icount.tx++;
> -
> -	if (likely(uap->tx_irq_seen > 1))
> -		return true;
> -
> -	return !(readw(uap->port.membase + UART01x_FR) & UART01x_FR_TXFF);
> +	return true;
>   }
>
>   static bool pl011_tx_chars(struct uart_amba_port *uap)
> @@ -1639,6 +1638,9 @@ static int pl011_startup(struct uart_port *port)
>
>   	writew(uap->vendor->ifls, uap->port.membase + UART011_IFLS);
>
> +	/* Assume that TX IRQ doesn't work until we see one: */
> +	uap->tx_irq_seen = 0;
> +
>   	spin_lock_irq(&uap->port.lock);
>
>   	/* restore RTS and DTR */
> @@ -1702,7 +1704,7 @@ static void pl011_shutdown(struct uart_port *port)
>   	spin_lock_irq(&uap->port.lock);
>   	uap->im = 0;
>   	writew(uap->im, uap->port.membase + UART011_IMSC);
> -	writew(0xffff & ~UART011_TXIS, uap->port.membase + UART011_ICR);
> +	writew(0xffff, uap->port.membase + UART011_ICR);
>   	spin_unlock_irq(&uap->port.lock);
>
>   	pl011_dma_shutdown(uap);
>

Re: [PATCH] serial/amba-pl011: fix minor bugs for pio mode

[Dave P Martin]

Hi,

On Tue, May 05, 2015 at 04:00:25AM +0100, Leo Yan wrote:
> When use pio mode, there have two issues can be observed:
> 
> - In the commit 2240197 "serial/amba-pl011: Leave the TX IRQ alone when
>   the UART is not open", it will skip clearing the TX IRQ across
>   pl011_shutdown() and pl011_startup(); So at the next time after the
>   uart port has been opened, there have chance for the function
>   pl011_tx_chars() will not be executed if the TX IRQ will not be
>   triggered; finally the console cannot output anymore.
> 
>   This is caused by the uart FIFO still keep data rather than
>   the threshold. So revert this patch to make sure every time open the
>   uart port, it will force to call function pl011_tx_chars().
> 
> - Sometimes will output the duplicate chars. Function pl011_tx_char()
>   will firstly send char and check if FIFO is full, and if the FIFO is
>   full it will return false; Caller function will consider the char
>   has _NOT_ been send out and resend it again, finally will send the
>   duplicate chars. So change to check FIFO is full or not, if full then
>   return false, otherwise send out char and return true.
> 
> Signed-off-by: Leo Yan <leo.yan@linaro.org>

[...]

Thanks for the fixes, but I already posted patches that probably fix the
issues you are observing, And Greg took them into his tty-testing branch.

Can you give them a try instead of your patches?

Dave Martin (2):
      Revert "serial/amba-pl011: Leave the TX IRQ alone when the UART is not open"
      serial/amba-pl011: Refactor and simplify TX FIFO handling

from

git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git tty-testing


It would be good to have some feedback on them.

Cheers
---Dave

Re: [PATCH] serial/amba-pl011: fix minor bugs for pio mode

[Leo Yan]

On Tue, May 05, 2015 at 12:11:56PM +0100, Dave P Martin wrote:
> On Tue, May 05, 2015 at 04:00:25AM +0100, Leo Yan wrote:
> [...]
> 
> Thanks for the fixes, but I already posted patches that probably fix the
> issues you are observing, And Greg took them into his tty-testing branch.
> 
> Can you give them a try instead of your patches?
> 
> Dave Martin (2):
>       Revert "serial/amba-pl011: Leave the TX IRQ alone when the UART is not open"
>       serial/amba-pl011: Refactor and simplify TX FIFO handling
> 
> from
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git tty-testing
> 
> 
> It would be good to have some feedback on them.

Tested w/t your two patches, it can fix issues quite well;
Also will back port them into local branch. Thanks u and Daniel
pointing out this.

Tested-by: Leo Yan <leo.yan@linaro.com>

Thanks,
Leo Yan

Re: [PATCH] serial/amba-pl011: fix minor bugs for pio mode

[Leo Yan]

On Tue, May 05, 2015 at 08:09:27PM +0800, Leo Yan wrote:
> On Tue, May 05, 2015 at 12:11:56PM +0100, Dave P Martin wrote:
> > On Tue, May 05, 2015 at 04:00:25AM +0100, Leo Yan wrote:
> > [...]
> > 
> > Thanks for the fixes, but I already posted patches that probably fix the
> > issues you are observing, And Greg took them into his tty-testing branch.
> > 
> > Can you give them a try instead of your patches?
> > 
> > Dave Martin (2):
> >       Revert "serial/amba-pl011: Leave the TX IRQ alone when the UART is not open"
> >       serial/amba-pl011: Refactor and simplify TX FIFO handling
> > 
> > from
> > 
> > git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git tty-testing
> > 
> > 
> > It would be good to have some feedback on them.
> 
> Tested w/t your two patches, it can fix issues quite well;
> Also will back port them into local branch. Thanks u and Daniel
> pointing out this.

Sorry, fix typo:

Tested-by: Leo Yan <leo.yan@linaro.org>

> Thanks,
> Leo Yan

Re: [PATCH] serial/amba-pl011: fix minor bugs for pio mode

[Dave Martin]

On Tue, May 05, 2015 at 08:11:12PM +0800, Leo Yan wrote:
> On Tue, May 05, 2015 at 08:09:27PM +0800, Leo Yan wrote:
> > On Tue, May 05, 2015 at 12:11:56PM +0100, Dave P Martin wrote:
> > > On Tue, May 05, 2015 at 04:00:25AM +0100, Leo Yan wrote:
> > > [...]
> > > 
> > > Thanks for the fixes, but I already posted patches that probably fix the
> > > issues you are observing, And Greg took them into his tty-testing branch.
> > > 
> > > Can you give them a try instead of your patches?
> > > 
> > > Dave Martin (2):
> > >       Revert "serial/amba-pl011: Leave the TX IRQ alone when the UART is not open"
> > >       serial/amba-pl011: Refactor and simplify TX FIFO handling
> > > 
> > > from
> > > 
> > > git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git tty-testing
> > > 
> > > 
> > > It would be good to have some feedback on them.
> > 
> > Tested w/t your two patches, it can fix issues quite well;
> > Also will back port them into local branch. Thanks u and Daniel
> > pointing out this.
> 
> Sorry, fix typo:
> 
> Tested-by: Leo Yan <leo.yan@linaro.org>

Thanks
---Dave