serial/uart/8250: Add tunable RX interrupt trigger I/F of FIFO buffers

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 some devices change RX interrupt trigger from userland.

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 some devices 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 devices>
- 16550A and Tegra (1, 4, 8, or 14 bytes)
- 16650V2 (8, 16, 24, or 28 bytes)
- 16654 (8, 16, 56, or 60 bytes)
- 16750 (1, 16, 32, or 56 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)

Changes in V4:
- Introduce fifo_bug flag in uart_8250_port structure
This is enabled only when parity is enabled and UART_BUG_PARITY is enabled for up->bugs. If this flag is enabled, user cannot set RX trigger.
- Return -EOPNOTSUPP when it does not support device at convert_fcr2val() and at convert_val2rxtrig()
- Set the nearest lower RX trigger when users input a meaningless value at convert_val2rxtrig()
- Check whether p->fcr is existing at serial8250_clear_and_reinit_fifos()
- Set fcr = up->fcr in the begging of serial8250_do_set_termios()

Changes in V5:
- Support Tegra, 16650V2, 16654, and 16750
- Store default FCR value to up->fcr when the port is first created
- Add rx_trig_byte[] in uart_config[] for each device and use rx_trig_byte[] in convert_fcr2val() and convert_val2rxtrig()

Changes in V5.1:
- Fix FCR_RX_TRIG_MAX_STATE definition

Changes in V6:
- Move FCR_RX_TRIG_* definition in 8250.h to include/uapi/linux/serial_reg.h, rename those to UART_FCR_R_TRIG_*, and use UART_FCR_TRIGGER_MASK to UART_FCR_R_TRIG_BITS()
- Change following function names:
convert_fcr2val() => fcr_get_rxtrig_bytes() convert_val2rxtrig() => bytes_to_fcr_rxtrig()
- Fix typo in serial8250_do_set_termios()
- Delete the verbose error message pr_info() in bytes_to_fcr_rxtrig()
- Rename *rx_int_trig/rx_trig* to *rxtrig* for several functions or variables (but UI remains rx_int_trig)
- Change the meaningless variable name 'val' to 'bytes' following functions:

    fcr_get_rxtrig_bytes(), bytes_to_fcr_rxtrig(), do_set_rxtrig(),
    do_serial8250_set_rxtrig(), and serial8250_set_attr_rxtrig()

- Use up->fcr in order to get rxtrig_bytes instead of rx_trig_raw in fcr_get_rxtrig_bytes()
- Use conf_type->rxtrig_bytes[0] instead of switch statement for support check in register_dev_spec_attr_grp()
- Delete the checking whether a user changed FCR or not when minimum buffer is needed in serial8250_do_set_termios()

Signed-off-by Yoshihiro YUNOMAE <[email protected]>

Cc Greg Kroah-Hartman <[email protected]>

Cc Jiri Slaby <[email protected]>

Cc Heikki Krogerus <[email protected]>

Cc Jingoo Han <[email protected]>

Cc Aaron Sierra <[email protected]>

Reviewed-by Stephen Warren <[email protected]>

---
 drivers/tty/serial/8250/8250.h      |    2 
 drivers/tty/serial/8250/8250_core.c |  173 ++++++++++++++++++++++++++++++++---
 drivers/tty/serial/serial_core.c    |   18 ++--
 include/linux/serial_8250.h         |    2 
 include/linux/serial_core.h         |    4 +
 include/uapi/linux/serial_reg.h     |    5 +
 6 files changed, 182 insertions(+), 22 deletions(-)

drivers/tty/serial/8250/8250.h +2 -0

index 1ebf853..1b08c91 100644
@@ -12,6 +12,7 @@
  */
 
 #include <linux/serial_8250.h>
+#include <linux/serial_reg.h>
 #include <linux/dmaengine.h>
 
 struct uart_8250_dma {

@@ -60,6 +61,7 @@ struct serial8250_config {
 	unsigned short	fifo_size;
 	unsigned short	tx_loadsz;
 	unsigned char	fcr;
+	unsigned char	rxtrig_bytes[UART_FCR_R_TRIG_MAX_STATE];
 	unsigned int	flags;
 };
 

drivers/tty/serial/8250/8250_core.c +128 -15

index 81f909c..fd1b3ec 100644
@@ -31,7 +31,6 @@
 #include <linux/tty.h>
 #include <linux/ratelimit.h>
 #include <linux/tty_flip.h>
-#include <linux/serial_reg.h>
 #include <linux/serial_core.h>
 #include <linux/serial.h>
 #include <linux/serial_8250.h>

@@ -161,6 +160,7 @@ static const struct serial8250_config uart_config[] = {
 		.fifo_size	= 16,
 		.tx_loadsz	= 16,
 		.fcr		= UART_FCR_ENABLE_FIFO | UART_FCR_R_TRIG_10,
+		.rxtrig_bytes	= {1, 4, 8, 14},
 		.flags		= UART_CAP_FIFO,
 	},
 	[PORT_CIRRUS] = {

@@ -180,6 +180,7 @@ static const struct serial8250_config uart_config[] = {
 		.tx_loadsz	= 16,
 		.fcr		= UART_FCR_ENABLE_FIFO | UART_FCR_R_TRIG_01 |
 				  UART_FCR_T_TRIG_00,
+		.rxtrig_bytes	= {8, 16, 24, 28},
 		.flags		= UART_CAP_FIFO | UART_CAP_EFR | UART_CAP_SLEEP,
 	},
 	[PORT_16750] = {

@@ -188,6 +189,7 @@ static const struct serial8250_config uart_config[] = {
 		.tx_loadsz	= 64,
 		.fcr		= UART_FCR_ENABLE_FIFO | UART_FCR_R_TRIG_10 |
 				  UART_FCR7_64BYTE,
+		.rxtrig_bytes	= {1, 16, 32, 56},
 		.flags		= UART_CAP_FIFO | UART_CAP_SLEEP | UART_CAP_AFE,
 	},
 	[PORT_STARTECH] = {

@@ -209,6 +211,7 @@ static const struct serial8250_config uart_config[] = {
 		.tx_loadsz	= 32,
 		.fcr		= UART_FCR_ENABLE_FIFO | UART_FCR_R_TRIG_01 |
 				  UART_FCR_T_TRIG_10,
+		.rxtrig_bytes	= {8, 16, 56, 60},
 		.flags		= UART_CAP_FIFO | UART_CAP_EFR | UART_CAP_SLEEP,
 	},
 	[PORT_16850] = {

@@ -266,6 +269,7 @@ static const struct serial8250_config uart_config[] = {
 		.tx_loadsz	= 8,
 		.fcr		= UART_FCR_ENABLE_FIFO | UART_FCR_R_TRIG_01 |
 				  UART_FCR_T_TRIG_01,
+		.rxtrig_bytes	= {1, 4, 8, 14},
 		.flags		= UART_CAP_FIFO | UART_CAP_RTOIE,
 	},
 	[PORT_XR17D15X] = {

@@ -531,11 +535,8 @@ 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);
+	serial_out(p, UART_FCR, p->fcr);
 }
 EXPORT_SYMBOL_GPL(serial8250_clear_and_reinit_fifos);
 

@@ -2275,10 +2276,9 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
 {
 	struct uart_8250_port *up =
 		container_of(port, struct uart_8250_port, port);
-	unsigned char cval, fcr = 0;
+	unsigned char cval;
 	unsigned long flags;
 	unsigned int baud, quot;
-	int fifo_bug = 0;
 
 	switch (termios->c_cflag & CSIZE) {
 	case CS5:

@@ -2301,7 +2301,7 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
 	if (termios->c_cflag & PARENB) {
 		cval |= UART_LCR_PARITY;
 		if (up->bugs & UART_BUG_PARITY)
-			fifo_bug = 1;
+			up->fifo_bug = true;
 	}
 	if (!(termios->c_cflag & PARODD))
 		cval |= UART_LCR_EPAR;

@@ -2325,10 +2325,10 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
 		quot++;
 
 	if (up->capabilities & UART_CAP_FIFO && port->fifosize > 1) {
-		fcr = uart_config[port->type].fcr;
-		if ((baud < 2400 && !up->dma) || fifo_bug) {
-			fcr &= ~UART_FCR_TRIGGER_MASK;
-			fcr |= UART_FCR_TRIGGER_1;
+		/* NOTE: If fifo_bug is not set, a user can set RX_trigger. */
+		if ((baud < 2400 && !up->dma) || up->fifo_bug) {
+			up->fcr &= ~UART_FCR_TRIGGER_MASK;
+			up->fcr |= UART_FCR_TRIGGER_1;
 		}
 	}
 

@@ -2459,15 +2459,15 @@ 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);

@@ -2660,6 +2660,146 @@ static int serial8250_request_port(struct uart_port *port)
 	return ret;
 }
 
+static int fcr_get_rxtrig_bytes(struct uart_8250_port *up)
+{
+	const struct serial8250_config *conf_type = &uart_config[up->port.type];
+	unsigned char bytes;
+
+	bytes = conf_type->rxtrig_bytes[UART_FCR_R_TRIG_BITS(up->fcr)];
+
+	return bytes ? bytes : -EOPNOTSUPP;
+}
+
+static int bytes_to_fcr_rxtrig(struct uart_8250_port *up, unsigned char bytes)
+{
+	const struct serial8250_config *conf_type = &uart_config[up->port.type];
+	int i;
+
+	if (!conf_type->rxtrig_bytes[UART_FCR_R_TRIG_BITS(UART_FCR_R_TRIG_00)])
+		return -EOPNOTSUPP;
+
+	for (i = 1; i < UART_FCR_R_TRIG_MAX_STATE; i++) {
+		if (bytes < conf_type->rxtrig_bytes[i])
+			/* Use the nearest lower value */
+			return (--i) << UART_FCR_R_TRIG_SHIFT;
+	}
+
+	return UART_FCR_R_TRIG_11;
+}
+
+static int do_get_rxtrig(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 -EINVAL;
+
+	return fcr_get_rxtrig_bytes(up);
+}
+
+static int do_serial8250_get_rxtrig(struct tty_port *port)
+{
+	int rxtrig_bytes;
+
+	mutex_lock(&port->mutex);
+	rxtrig_bytes = do_get_rxtrig(port);
+	mutex_unlock(&port->mutex);
+
+	return rxtrig_bytes;
+}
+
+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);
+	int rxtrig_bytes;
+
+	rxtrig_bytes = do_serial8250_get_rxtrig(port);
+	if (rxtrig_bytes < 0)
+		return rxtrig_bytes;
+
+	return snprintf(buf, PAGE_SIZE, "%d\n", rxtrig_bytes);
+}
+
+static int do_set_rxtrig(struct tty_port *port, unsigned char bytes)
+{
+	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);
+	int rxtrig;
+
+	if (!(up->capabilities & UART_CAP_FIFO) || uport->fifosize <= 1 ||
+	    up->fifo_bug)
+		return -EINVAL;
+
+	rxtrig = bytes_to_fcr_rxtrig(up, bytes);
+	if (rxtrig < 0)
+		return rxtrig;
+
+	serial8250_clear_fifos(up);
+	up->fcr &= ~UART_FCR_TRIGGER_MASK;
+	up->fcr |= (unsigned char)rxtrig;
+	serial_out(up, UART_FCR, up->fcr);
+	return 0;
+}
+
+static int do_serial8250_set_rxtrig(struct tty_port *port, unsigned char bytes)
+{
+	int ret;
+
+	mutex_lock(&port->mutex);
+	ret = do_set_rxtrig(port, bytes);
+	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 bytes;
+	int ret;
+
+	if (!count)
+		return -EINVAL;
+
+	ret = kstrtou8(buf, 10, &bytes);
+	if (ret < 0)
+		return ret;
+
+	ret = do_serial8250_set_rxtrig(port, bytes);

drivers/tty/serial/8250/8250_core.c +12 -0

+
+static void register_dev_spec_attr_grp(struct uart_8250_port *up)
+{
+	const struct serial8250_config *conf_type = &uart_config[up->port.type];
+
+	if (conf_type->rxtrig_bytes[0])
+		up->port.dev_spec_attr_group = &serial8250_dev_attr_group;
+}
+
 static void serial8250_config_port(struct uart_port *port, int flags)
 {
 	struct uart_8250_port *up =

@@ -2708,6 +2848,9 @@ 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);
+	up->fcr = uart_config[up->port.type].fcr;
 }
 
 static int

drivers/tty/serial/serial_core.c +7 -6

index 2cf5649..41ac44b 100644
@@ -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);
 

On Thu, Apr 17, 2014 at 03:06:44PM +0900, Yoshihiro YUNOMAE wrote:

drivers/tty/serial/8250/8250_core.c static int serial8250_request_port(struct uart_port *port) · line 2785

Quoted 4 lines

drivers/tty/serial/8250/8250_core.c +4 -0

+static DEVICE_ATTR(rx_int_trig, S_IRUSR | S_IWUSR | S_IRGRP,
+		   serial8250_get_attr_rx_int_trig,
+		   serial8250_set_attr_rx_int_trig);
+

As you are adding a new sysfs attribute, you have to add a Documentation/ABI/ entry as well.

drivers/tty/serial/8250/8250_core.c static int serial8250_request_port(struct uart_port *port) · line 2793

Quoted 8 lines

drivers/tty/serial/8250/8250_core.c +8 -0

+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,
+	};

What's wrong with the macro to create a group?

Quoted 53 lines

drivers/tty/serial/8250/8250_core.c +12 -0

+
+static void register_dev_spec_attr_grp(struct uart_8250_port *up)
+{
+	const struct serial8250_config *conf_type = &uart_config[up->port.type];
+
+	if (conf_type->rxtrig_bytes[0])
+		up->port.dev_spec_attr_group = &serial8250_dev_attr_group;
+}
+
  static void serial8250_config_port(struct uart_port *port, int flags)
  {
  	struct uart_8250_port *up =

@@ -2708,6 +2848,9 @@ 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);
+	up->fcr = uart_config[up->port.type].fcr;
  }
 
  static int

drivers/tty/serial/serial_core.c +7 -6

index 2cf5649..41ac44b 100644
@@ -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);
 

drivers/tty/serial/serial_core.c int uart_add_one_port(struct uart_driver *drv, struct uart_port *uport) · line 2619

Quoted 10 lines

drivers/tty/serial/serial_core.c +4 -1

+	make_uport_attr_grps(uport);
+
  	/*
  	 * Register the port whether it's detected or not.  This allows
  	 * setserial to be used to alter this port's 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 you have to cast that hard, something is wrong here, why are you doing that?

Hi Greg,

Thank you for your review.

Quoted 1 line · Greg Kroah-Hartman

On Thu, Apr 17, 2014 at 03:06:44PM +0900, Yoshihiro YUNOMAE wrote:

[snip]

Quoted 7 lines

drivers/tty/serial/8250/8250_core.c static int serial8250_request_port(struct uart_port *port) · line 2785

Quoted 4 lines

drivers/tty/serial/8250/8250_core.c +4 -0

+static DEVICE_ATTR(rx_int_trig, S_IRUSR | S_IWUSR | S_IRGRP,
+		   serial8250_get_attr_rx_int_trig,
+		   serial8250_set_attr_rx_int_trig);
+

As you are adding a new sysfs attribute, you have to add a Documentation/ABI/ entry as well.

I added this attribute to /sys/dev/char/*

, so the documentation may be sysfs-dev. However, any other attributes are not written at all. Should I add this description to it or is there another file?

Quoted 10 lines

drivers/tty/serial/8250/8250_core.c static int serial8250_request_port(struct uart_port *port) · line 2793

Quoted 8 lines

drivers/tty/serial/8250/8250_core.c +8 -0

+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,
+	};

What's wrong with the macro to create a group?

I'll explain about this below.

Quoted 53 lines

Quoted 53 lines

drivers/tty/serial/8250/8250_core.c +12 -0

+
+static void register_dev_spec_attr_grp(struct uart_8250_port *up)
+{
+	const struct serial8250_config *conf_type = &uart_config[up->port.type];
+
+	if (conf_type->rxtrig_bytes[0])
+		up->port.dev_spec_attr_group = &serial8250_dev_attr_group;
+}
+
 static void serial8250_config_port(struct uart_port *port, int flags)
 {
 	struct uart_8250_port *up =

@@ -2708,6 +2848,9 @@ 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);
+	up->fcr = uart_config[up->port.type].fcr;
 }
 
 static int

drivers/tty/serial/serial_core.c +7 -6

index 2cf5649..41ac44b 100644
@@ -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);
 

Quoted 13 lines

drivers/tty/serial/serial_core.c int uart_add_one_port(struct uart_driver *drv, struct uart_port *uport) · line 2619

Quoted 10 lines

drivers/tty/serial/serial_core.c +4 -1

+	make_uport_attr_grps(uport);
+
 	/*
 	 * Register the port whether it's detected or not.  This allows
 	 * setserial to be used to alter this port's 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 you have to cast that hard, something is wrong here, why are you doing that?

The attribute group in serial layer was defined as constant because serial layer has only common sysfs I/F. However, I want to change sysfs I/F for specific devices. So, I deleted 'const' from the definition of the attribute group in serial layer in order to make the attribute group be changeable. On the other hand, to pass the attribute group to tty layer, the group must be const because the 5th variable of tty_port_register_device_attr() is an attribute group with 'const', so I implemented like this. Although I investigated again, tty_port_register_device_attr() is used only here, and tty_register_device_attr() called by the function is called from 2 locations (the one of them passes NULL in the 5th variable). Therefore, we can delete 'const' for those functions, I think. How do you think about this?

Quoted 15 lines · Yoshihiro YUNOMAE

Hi Greg,

Thank you for your review.

Quoted 1 line · Greg Kroah-Hartman

On Thu, Apr 17, 2014 at 03:06:44PM +0900, Yoshihiro YUNOMAE wrote:

[snip]

Quoted 7 lines

drivers/tty/serial/8250/8250_core.c static int serial8250_request_port(struct uart_port *port) · line 2785

Quoted 4 lines

drivers/tty/serial/8250/8250_core.c +4 -0

+static DEVICE_ATTR(rx_int_trig, S_IRUSR | S_IWUSR | S_IRGRP,
+		   serial8250_get_attr_rx_int_trig,
+		   serial8250_set_attr_rx_int_trig);
+

As you are adding a new sysfs attribute, you have to add a Documentation/ABI/ entry as well.

Quoted 1 line

I added this attribute to /sys/dev/char/*

What? No. That's not ok, why would it be?

See, Documentation would have pointed that problem out very obviously :)

Quoted 3 lines

, so the documentation may be sysfs-dev. However, any other attributes are not written at all. Should I add this description to it or is there another file?

It shouldn't be on a char device, that's not acceptable.

Quoted 80 lines

Quoted 10 lines

drivers/tty/serial/8250/8250_core.c static int serial8250_request_port(struct uart_port *port) · line 2793

Quoted 8 lines

drivers/tty/serial/8250/8250_core.c +8 -0

+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,
+	};

What's wrong with the macro to create a group?

I'll explain about this below.

Quoted 53 lines

Quoted 53 lines

drivers/tty/serial/8250/8250_core.c +12 -0

+
+static void register_dev_spec_attr_grp(struct uart_8250_port *up)
+{
+	const struct serial8250_config *conf_type = &uart_config[up->port.type];
+
+	if (conf_type->rxtrig_bytes[0])
+		up->port.dev_spec_attr_group = &serial8250_dev_attr_group;
+}
+
  static void serial8250_config_port(struct uart_port *port, int flags)
  {
  	struct uart_8250_port *up =

@@ -2708,6 +2848,9 @@ 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);
+	up->fcr = uart_config[up->port.type].fcr;
  }
 
  static int

drivers/tty/serial/serial_core.c +7 -6

index 2cf5649..41ac44b 100644
@@ -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);
 

Quoted 13 lines

drivers/tty/serial/serial_core.c int uart_add_one_port(struct uart_driver *drv, struct uart_port *uport) · line 2619

Quoted 10 lines

drivers/tty/serial/serial_core.c +4 -1

+	make_uport_attr_grps(uport);
+
  	/*
  	 * Register the port whether it's detected or not.  This allows
  	 * setserial to be used to alter this port's 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 you have to cast that hard, something is wrong here, why are you doing that?

Quoted 13 lines

The attribute group in serial layer was defined as constant because serial layer has only common sysfs I/F. However, I want to change sysfs I/F for specific devices. So, I deleted 'const' from the definition of the attribute group in serial layer in order to make the attribute group be changeable. On the other hand, to pass the attribute group to tty layer, the group must be const because the 5th variable of tty_port_register_device_attr() is an attribute group with 'const', so I implemented like this. Although I investigated again, tty_port_register_device_attr() is used only here, and tty_register_device_attr() called by the function is called from 2 locations (the one of them passes NULL in the 5th variable). Therefore, we can delete 'const' for those functions, I think. How do you think about this?

I think you need to not be messing with the devices in /sys/dev/char/ at all...

And why do you feel you need a sysfs attribute at all? What is it going to be used for? Who needs it? Without knowing that, I can't really answer your questions...