[RFC PATCHv2 0/4] omap-serial high-speed fixes/improvements

[RFC PATCHv2 0/4] omap-serial high-speed fixes/improvements

[Frans Klaver]

Here's version 2 of the patches that should improve the behavior of the omap
serial port at high baud and data rates.

Differences with regard to v1 are:
  - centralize baud_is_mode16's calculation
  - fix/unbreak an uninitialized variable in "use threaded interrupt handler"
  - read has-hw-flow-control property in of_get_uart_port_info

Frans Klaver (4):
  tty: omap-serial: pull out calculation from baud_is_mode16
  tty: omap-serial: prevent division by zero
  tty: omap-serial: use threaded interrupt handler
  tty: omap-serial: support setting of hardware flow control in dts

 .../devicetree/bindings/serial/omap_serial.txt     |  1 +
 drivers/tty/serial/omap-serial.c                   | 65 +++++++++++++++++-----
 2 files changed, 51 insertions(+), 15 deletions(-)

-- 
1.9.3

[PATCH 1/4] tty: omap-serial: pull out calculation from baud_is_mode16

[Frans Klaver]

To determine the correct divisor, we need to know the difference between
the desired baud rate and the actual baud rate. The calculation for this
difference is implemented twice within omap_serial_baud_is_mode16().
Pull out the calculation for easier maintenance.

Signed-off-by: Frans Klaver <frans.klaver@xsens.com>
---
 drivers/tty/serial/omap-serial.c | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
index d017cec..ae935ce 100644
--- a/drivers/tty/serial/omap-serial.c
+++ b/drivers/tty/serial/omap-serial.c
@@ -239,6 +239,22 @@ static void serial_omap_enable_wakeup(struct uart_omap_port *up, bool enable)
 }
 
 /*
+ * Calculate the absolute difference between the desired and actual baud
+ * rate for the given mode.
+ */
+static inline int calculate_baud_abs_diff(struct uart_port *port,
+				unsigned int baud, unsigned int mode)
+{
+	unsigned int n = port->uartclk / (mode * baud);
+	int abs_diff = baud - (port->uartclk / (mode * n));
+
+	if (abs_diff < 0)
+		abs_diff = -abs_diff;
+
+	return abs_diff;
+}
+
+/*
  * serial_omap_baud_is_mode16 - check if baud rate is MODE16X
  * @port: uart port info
  * @baud: baudrate for which mode needs to be determined
@@ -252,14 +268,8 @@ static void serial_omap_enable_wakeup(struct uart_omap_port *up, bool enable)
 static bool
 serial_omap_baud_is_mode16(struct uart_port *port, unsigned int baud)
 {
-	unsigned int n13 = port->uartclk / (13 * baud);
-	unsigned int n16 = port->uartclk / (16 * baud);
-	int baudAbsDiff13 = baud - (port->uartclk / (13 * n13));
-	int baudAbsDiff16 = baud - (port->uartclk / (16 * n16));
-	if (baudAbsDiff13 < 0)
-		baudAbsDiff13 = -baudAbsDiff13;
-	if (baudAbsDiff16 < 0)
-		baudAbsDiff16 = -baudAbsDiff16;
+	int baudAbsDiff13 = calculate_baud_abs_diff(port, baud, 13);
+	int baudAbsDiff16 = calculate_baud_abs_diff(port, baud, 16);
 
 	return (baudAbsDiff13 >= baudAbsDiff16);
 }
-- 
1.9.3

[PATCH 2/4] tty: omap-serial: prevent division by zero

[Frans Klaver]

If the chosen baud rate is large enough (e.g. 3.5 megabaud), the
calculated n values in calculate_baud_abs_diff may become 0. This causes
a division by zero when calculating the difference between calculated
and desired baud rates. To prevent this, cap n on 1.

Signed-off-by: Frans Klaver <frans.klaver@xsens.com>
---
 drivers/tty/serial/omap-serial.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
index ae935ce..14a0167 100644
--- a/drivers/tty/serial/omap-serial.c
+++ b/drivers/tty/serial/omap-serial.c
@@ -246,8 +246,12 @@ static inline int calculate_baud_abs_diff(struct uart_port *port,
 				unsigned int baud, unsigned int mode)
 {
 	unsigned int n = port->uartclk / (mode * baud);
-	int abs_diff = baud - (port->uartclk / (mode * n));
+	int abs_diff;
 
+	if (n == 0)
+		n = 1;
+
+	abs_diff = baud - (uartclk / (mode * n));
 	if (abs_diff < 0)
 		abs_diff = -abs_diff;
 
-- 
1.9.3

[RFC PATCH 3/4] tty: omap-serial: use threaded interrupt handler

[Frans Klaver]

At 3.6Mbaud, with slightly over 2Mbit/s data coming in, we see 1600 uart
rx buffer overflows within 30 seconds. Threading the interrupt handling reduces
this to about 170 overflows in 10 minutes.

In practice this therefore reduces the need for hardware flow control,
meaning the sending side doesn't have to buffer as much either.

Signed-off-by: Frans Klaver <frans.klaver@xsens.com>
---
 drivers/tty/serial/omap-serial.c | 31 ++++++++++++++++++++++++-------
 1 file changed, 24 insertions(+), 7 deletions(-)

diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
index 14a0167..57664b9 100644
--- a/drivers/tty/serial/omap-serial.c
+++ b/drivers/tty/serial/omap-serial.c
@@ -575,6 +575,21 @@ static void serial_omap_rdi(struct uart_omap_port *up, unsigned int lsr)
 }
 
 /**
+ * serial_omap_fast_irq() - schedule interrupt handling
+ */
+static irqreturn_t serial_omap_fast_irq(int irq, void *dev_id)
+{
+	struct uart_omap_port *up = dev_id;
+	unsigned int iir = serial_in(up, UART_IIR);
+
+	if (iir & UART_IIR_NO_INT)
+		return IRQ_NONE;
+
+	disable_irq_nosync(up->port.irq);
+	return IRQ_WAKE_THREAD;
+}
+
+/**
  * serial_omap_irq() - This handles the interrupt from one port
  * @irq: uart port irq number
  * @dev_id: uart port info
@@ -584,7 +599,6 @@ static irqreturn_t serial_omap_irq(int irq, void *dev_id)
 	struct uart_omap_port *up = dev_id;
 	unsigned int iir, lsr;
 	unsigned int type;
-	irqreturn_t ret = IRQ_NONE;
 	int max_count = 256;
 
 	spin_lock(&up->port.lock);
@@ -595,7 +609,6 @@ static irqreturn_t serial_omap_irq(int irq, void *dev_id)
 		if (iir & UART_IIR_NO_INT)
 			break;
 
-		ret = IRQ_HANDLED;
 		lsr = serial_in(up, UART_LSR);
 
 		/* extract IRQ type from IIR register */
@@ -630,11 +643,13 @@ static irqreturn_t serial_omap_irq(int irq, void *dev_id)
 
 	tty_flip_buffer_push(&up->port.state->port);
 
+	enable_irq(up->port.irq);
+
 	pm_runtime_mark_last_busy(up->dev);
 	pm_runtime_put_autosuspend(up->dev);
 	up->port_activity = jiffies;
 
-	return ret;
+	return IRQ_HANDLED;
 }
 
 static unsigned int serial_omap_tx_empty(struct uart_port *port)
@@ -731,15 +746,17 @@ static int serial_omap_startup(struct uart_port *port)
 	/*
 	 * Allocate the IRQ
 	 */
-	retval = request_irq(up->port.irq, serial_omap_irq, up->port.irqflags,
-				up->name, up);
+	retval = request_threaded_irq(up->port.irq, serial_omap_fast_irq,
+					serial_omap_irq, up->port.irqflags,
+					up->name, up);
 	if (retval)
 		return retval;
 
 	/* Optional wake-up IRQ */
 	if (up->wakeirq) {
-		retval = request_irq(up->wakeirq, serial_omap_irq,
-				     up->port.irqflags, up->name, up);
+		retval = request_threaded_irq(up->wakeirq, serial_omap_fast_irq,
+					serial_omap_irq, up->port.irqflags,
+					up->name, up);
 		if (retval) {
 			free_irq(up->port.irq, up);
 			return retval;
-- 
1.9.3

[RFC PATCH 3/4] tty: omap-serial: use threaded interrupt handler

[Felipe Balbi]

On Tue, Aug 19, 2014 at 02:14:47PM +0200, Frans Klaver wrote:
> At 3.6Mbaud, with slightly over 2Mbit/s data coming in, we see 1600 uart
> rx buffer overflows within 30 seconds. Threading the interrupt handling reduces
> this to about 170 overflows in 10 minutes.

Can you try Sebastian Siewior's patches for 8250_omap and 8250 dma
support ? That should help you a lot.

> In practice this therefore reduces the need for hardware flow control,
> meaning the sending side doesn't have to buffer as much either.
> 
> Signed-off-by: Frans Klaver <frans.klaver@xsens.com>
> ---
>  drivers/tty/serial/omap-serial.c | 31 ++++++++++++++++++++++++-------
>  1 file changed, 24 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
> index 14a0167..57664b9 100644
> --- a/drivers/tty/serial/omap-serial.c
> +++ b/drivers/tty/serial/omap-serial.c
> @@ -575,6 +575,21 @@ static void serial_omap_rdi(struct uart_omap_port *up, unsigned int lsr)
>  }
>  
>  /**
> + * serial_omap_fast_irq() - schedule interrupt handling
> + */
> +static irqreturn_t serial_omap_fast_irq(int irq, void *dev_id)
> +{
> +	struct uart_omap_port *up = dev_id;
> +	unsigned int iir = serial_in(up, UART_IIR);
> +
> +	if (iir & UART_IIR_NO_INT)
> +		return IRQ_NONE;
> +
> +	disable_irq_nosync(up->port.irq);

NAK. Either use IRQF_ONESHOT or actually mask the IRQs at the device's
registers (basically clearing IER).

-- 
balbi
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[RFC PATCH 3/4] tty: omap-serial: use threaded interrupt handler

[Frans Klaver]

On Tue, Aug 19, 2014 at 01:57:02PM -0500, Felipe Balbi wrote:
> On Tue, Aug 19, 2014 at 02:14:47PM +0200, Frans Klaver wrote:
> > At 3.6Mbaud, with slightly over 2Mbit/s data coming in, we see 1600 uart
> > rx buffer overflows within 30 seconds. Threading the interrupt handling reduces
> > this to about 170 overflows in 10 minutes.
> 
> Can you try Sebastian Siewior's patches for 8250_omap and 8250 dma
> support ? That should help you a lot.

I'll have a look at that series. Thanks for pointing it out.

> >  drivers/tty/serial/omap-serial.c | 31 ++++++++++++++++++++++++-------
> >  1 file changed, 24 insertions(+), 7 deletions(-)
> > 
> > diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
> > index 14a0167..57664b9 100644
> > --- a/drivers/tty/serial/omap-serial.c
> > +++ b/drivers/tty/serial/omap-serial.c
> > @@ -575,6 +575,21 @@ static void serial_omap_rdi(struct uart_omap_port *up, unsigned int lsr)
> >  }
> >  
> >  /**
> > + * serial_omap_fast_irq() - schedule interrupt handling
> > + */
> > +static irqreturn_t serial_omap_fast_irq(int irq, void *dev_id)
> > +{
> > +	struct uart_omap_port *up = dev_id;
> > +	unsigned int iir = serial_in(up, UART_IIR);
> > +
> > +	if (iir & UART_IIR_NO_INT)
> > +		return IRQ_NONE;
> > +
> > +	disable_irq_nosync(up->port.irq);
> 
> NAK. Either use IRQF_ONESHOT or actually mask the IRQs at the device's
> registers (basically clearing IER).

Given the work that's been done on the 8250 based driver, what are the
short-term chances omap-serial will be dropped? I'd be happy to improve
here if it makes sense to do so. If the 8250 based driver is going to
replace omap-serial anyway on the short term, I don't see the point of
further developing this patch. The others would still make sense in my
opinion.

Thanks,
Frans

[RFC PATCH 3/4] tty: omap-serial: use threaded interrupt handler

[Felipe Balbi]

On Wed, Aug 20, 2014 at 08:40:28AM +0200, Frans Klaver wrote:
> On Tue, Aug 19, 2014 at 01:57:02PM -0500, Felipe Balbi wrote:
> > On Tue, Aug 19, 2014 at 02:14:47PM +0200, Frans Klaver wrote:
> > > At 3.6Mbaud, with slightly over 2Mbit/s data coming in, we see 1600 uart
> > > rx buffer overflows within 30 seconds. Threading the interrupt handling reduces
> > > this to about 170 overflows in 10 minutes.
> > 
> > Can you try Sebastian Siewior's patches for 8250_omap and 8250 dma
> > support ? That should help you a lot.
> 
> I'll have a look at that series. Thanks for pointing it out.
> 
> > >  drivers/tty/serial/omap-serial.c | 31 ++++++++++++++++++++++++-------
> > >  1 file changed, 24 insertions(+), 7 deletions(-)
> > > 
> > > diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
> > > index 14a0167..57664b9 100644
> > > --- a/drivers/tty/serial/omap-serial.c
> > > +++ b/drivers/tty/serial/omap-serial.c
> > > @@ -575,6 +575,21 @@ static void serial_omap_rdi(struct uart_omap_port *up, unsigned int lsr)
> > >  }
> > >  
> > >  /**
> > > + * serial_omap_fast_irq() - schedule interrupt handling
> > > + */
> > > +static irqreturn_t serial_omap_fast_irq(int irq, void *dev_id)
> > > +{
> > > +	struct uart_omap_port *up = dev_id;
> > > +	unsigned int iir = serial_in(up, UART_IIR);
> > > +
> > > +	if (iir & UART_IIR_NO_INT)
> > > +		return IRQ_NONE;
> > > +
> > > +	disable_irq_nosync(up->port.irq);
> > 
> > NAK. Either use IRQF_ONESHOT or actually mask the IRQs at the device's
> > registers (basically clearing IER).
> 
> Given the work that's been done on the 8250 based driver, what are the
> short-term chances omap-serial will be dropped? I'd be happy to improve
> here if it makes sense to do so. If the 8250 based driver is going to
> replace omap-serial anyway on the short term, I don't see the point of
> further developing this patch. The others would still make sense in my
> opinion.

if we find a way to maintain the same ttyO* naming scheme and make it
coexist with ttyS* naming, then we could drop as soon as 8250_omap is
ready for prime time.

-- 
balbi
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[RFC PATCH 3/4] tty: omap-serial: use threaded interrupt handler

[Frans Klaver]

On Wed, Aug 20, 2014 at 11:06:05AM -0500, Felipe Balbi wrote:
> On Wed, Aug 20, 2014 at 08:40:28AM +0200, Frans Klaver wrote:
> > On Tue, Aug 19, 2014 at 01:57:02PM -0500, Felipe Balbi wrote:
> > > On Tue, Aug 19, 2014 at 02:14:47PM +0200, Frans Klaver wrote:
> > > > At 3.6Mbaud, with slightly over 2Mbit/s data coming in, we see 1600 uart
> > > > rx buffer overflows within 30 seconds. Threading the interrupt handling reduces
> > > > this to about 170 overflows in 10 minutes.
> > > 
> > > Can you try Sebastian Siewior's patches for 8250_omap and 8250 dma
> > > support ? That should help you a lot.
> > 
> > I'll have a look at that series. Thanks for pointing it out.

I have had a look at Sebastian's series, but I'm not convinced
yet that we should use it. So far the serial console seems to be
missing data every now and then. I haven't gotten around to testing our
high traffic application yet.


> > > >  drivers/tty/serial/omap-serial.c | 31 ++++++++++++++++++++++++-------
> > > >  1 file changed, 24 insertions(+), 7 deletions(-)
> > > > 
> > > > diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
> > > > index 14a0167..57664b9 100644
> > > > --- a/drivers/tty/serial/omap-serial.c
> > > > +++ b/drivers/tty/serial/omap-serial.c
> > > > @@ -575,6 +575,21 @@ static void serial_omap_rdi(struct uart_omap_port *up, unsigned int lsr)
> > > >  }
> > > >  
> > > >  /**
> > > > + * serial_omap_fast_irq() - schedule interrupt handling
> > > > + */
> > > > +static irqreturn_t serial_omap_fast_irq(int irq, void *dev_id)
> > > > +{
> > > > +	struct uart_omap_port *up = dev_id;
> > > > +	unsigned int iir = serial_in(up, UART_IIR);
> > > > +
> > > > +	if (iir & UART_IIR_NO_INT)
> > > > +		return IRQ_NONE;
> > > > +
> > > > +	disable_irq_nosync(up->port.irq);
> > > 
> > > NAK. Either use IRQF_ONESHOT or actually mask the IRQs at the device's
> > > registers (basically clearing IER).
> > 
> > Given the work that's been done on the 8250 based driver, what are the
> > short-term chances omap-serial will be dropped? I'd be happy to improve
> > here if it makes sense to do so. If the 8250 based driver is going to
> > replace omap-serial anyway on the short term, I don't see the point of
> > further developing this patch. The others would still make sense in my
> > opinion.
> 
> if we find a way to maintain the same ttyO* naming scheme and make it
> coexist with ttyS* naming, then we could drop as soon as 8250_omap is
> ready for prime time.

With that in mind, for now I'll be betting on two horses.

I'll cook up a new version using oneshot.

Thanks,
Frans

[RFC PATCH 3/4] tty: omap-serial: use threaded interrupt handler

[Felipe Balbi]

Hi,

On Thu, Aug 21, 2014 at 11:41:17PM +0200, Frans Klaver wrote:
> On Wed, Aug 20, 2014 at 11:06:05AM -0500, Felipe Balbi wrote:
> > On Wed, Aug 20, 2014 at 08:40:28AM +0200, Frans Klaver wrote:
> > > On Tue, Aug 19, 2014 at 01:57:02PM -0500, Felipe Balbi wrote:
> > > > On Tue, Aug 19, 2014 at 02:14:47PM +0200, Frans Klaver wrote:
> > > > > At 3.6Mbaud, with slightly over 2Mbit/s data coming in, we see 1600 uart
> > > > > rx buffer overflows within 30 seconds. Threading the interrupt handling reduces
> > > > > this to about 170 overflows in 10 minutes.
> > > > 
> > > > Can you try Sebastian Siewior's patches for 8250_omap and 8250 dma
> > > > support ? That should help you a lot.
> > > 
> > > I'll have a look at that series. Thanks for pointing it out.
> 
> I have had a look at Sebastian's series, but I'm not convinced
> yet that we should use it. So far the serial console seems to be
> missing data every now and then. I haven't gotten around to testing our
> high traffic application yet.

as any new driver, there are bugs to be fixed. How about reporting the
ones you found together with a way of reproducing them so they can be
fixed ?

cheers

-- 
balbi
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[RFC PATCH 3/4] tty: omap-serial: use threaded interrupt handler

[Frans Klaver]

On August 21, 2014 11:48:40 PM CEST, Felipe Balbi <balbi@ti.com> wrote:
>Hi,
>
>On Thu, Aug 21, 2014 at 11:41:17PM +0200, Frans Klaver wrote:
>> On Wed, Aug 20, 2014 at 11:06:05AM -0500, Felipe Balbi wrote:
>> > On Wed, Aug 20, 2014 at 08:40:28AM +0200, Frans Klaver wrote:
>> > > On Tue, Aug 19, 2014 at 01:57:02PM -0500, Felipe Balbi wrote:
>> > > > On Tue, Aug 19, 2014 at 02:14:47PM +0200, Frans Klaver wrote:
>> > > > > At 3.6Mbaud, with slightly over 2Mbit/s data coming in, we
>see 1600 uart
>> > > > > rx buffer overflows within 30 seconds. Threading the
>interrupt handling reduces
>> > > > > this to about 170 overflows in 10 minutes.
>> > > > 
>> > > > Can you try Sebastian Siewior's patches for 8250_omap and 8250
>dma
>> > > > support ? That should help you a lot.
>> > > 
>> > > I'll have a look at that series. Thanks for pointing it out.
>> 
>> I have had a look at Sebastian's series, but I'm not convinced
>> yet that we should use it. So far the serial console seems to be
>> missing data every now and then. I haven't gotten around to testing
>our
>> high traffic application yet.
>
>as any new driver, there are bugs to be fixed. How about reporting the
>ones you found together with a way of reproducing them so they can be
>fixed ?

Yes, definitely.

Cheers, 
Frans

[RFC PATCH 3/4] tty: omap-serial: use threaded interrupt handler

[Frans Klaver]

At 3.6Mbaud, with slightly over 2Mbit/s data coming in, we see 1600 uart
rx buffer overflows within 30 seconds. Threading the interrupt handling reduces
this to about 170 overflows in 10 minutes.

In practice this therefore reduces the need for hardware flow control,
meaning the sending side doesn't have to buffer as much either.

Signed-off-by: Frans Klaver <frans.klaver@xsens.com>
---
 drivers/tty/serial/omap-serial.c | 30 +++++++++++++++++++++++-------
 1 file changed, 23 insertions(+), 7 deletions(-)

diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
index 14a0167..1671443a 100644
--- a/drivers/tty/serial/omap-serial.c
+++ b/drivers/tty/serial/omap-serial.c
@@ -575,6 +575,20 @@ static void serial_omap_rdi(struct uart_omap_port *up, unsigned int lsr)
 }
 
 /**
+ * serial_omap_fast_irq() - schedule interrupt handling
+ */
+static irqreturn_t serial_omap_fast_irq(int irq, void *dev_id)
+{
+	struct uart_omap_port *up = dev_id;
+	unsigned int iir = serial_in(up, UART_IIR);
+
+	if (iir & UART_IIR_NO_INT)
+		return IRQ_NONE;
+
+	return IRQ_WAKE_THREAD;
+}
+
+/**
  * serial_omap_irq() - This handles the interrupt from one port
  * @irq: uart port irq number
  * @dev_id: uart port info
@@ -584,7 +598,6 @@ static irqreturn_t serial_omap_irq(int irq, void *dev_id)
 	struct uart_omap_port *up = dev_id;
 	unsigned int iir, lsr;
 	unsigned int type;
-	irqreturn_t ret = IRQ_NONE;
 	int max_count = 256;
 
 	spin_lock(&up->port.lock);
@@ -595,7 +608,6 @@ static irqreturn_t serial_omap_irq(int irq, void *dev_id)
 		if (iir & UART_IIR_NO_INT)
 			break;
 
-		ret = IRQ_HANDLED;
 		lsr = serial_in(up, UART_LSR);
 
 		/* extract IRQ type from IIR register */
@@ -634,7 +646,7 @@ static irqreturn_t serial_omap_irq(int irq, void *dev_id)
 	pm_runtime_put_autosuspend(up->dev);
 	up->port_activity = jiffies;
 
-	return ret;
+	return IRQ_HANDLED;
 }
 
 static unsigned int serial_omap_tx_empty(struct uart_port *port)
@@ -731,15 +743,19 @@ static int serial_omap_startup(struct uart_port *port)
 	/*
 	 * Allocate the IRQ
 	 */
-	retval = request_irq(up->port.irq, serial_omap_irq, up->port.irqflags,
-				up->name, up);
+	retval = request_threaded_irq(up->port.irq, serial_omap_fast_irq,
+						serial_omap_irq,
+						IRQF_ONESHOT | up->port.irqflags,
+						up->name, up);
 	if (retval)
 		return retval;
 
 	/* Optional wake-up IRQ */
 	if (up->wakeirq) {
-		retval = request_irq(up->wakeirq, serial_omap_irq,
-				     up->port.irqflags, up->name, up);
+		retval = request_threaded_irq(up->wakeirq, serial_omap_fast_irq,
+						serial_omap_irq,
+						IRQF_ONESHOT | up->port.irqflags,
+						up->name, up);
 		if (retval) {
 			free_irq(up->port.irq, up);
 			return retval;
-- 
1.9.3

[PATCH 4/4] tty: omap-serial: support setting of hardware flow control in dts

[Frans Klaver]

This makes hardware flow control availability configurable from the
device tree.

Signed-off-by: Frans Klaver <frans.klaver@xsens.com>
---
 Documentation/devicetree/bindings/serial/omap_serial.txt | 1 +
 drivers/tty/serial/omap-serial.c                         | 4 ++++
 2 files changed, 5 insertions(+)

diff --git a/Documentation/devicetree/bindings/serial/omap_serial.txt b/Documentation/devicetree/bindings/serial/omap_serial.txt
index 342eedd..1b629e9 100644
--- a/Documentation/devicetree/bindings/serial/omap_serial.txt
+++ b/Documentation/devicetree/bindings/serial/omap_serial.txt
@@ -8,3 +8,4 @@ Required properties:
 
 Optional properties:
 - clock-frequency : frequency of the clock input to the UART
+- has-hw-flow-control : the hardware has flow control capability
diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
index 57664b9..7d3b3d2 100644
--- a/drivers/tty/serial/omap-serial.c
+++ b/drivers/tty/serial/omap-serial.c
@@ -1598,6 +1598,10 @@ static struct omap_uart_port_info *of_get_uart_port_info(struct device *dev)
 
 	of_property_read_u32(dev->of_node, "clock-frequency",
 					 &omap_up_info->uartclk);
+
+	if (of_property_read_bool(dev->of_node, "has-hw-flow-control"))
+		omap_up_info->flags |= UPF_HARD_FLOW;
+
 	return omap_up_info;
 }
 
-- 
1.9.3