[PATCH V3] serial/uart/8250: Add tunable RX interrupt trigger I/F of FIFO buffers

[PATCH V3] serial/uart/8250: Add tunable RX interrupt trigger I/F of FIFO buffers

[Yoshihiro YUNOMAE]

Add tunable RX interrupt trigger I/F of FIFO buffers.
Serial devices are used as not only message communication devices but control
or sending communication devices. For the latter uses, normally small data
will be exchanged, so user applications want to receive data unit as soon as
possible for real-time tendency. If we have a sensor which sends a 1 byte data
each time and must control a device based on the sensor feedback, the RX
interrupt should be triggered for each data.

According to HW specification of serial UART devices, RX interrupt trigger
can be changed, but the trigger is hard-coded. For example, RX interrupt trigger
in 16550A can be set to 1, 4, 8, or 14 bytes for HW, but current driver sets
the trigger to only 8bytes.

This patch makes a 16550A device change RX interrupt trigger from userland.

<How to use>
- Read current setting
 # cat /sys/dev/char/4\:64/rx_int_trig
 8

- Write user setting
 # echo 1 > /sys/dev/char/4\:64/rx_int_trig
 # cat /sys/dev/char/4\:64/rx_int_trig
 1

<Support uart device>
- 16550A (1, 4, 8, or 14 bytes)

Changed in V2:
 - Use _IOW for TIOCSFIFORTRIG definition
 - Pass the interrupt trigger value itself

Changes in V3:
 - Change I/F from ioctl(2) to sysfs(rx_int_trig)

Signed-off-by: Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Cc: Jingoo Han <jg1.han@samsung.com>
Cc: Aaron Sierra <asierra@xes-inc.com>
Cc: Stephen Warren <swarren@nvidia.com>
Cc: linux-serial@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
 drivers/tty/serial/8250/8250_core.c |  189 ++++++++++++++++++++++++++++++++++-
 drivers/tty/serial/serial_core.c    |   18 ++-
 include/linux/serial_8250.h         |    1 
 include/linux/serial_core.h         |    4 +
 4 files changed, 198 insertions(+), 14 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
index 69932b7..c945ceb 100644
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -531,11 +531,9 @@ static void serial8250_clear_fifos(struct uart_8250_port *p)
 
 void serial8250_clear_and_reinit_fifos(struct uart_8250_port *p)
 {
-	unsigned char fcr;
-
 	serial8250_clear_fifos(p);
-	fcr = uart_config[p->port.type].fcr;
-	serial_out(p, UART_FCR, fcr);
+	p->fcr = uart_config[p->port.type].fcr;
+	serial_out(p, UART_FCR, p->fcr);
 }
 EXPORT_SYMBOL_GPL(serial8250_clear_and_reinit_fifos);
 
@@ -2325,10 +2323,19 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
 		if ((baud < 2400 && !up->dma) || fifo_bug) {
 			fcr &= ~UART_FCR_TRIGGER_MASK;
 			fcr |= UART_FCR_TRIGGER_1;
+			/* Don't use user setting RX trigger */
+			up->fcr = 0;
 		}
 	}
 
 	/*
+	 * If up->fcr exists, a user has opened this port, changed RX trigger,
+	 * or read RX trigger before. So, we don't need to change up->fcr here.
+	 */
+	if (!up->fcr)
+		up->fcr = fcr;
+
+	/*
 	 * MCR-based auto flow control.  When AFE is enabled, RTS will be
 	 * deasserted when the receive FIFO contains more characters than
 	 * the trigger, or the MCR RTS bit is cleared.  In the case where
@@ -2455,15 +2462,15 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
 	 * is written without DLAB set, this mode will be disabled.
 	 */
 	if (port->type == PORT_16750)
-		serial_port_out(port, UART_FCR, fcr);
+		serial_port_out(port, UART_FCR, up->fcr);
 
 	serial_port_out(port, UART_LCR, cval);		/* reset DLAB */
 	up->lcr = cval;					/* Save LCR */
 	if (port->type != PORT_16750) {
 		/* emulated UARTs (Lucent Venus 167x) need two steps */
-		if (fcr & UART_FCR_ENABLE_FIFO)
+		if (up->fcr & UART_FCR_ENABLE_FIFO)
 			serial_port_out(port, UART_FCR, UART_FCR_ENABLE_FIFO);
-		serial_port_out(port, UART_FCR, fcr);		/* set fcr */
+		serial_port_out(port, UART_FCR, up->fcr);	/* set fcr */
 	}
 	serial8250_set_mctrl(port, port->mctrl);
 	spin_unlock_irqrestore(&port->lock, flags);
@@ -2656,6 +2663,172 @@ static int serial8250_request_port(struct uart_port *port)
 	return ret;
 }
 
+static unsigned char convert_fcr2val(struct uart_8250_port *up,
+				     unsigned char fcr)
+{
+	unsigned char val = 0, trig_raw = fcr & UART_FCR_TRIGGER_MASK;
+
+	switch (up->port.type) {
+	case PORT_16550A:
+		if (trig_raw == UART_FCR_R_TRIG_00)
+			val = 1;
+		else if (trig_raw == UART_FCR_R_TRIG_01)
+			val = 4;
+		else if (trig_raw == UART_FCR_R_TRIG_10)
+			val = 8;
+		else if (trig_raw == UART_FCR_R_TRIG_11)
+			val = 14;
+		break;
+	}
+	return val;
+}
+
+static int convert_val2rxtrig(struct uart_8250_port *up, unsigned char val)
+{
+	switch (up->port.type) {
+	case PORT_16550A:
+		if (val == 1)
+			return UART_FCR_R_TRIG_00;
+		else if (val == 4)
+			return UART_FCR_R_TRIG_01;
+		else if (val == 8)
+			return UART_FCR_R_TRIG_10;
+		else if (val == 14)
+			return UART_FCR_R_TRIG_11;
+		break;
+	default:
+		pr_info("Not support RX-trigger setting for this serial %u\n",
+			up->port.type);
+	}
+	return -EINVAL;
+}
+
+static unsigned char do_get_rx_int_trig(struct tty_port *port)
+{
+	struct uart_state *state = container_of(port, struct uart_state, port);
+	struct uart_port *uport = state->uart_port;
+	struct uart_8250_port *up =
+		container_of(uport, struct uart_8250_port, port);
+
+	if (!(up->capabilities & UART_CAP_FIFO) || uport->fifosize <= 1)
+		return 0;
+
+	if (!up->fcr)
+		/* termios is not set yet */
+		up->fcr = uart_config[up->port.type].fcr;
+
+	return convert_fcr2val(up, up->fcr);
+}
+
+static unsigned char do_serial8250_get_rx_int_trig(struct tty_port *port)
+{
+	unsigned char rx_trig_byte;
+
+	mutex_lock(&port->mutex);
+	rx_trig_byte = do_get_rx_int_trig(port);
+	mutex_unlock(&port->mutex);
+
+	return rx_trig_byte;
+}
+
+static ssize_t serial8250_get_attr_rx_int_trig(struct device *dev,
+	struct device_attribute *attr, char *buf)
+{
+	struct tty_port *port = dev_get_drvdata(dev);
+	unsigned char rx_trig_byte;
+
+	rx_trig_byte = do_serial8250_get_rx_int_trig(port);
+	/* rx_trig_byte == 0 means RX interrupt trigger is undefined */
+	if (!rx_trig_byte)
+		return -EINVAL;
+
+	return snprintf(buf, PAGE_SIZE, "%u\n", rx_trig_byte);
+}
+
+static int do_set_rx_int_trig(struct tty_port *port, unsigned char val)
+{
+	struct uart_state *state = container_of(port, struct uart_state, port);
+	struct uart_port *uport = state->uart_port;
+	struct uart_8250_port *up =
+		container_of(uport, struct uart_8250_port, port);
+	unsigned char fcr;
+	int rx_trig;
+
+	if (!(up->capabilities & UART_CAP_FIFO) || uport->fifosize <= 1)
+		return -EINVAL;
+
+	rx_trig = convert_val2rxtrig(up, val);
+	if (rx_trig < 0)
+		return rx_trig;
+
+	serial8250_clear_fifos(up);
+	if (!up->fcr)
+		/* termios is not set yet */
+		fcr = uart_config[up->port.type].fcr;
+	else
+		fcr = up->fcr;
+	fcr &= ~UART_FCR_TRIGGER_MASK;
+	fcr |= (unsigned char)rx_trig;
+	up->fcr = fcr;
+	serial_out(up, UART_FCR, up->fcr);
+	return 0;
+}
+
+static int do_serial8250_set_rx_int_trig(struct tty_port *port,
+					 unsigned char val)
+{
+	int ret;
+
+	mutex_lock(&port->mutex);
+	ret = do_set_rx_int_trig(port, val);
+	mutex_unlock(&port->mutex);
+
+	return ret;
+}
+
+static ssize_t serial8250_set_attr_rx_int_trig(struct device *dev,
+	struct device_attribute *attr, const char *buf, size_t count)
+{
+	struct tty_port *port = dev_get_drvdata(dev);
+	unsigned char val;
+	int ret;
+
+	if (!count)
+		return -EINVAL;
+
+	ret = kstrtou8(buf, 10, &val);
+	if (ret < 0)
+		return ret;
+
+	ret = do_serial8250_set_rx_int_trig(port, val);
+	if (ret < 0)
+		return ret;
+
+	return count;
+}
+
+static DEVICE_ATTR(rx_int_trig, S_IRUSR | S_IWUSR | S_IRGRP,
+		   serial8250_get_attr_rx_int_trig,
+		   serial8250_set_attr_rx_int_trig);
+
+static struct attribute *serial8250_dev_attrs[] = {
+	&dev_attr_rx_int_trig.attr,
+	NULL,
+	};
+
+static struct attribute_group serial8250_dev_attr_group = {
+	.attrs = serial8250_dev_attrs,
+	};
+
+static void register_dev_spec_attr_grp(struct uart_8250_port *up)
+{
+	switch (up->port.type) {
+	case PORT_16550A:
+		up->port.dev_spec_attr_group = &serial8250_dev_attr_group;
+		break;
+	}
+}
+
 static void serial8250_config_port(struct uart_port *port, int flags)
 {
 	struct uart_8250_port *up =
@@ -2704,6 +2877,8 @@ static void serial8250_config_port(struct uart_port *port, int flags)
 	if ((port->type == PORT_XR17V35X) ||
 	   (port->type == PORT_XR17D15X))
 		port->handle_irq = exar_handle_irq;
+
+	register_dev_spec_attr_grp(up);
 }
 
 static int
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index ece2049..5cfa732 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -2548,15 +2548,16 @@ static struct attribute *tty_dev_attrs[] = {
 	NULL,
 	};
 
-static const struct attribute_group tty_dev_attr_group = {
+static struct attribute_group tty_dev_attr_group = {
 	.attrs = tty_dev_attrs,
 	};
 
-static const struct attribute_group *tty_dev_attr_groups[] = {
-	&tty_dev_attr_group,
-	NULL
-	};
-
+static void make_uport_attr_grps(struct uart_port *uport)
+{
+	uport->attr_grps[0] = &tty_dev_attr_group;
+	if (uport->dev_spec_attr_group)
+		uport->attr_grps[1] = uport->dev_spec_attr_group;
+}
 
 /**
  *	uart_add_one_port - attach a driver-defined port structure
@@ -2607,12 +2608,15 @@ int uart_add_one_port(struct uart_driver *drv, struct uart_port *uport)
 
 	uart_configure_port(drv, state, uport);
 
+	make_uport_attr_grps(uport);
+
 	/*
 	 * Register the port whether it's detected or not.  This allows
 	 * setserial to be used to alter this ports parameters.
 	 */
 	tty_dev = tty_port_register_device_attr(port, drv->tty_driver,
-			uport->line, uport->dev, port, tty_dev_attr_groups);
+			uport->line, uport->dev, port,
+			(const struct attribute_group **)uport->attr_grps);
 	if (likely(!IS_ERR(tty_dev))) {
 		device_set_wakeup_capable(tty_dev, 1);
 	} else {
diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h
index af47a8a..2ce1152 100644
--- a/include/linux/serial_8250.h
+++ b/include/linux/serial_8250.h
@@ -76,6 +76,7 @@ struct uart_8250_port {
 	unsigned short		bugs;		/* port bugs */
 	unsigned int		tx_loadsz;	/* transmit fifo load size */
 	unsigned char		acr;
+	unsigned char		fcr;
 	unsigned char		ier;
 	unsigned char		lcr;
 	unsigned char		mcr;
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index f729be9..7e3122f 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -113,6 +113,8 @@ struct uart_icount {
 
 typedef unsigned int __bitwise__ upf_t;
 
+#define MAX_ATTR_GRPS		3
+
 struct uart_port {
 	spinlock_t		lock;			/* port lock */
 	unsigned long		iobase;			/* in/out[bwl] */
@@ -195,6 +197,8 @@ struct uart_port {
 	unsigned int		line;			/* port index */
 	resource_size_t		mapbase;		/* for ioremap */
 	struct device		*dev;			/* parent device */
+	struct attribute_group	*dev_spec_attr_group;	/* specific attribute */
+	struct attribute_group	*attr_grps[MAX_ATTR_GRPS];/* all attr. groups */
 	unsigned char		hub6;			/* this should be in the 8250 driver */
 	unsigned char		suspended;
 	unsigned char		irq_wake;

Re: [PATCH V3] serial/uart/8250: Add tunable RX interrupt trigger I/F of FIFO buffers

[One Thousand Gnomes]

> @@ -2325,10 +2323,19 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
>  		if ((baud < 2400 && !up->dma) || fifo_bug) {
>  			fcr &= ~UART_FCR_TRIGGER_MASK;
>  			fcr |= UART_FCR_TRIGGER_1;
> +			/* Don't use user setting RX trigger */
> +			up->fcr = 0;

This breaks

	set fcr via sysfs
	set baud rate below 2400
	set baud rate higher

If baud < 2400 and the user has set a value then probably we should honour
it. If fifo_bug is set then we should never honour it (and should perhaps
eventually error it in the sysfs set).


> +static unsigned char convert_fcr2val(struct uart_8250_port *up,
> +				     unsigned char fcr)
> +{
> +	unsigned char val = 0, trig_raw = fcr & UART_FCR_TRIGGER_MASK;
> +
> +	switch (up->port.type) {
> +	case PORT_16550A:
> +		if (trig_raw == UART_FCR_R_TRIG_00)
> +			val = 1;
> +		else if (trig_raw == UART_FCR_R_TRIG_01)
> +			val = 4;
> +		else if (trig_raw == UART_FCR_R_TRIG_10)
> +			val = 8;
> +		else if (trig_raw == UART_FCR_R_TRIG_11)
> +			val = 14;
> +		break;

Surely the default case should be returning 1 not 0 ?


> +static int convert_val2rxtrig(struct uart_8250_port *up, unsigned char val)
> +{
> +	switch (up->port.type) {
> +	case PORT_16550A:
> +		if (val == 1)
> +			return UART_FCR_R_TRIG_00;
> +		else if (val == 4)
> +			return UART_FCR_R_TRIG_01;
> +		else if (val == 8)
> +			return UART_FCR_R_TRIG_10;
> +		else if (val == 14)
> +			return UART_FCR_R_TRIG_11;

What happens if you specify a meaningless value. Doing exact matching
means that you have to know the hardware exactly. How about

	if (val < 4)
		return UART_FCR_R_TRIG_00;
	else if (val < 8)
		return UART_FCR_R_TRIG_01;
	else if (val < 14)
		return UART_FCR_R_TRIG_10;
	else
		return UART_FCR_R_TRIG_11;

so you get the nearest lower value that the hardware can provide ?

> +		break;
> +	default:
> +		pr_info("Not support RX-trigger setting for this serial %u\n",
> +			up->port.type);

That lets users spew into the logs. I think actually you just want

	default:
		return -EOPNOTSUPP;

or similar



Otherwise this looks good to me. The interface is sensible, it can be
expanded easily to other devices and device types, and the logic looks
right.

Alan

Re: [PATCH V3] serial/uart/8250: Add tunable RX interrupt trigger I/F of FIFO buffers

[Heikki Krogerus]

On Fri, Mar 14, 2014 at 12:04:00PM +0000, One Thousand Gnomes wrote:
> Otherwise this looks good to me. The interface is sensible, it can be
> expanded easily to other devices and device types, and the logic looks
> right.

I have one concern..

I think this may be problematic when used with DMA. The burst size is
usually expected to be aligned with the trigger level.

Though I don't know how big risk that actually is.


Thanks,

-- 
heikki

Re: Re: [PATCH V3] serial/uart/8250: Add tunable RX interrupt trigger I/F of FIFO buffers

[Yoshihiro YUNOMAE]

Hi Alan,

Thank you for your reply.

(2014/03/14 21:04), One Thousand Gnomes wrote:
>> @@ -2325,10 +2323,19 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
>>   		if ((baud < 2400 && !up->dma) || fifo_bug) {
>>   			fcr &= ~UART_FCR_TRIGGER_MASK;
>>   			fcr |= UART_FCR_TRIGGER_1;
>> +			/* Don't use user setting RX trigger */
>> +			up->fcr = 0;
>
> This breaks
>
> 	set fcr via sysfs
> 	set baud rate below 2400
> 	set baud rate higher
>
> If baud < 2400 and the user has set a value then probably we should honour

OK, I'll add !up->fcr in this flow as follows:

/* NOTE: If fifo_bug is not set, a user can set RX trigger. */
if ((baud < 2400 && !up->dma && !up->fcr) || fifo_bug) {
      fcr &= ~UART_TRIGGER_MASK;
      fcr |= UART_FCR_TRIGGER_1;
      up->fcr = 0;
}

> it. If fifo_bug is set then we should never honour it (and should perhaps
> eventually error it in the sysfs set).

When fifo_bug is set to "1", we need to check not only
whether (up->bugs & UART_BUG_PARITY) but whether parity is enabled.
We can check whether parity is enable only in this function currently,
so I think we need to store fifo_bug's value into up->fifo_bug and
refer it in the sysfs set(do_set_rx_int_trig()) as follows:

@do_set_rx_int_trig()
     if (!(up->capabilities & UART_CAP_FIFO) || uport->fifosize <= 1
         || (up->fifo_bug & UART_BUG_PARITY))
         return -EINVAL;

>
>> +static unsigned char convert_fcr2val(struct uart_8250_port *up,
>> +				     unsigned char fcr)
>> +{
>> +	unsigned char val = 0, trig_raw = fcr & UART_FCR_TRIGGER_MASK;
>> +
>> +	switch (up->port.type) {
>> +	case PORT_16550A:
>> +		if (trig_raw == UART_FCR_R_TRIG_00)
>> +			val = 1;
>> +		else if (trig_raw == UART_FCR_R_TRIG_01)
>> +			val = 4;
>> +		else if (trig_raw == UART_FCR_R_TRIG_10)
>> +			val = 8;
>> +		else if (trig_raw == UART_FCR_R_TRIG_11)
>> +			val = 14;
>> +		break;
>
> Surely the default case should be returning 1 not 0 ?

In the default case, it returns "0" meaning error because "1" has
other meaning (1 byte RX trigger). But, "0" is not instinctive value for
the error, so it should return -EOPNOTSUPP here.

>
>> +static int convert_val2rxtrig(struct uart_8250_port *up, unsigned char val)
>> +{
>> +	switch (up->port.type) {
>> +	case PORT_16550A:
>> +		if (val == 1)
>> +			return UART_FCR_R_TRIG_00;
>> +		else if (val == 4)
>> +			return UART_FCR_R_TRIG_01;
>> +		else if (val == 8)
>> +			return UART_FCR_R_TRIG_10;
>> +		else if (val == 14)
>> +			return UART_FCR_R_TRIG_11;
>
> What happens if you specify a meaningless value. Doing exact matching
> means that you have to know the hardware exactly. How about
>
> 	if (val < 4)
> 		return UART_FCR_R_TRIG_00;
> 	else if (val < 8)
> 		return UART_FCR_R_TRIG_01;
> 	else if (val < 14)
> 		return UART_FCR_R_TRIG_10;
> 	else
> 		return UART_FCR_R_TRIG_11;
>
> so you get the nearest lower value that the hardware can provide ?

It is a good idea. I was concerned about the same thing which users
must know the HW exactly.

I'll implement it as you say.

>> +		break;
>> +	default:
>> +		pr_info("Not support RX-trigger setting for this serial %u\n",
>> +			up->port.type);
>
> That lets users spew into the logs. I think actually you just want
>
> 	default:
> 		return -EOPNOTSUPP;

OK, I'll use this.

Thank you,

Yoshihiro YUNOMAE

-- 
Yoshihiro YUNOMAE
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: yoshihiro.yunomae.ez@hitachi.com

Re: [PATCH V3] serial/uart/8250: Add tunable RX interrupt trigger I/F of FIFO buffers

[Heikki Krogerus]

Hi,

On Fri, Mar 14, 2014 at 11:21:54AM +0900, Yoshihiro YUNOMAE wrote:
>  void serial8250_clear_and_reinit_fifos(struct uart_8250_port *p)
>  {
> -	unsigned char fcr;
> -
>  	serial8250_clear_fifos(p);
> -	fcr = uart_config[p->port.type].fcr;
> -	serial_out(p, UART_FCR, fcr);
> +	p->fcr = uart_config[p->port.type].fcr;
> +	serial_out(p, UART_FCR, p->fcr);

You should allow also the probe drivers to set this..

        if (!p->fcr)
                p->fcr = uart_config[p->port.type].fcr;

>  }
>  EXPORT_SYMBOL_GPL(serial8250_clear_and_reinit_fifos);
>  
> @@ -2325,10 +2323,19 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
>  		if ((baud < 2400 && !up->dma) || fifo_bug) {
>  			fcr &= ~UART_FCR_TRIGGER_MASK;
>  			fcr |= UART_FCR_TRIGGER_1;
> +			/* Don't use user setting RX trigger */
> +			up->fcr = 0;

I don't know about this but..

>  		}
>  	}
>  
>  	/*
> +	 * If up->fcr exists, a user has opened this port, changed RX trigger,
> +	 * or read RX trigger before. So, we don't need to change up->fcr here.
> +	 */
> +	if (!up->fcr)
> +		up->fcr = fcr;

Why not just set fcr = up->fcr in the beginning of the function?

<snip>

> +static int do_set_rx_int_trig(struct tty_port *port, unsigned char val)
> +{
> +	struct uart_state *state = container_of(port, struct uart_state, port);
> +	struct uart_port *uport = state->uart_port;
> +	struct uart_8250_port *up =
> +		container_of(uport, struct uart_8250_port, port);
> +	unsigned char fcr;
> +	int rx_trig;
> +
> +	if (!(up->capabilities & UART_CAP_FIFO) || uport->fifosize <= 1)
> +		return -EINVAL;
> +
> +	rx_trig = convert_val2rxtrig(up, val);
> +	if (rx_trig < 0)
> +		return rx_trig;
> +
> +	serial8250_clear_fifos(up);
> +	if (!up->fcr)
> +		/* termios is not set yet */
> +		fcr = uart_config[up->port.type].fcr;
> +	else
> +		fcr = up->fcr;
> +	fcr &= ~UART_FCR_TRIGGER_MASK;
> +	fcr |= (unsigned char)rx_trig;
> +	up->fcr = fcr;
> +	serial_out(up, UART_FCR, up->fcr);
> +	return 0;
> +}

Where are you setting UART_FCR_ENABLE_FIFO bit? Am I missing
something?

> diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h
> index af47a8a..2ce1152 100644
> --- a/include/linux/serial_8250.h
> +++ b/include/linux/serial_8250.h
> @@ -76,6 +76,7 @@ struct uart_8250_port {
>  	unsigned short		bugs;		/* port bugs */
>  	unsigned int		tx_loadsz;	/* transmit fifo load size */
>  	unsigned char		acr;
> +	unsigned char		fcr;

I do like to see fcr being added here, but because of a different
reason. I want to be able to set it from the probe drivers.

Br,

-- 
heikki

Re: Re: [PATCH V3] serial/uart/8250: Add tunable RX interrupt trigger I/F of FIFO buffers

[Yoshihiro YUNOMAE]

Hi Heikki,

Thank you for your reply.

(2014/03/14 23:16), Heikki Krogerus wrote:
> Hi,
>
> On Fri, Mar 14, 2014 at 11:21:54AM +0900, Yoshihiro YUNOMAE wrote:
>>   void serial8250_clear_and_reinit_fifos(struct uart_8250_port *p)
>>   {
>> -	unsigned char fcr;
>> -
>>   	serial8250_clear_fifos(p);
>> -	fcr = uart_config[p->port.type].fcr;
>> -	serial_out(p, UART_FCR, fcr);
>> +	p->fcr = uart_config[p->port.type].fcr;
>> +	serial_out(p, UART_FCR, p->fcr);
>
> You should allow also the probe drivers to set this..
>
>          if (!p->fcr)
>                  p->fcr = uart_config[p->port.type].fcr;

Oh, I'll fix it.

>>   }
>>   EXPORT_SYMBOL_GPL(serial8250_clear_and_reinit_fifos);
>>
>> @@ -2325,10 +2323,19 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
>>   		if ((baud < 2400 && !up->dma) || fifo_bug) {
>>   			fcr &= ~UART_FCR_TRIGGER_MASK;
>>   			fcr |= UART_FCR_TRIGGER_1;
>> +			/* Don't use user setting RX trigger */
>> +			up->fcr = 0;
>
> I don't know about this but..
>
>>   		}
>>   	}
>>
>>   	/*
>> +	 * If up->fcr exists, a user has opened this port, changed RX trigger,
>> +	 * or read RX trigger before. So, we don't need to change up->fcr here.
>> +	 */
>> +	if (!up->fcr)
>> +		up->fcr = fcr;
>
> Why not just set fcr = up->fcr in the beginning of the function?

Ah, we don't need to set up->fcr = 0 in the previous flow when we
implement as follows:

unsigned char fcr = up->fcr;

  ... <snip> ...

     /*
      * If fcr exists, a user has opened this port, changed RX
      * trigger, or read RX trigger before. If so, we do not change
      * fcr.
      */
     if (!fcr)
         fcr = uart_config[port_type].fcr;
     if ((baud < 2400 && !up->dma) || fifo_bug) {
         fcr &= ~UART_FCR_TRIGGER_MASK;
         fcr |= UART_FCR_TRIGGER_1;
     }

up->fcr = fcr;

> <snip>
>
>> +static int do_set_rx_int_trig(struct tty_port *port, unsigned char val)
>> +{
>> +	struct uart_state *state = container_of(port, struct uart_state, port);
>> +	struct uart_port *uport = state->uart_port;
>> +	struct uart_8250_port *up =
>> +		container_of(uport, struct uart_8250_port, port);
>> +	unsigned char fcr;
>> +	int rx_trig;
>> +
>> +	if (!(up->capabilities & UART_CAP_FIFO) || uport->fifosize <= 1)
>> +		return -EINVAL;
>> +
>> +	rx_trig = convert_val2rxtrig(up, val);
>> +	if (rx_trig < 0)
>> +		return rx_trig;
>> +
>> +	serial8250_clear_fifos(up);
>> +	if (!up->fcr)
>> +		/* termios is not set yet */
>> +		fcr = uart_config[up->port.type].fcr;
>> +	else
>> +		fcr = up->fcr;
>> +	fcr &= ~UART_FCR_TRIGGER_MASK;
>> +	fcr |= (unsigned char)rx_trig;
>> +	up->fcr = fcr;
>> +	serial_out(up, UART_FCR, up->fcr);
>> +	return 0;
>> +}
>
> Where are you setting UART_FCR_ENABLE_FIFO bit? Am I missing
> something?

In these implementation, the driver sets up->fcr as
uart_config[up->port.type].fcr first and changes only RX trigger. So,
we don't need to set the bit in a direct way.

Thank you,
Yoshihiro YUNOMAE

-- 
Yoshihiro YUNOMAE
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: yoshihiro.yunomae.ez@hitachi.com