[PATCH v1] 8250: add support for DTR/DSR hardware flow control

[PATCH v1] 8250: add support for DTR/DSR hardware flow control

[Aristeu Rozanski]

This patch adds support for DTR/DSR hardware flow control on 8250 driver on x86
machines. It's done by adding a CDTRDSR flag to work just like CRTSCTS, which is
not done on other architectures on purpose (so each maintainer can allocate it).

This patch was tested with success with a serial printer configured with a small
buffer and DTR/DSR flow control.

This is based on the work of Michael Westermann (http://lkml.org/lkml/2007/8/31/133)

Comments more than welcome.

Signed-off-by: Aristeu Rozanski <arozansk@redhat.com>

---
 drivers/serial/8250.c        |   12 ++++++++--
 drivers/serial/serial_core.c |   42 ++++++++++++++++++++++++++++++++++-
 include/asm-x86/termbits.h   |    1 
 include/linux/serial_core.h  |   51 +++++++++++++++++++++++++++----------------
 include/linux/termios.h      |    5 ++++
 5 files changed, 90 insertions(+), 21 deletions(-)

--- linus-2.6.orig/drivers/serial/8250.c	2008-08-05 16:44:26.000000000 -0400
+++ linus-2.6/drivers/serial/8250.c	2008-08-05 18:45:01.000000000 -0400
@@ -1409,7 +1409,7 @@ static unsigned int check_modem_status(s
 		if (status & UART_MSR_TERI)
 			up->port.icount.rng++;
 		if (status & UART_MSR_DDSR)
-			up->port.icount.dsr++;
+			uart_handle_dsr_change(&up->port, status & UART_MSR_DSR);
 		if (status & UART_MSR_DDCD)
 			uart_handle_dcd_change(&up->port, status & UART_MSR_DCD);
 		if (status & UART_MSR_DCTS)
@@ -1739,9 +1739,17 @@ static inline void wait_for_xmitr(struct
 		unsigned int tmout;
 		for (tmout = 1000000; tmout; tmout--) {
 			unsigned int msr = serial_in(up, UART_MSR);
+			struct uart_info *info = up->port.info;
+
 			up->msr_saved_flags |= msr & MSR_SAVE_FLAGS;
-			if (msr & UART_MSR_CTS)
+
+			if ((info->flags & UIF_CTS_FLOW) &&
+			    (msr & UART_MSR_CTS))
 				break;
+			else if ((info->flags & UIF_DSR_FLOW) &&
+				 (msr & UART_MSR_DSR))
+ 				break;
+
 			udelay(1);
 			touch_nmi_watchdog();
 		}
--- linus-2.6.orig/drivers/serial/serial_core.c	2008-08-05 16:44:26.000000000 -0400
+++ linus-2.6/drivers/serial/serial_core.c	2008-08-05 18:45:01.000000000 -0400
@@ -194,6 +194,13 @@ static int uart_startup(struct uart_stat
 			spin_unlock_irq(&port->lock);
 		}
 
+		if (info->flags & UIF_DSR_FLOW) {
+			spin_lock_irq(&port->lock);
+			if (!(port->ops->get_mctrl(port) & TIOCM_DSR))
+				info->port.tty->hw_stopped = 1;
+			spin_unlock_irq(&port->lock);
+		}
+
 		info->flags |= UIF_INITIALIZED;
 
 		clear_bit(TTY_IO_ERROR, &info->port.tty->flags);
@@ -448,6 +455,11 @@ uart_change_speed(struct uart_state *sta
 	else
 		state->info->flags &= ~UIF_CTS_FLOW;
 
+	if (termios->c_cflag & CDTRDSR)
+		state->info->flags |= UIF_DSR_FLOW;
+	else
+		state->info->flags &= ~UIF_DSR_FLOW;
+
 	if (termios->c_cflag & CLOCAL)
 		state->info->flags &= ~UIF_CHECK_CD;
 	else
@@ -611,6 +623,8 @@ static void uart_throttle(struct tty_str
 
 	if (tty->termios->c_cflag & CRTSCTS)
 		uart_clear_mctrl(state->port, TIOCM_RTS);
+	if (tty->termios->c_cflag & CDTRDSR)
+		uart_clear_mctrl(state->port, TIOCM_DTR);
 }
 
 static void uart_unthrottle(struct tty_struct *tty)
@@ -627,6 +641,8 @@ static void uart_unthrottle(struct tty_s
 
 	if (tty->termios->c_cflag & CRTSCTS)
 		uart_set_mctrl(port, TIOCM_RTS);
+	if (tty->termios->c_cflag & CDTRDSR)
+		uart_set_mctrl(port, TIOCM_DTR);
 }
 
 static int uart_get_info(struct uart_state *state,
@@ -1212,6 +1228,9 @@ static void uart_set_termios(struct tty_
 		if (!(cflag & CRTSCTS) ||
 		    !test_bit(TTY_THROTTLED, &tty->flags))
 			mask |= TIOCM_RTS;
+		if (!(cflag & CDTRDSR) ||
+		    !test_bit(TTY_THROTTLED, &tty->flags))
+			mask &= ~TIOCM_DTR;
 		uart_set_mctrl(state->port, mask);
 	}
 
@@ -1232,6 +1251,24 @@ static void uart_set_termios(struct tty_
 		}
 		spin_unlock_irqrestore(&state->port->lock, flags);
 	}
+
+	/* Handle turning off CDTRDSR */
+	if ((old_termios->c_cflag & CDTRDSR) && !(cflag & CDTRDSR)) {
+		spin_lock_irqsave(&state->port->lock, flags);
+		tty->hw_stopped = 0;
+		__uart_start(tty);
+		spin_unlock_irqrestore(&state->port->lock, flags);
+	}
+
+	if (!(old_termios->c_cflag & CDTRDSR) && (cflag & CDTRDSR)) {
+		spin_lock_irqsave(&state->port->lock, flags);
+		if (!(state->port->ops->get_mctrl(state->port) & TIOCM_DSR)) {
+			tty->hw_stopped = 1;
+			state->port->ops->stop_tx(state->port);
+		}
+		spin_unlock_irqrestore(&state->port->lock, flags);
+	}
+
 #if 0
 	/*
 	 * No need to wake up processes in open wait, since they
@@ -1511,7 +1548,8 @@ uart_block_til_ready(struct file *filp, 
 		 * not set RTS here - we want to make sure we catch
 		 * the data from the modem.
 		 */
-		if (info->port.tty->termios->c_cflag & CBAUD)
+		if (info->port.tty->termios->c_cflag & CBAUD &&
+		    !(info->port.tty->termios->c_cflag & CDTRDSR))
 			uart_set_mctrl(port, TIOCM_DTR);
 
 		/*
@@ -1959,6 +1997,8 @@ uart_set_options(struct uart_port *port,
 
 	if (flow == 'r')
 		termios.c_cflag |= CRTSCTS;
+	if (flow == 'd')
+		termios.c_cflag |= CDTRDSR;
 
 	/*
 	 * some uarts on other side don't support no flow control.
--- linus-2.6.orig/include/asm-x86/termbits.h	2008-08-05 16:44:26.000000000 -0400
+++ linus-2.6/include/asm-x86/termbits.h	2008-08-06 13:33:57.000000000 -0400
@@ -157,6 +157,7 @@ struct ktermios {
 #define  B3500000 0010016
 #define  B4000000 0010017
 #define CIBAUD	  002003600000	/* input baud rate */
+#define CDTRDSR	  004000000000	/* DTR/DSR flow control */
 #define CMSPAR	  010000000000	/* mark or space (stick) parity */
 #define CRTSCTS	  020000000000	/* flow control */
 
--- linus-2.6.orig/include/linux/serial_core.h	2008-08-05 16:44:26.000000000 -0400
+++ linus-2.6/include/linux/serial_core.h	2008-08-05 18:45:01.000000000 -0400
@@ -351,6 +351,7 @@ struct uart_info {
  *
  * FIXME: use the ASY_ definitions
  */
+#define UIF_DSR_FLOW		((__force uif_t) (1 << 24))
 #define UIF_CHECK_CD		((__force uif_t) (1 << 25))
 #define UIF_CTS_FLOW		((__force uif_t) (1 << 26))
 #define UIF_NORMAL_ACTIVE	((__force uif_t) (1 << 29))
@@ -505,34 +506,48 @@ uart_handle_dcd_change(struct uart_port 
 }
 
 /**
- *	uart_handle_cts_change - handle a change of clear-to-send state
+ *	uart_handle_flow_control_change - handle a change of CTS or DSR
  *	@port: uart_port structure for the open port
- *	@status: new clear to send status, nonzero if active
+ *	@status: new CTS/DTR status, nonzero if active
  */
 static inline void
-uart_handle_cts_change(struct uart_port *port, unsigned int status)
+uart_handle_flow_control_change(struct uart_port *port, unsigned int status)
 {
 	struct uart_info *info = port->info;
 	struct tty_struct *tty = info->port.tty;
 
-	port->icount.cts++;
-
-	if (info->flags & UIF_CTS_FLOW) {
-		if (tty->hw_stopped) {
-			if (status) {
-				tty->hw_stopped = 0;
-				port->ops->start_tx(port);
-				uart_write_wakeup(port);
-			}
-		} else {
-			if (!status) {
-				tty->hw_stopped = 1;
-				port->ops->stop_tx(port);
-			}
+	if (tty->hw_stopped) {
+		if (status) {
+			tty->hw_stopped = 0;
+			port->ops->start_tx(port);
+			uart_write_wakeup(port);
+		}
+	} else {
+		if (!status) {
+			tty->hw_stopped = 1;
+			port->ops->stop_tx(port);
 		}
 	}
 }
 
+static inline void
+uart_handle_cts_change(struct uart_port *port, unsigned int status)
+{
+	struct uart_info *info = port->info;
+	port->icount.cts++;
+	if (info->flags & UIF_CTS_FLOW)
+		uart_handle_flow_control_change(port, status);
+}
+
+static inline void
+uart_handle_dsr_change(struct uart_port *port, unsigned int status)
+{
+	struct uart_info *info = port->info;
+	port->icount.dsr++;
+	if (info->flags & UIF_DSR_FLOW)
+		uart_handle_flow_control_change(port, status);
+}
+
 #include <linux/tty_flip.h>
 
 static inline void
@@ -556,7 +571,7 @@ uart_insert_char(struct uart_port *port,
  *	UART_ENABLE_MS - determine if port should enable modem status irqs
  */
 #define UART_ENABLE_MS(port,cflag)	((port)->flags & UPF_HARDPPS_CD || \
-					 (cflag) & CRTSCTS || \
+					 (cflag) & (CRTSCTS | CDTRDSR) || \
 					 !((cflag) & CLOCAL))
 
 #endif
--- linus-2.6.orig/include/linux/termios.h	2008-08-05 16:44:26.000000000 -0400
+++ linus-2.6/include/linux/termios.h	2008-08-05 18:45:01.000000000 -0400
@@ -4,4 +4,9 @@
 #include <linux/types.h>
 #include <asm/termios.h>
 
+#ifndef CDTRDSR
+#warning This architecture should implement CDTRDSR
+#define CDTRDSR 0 /* remove this when all architectures have a definition */
+#endif
+
 #endif

Re: [PATCH v1] 8250: add support for DTR/DSR hardware flow control

[Laurent Pinchart]

[-- Attachment #1: Type: text/plain, Size: 1158 bytes --]

Hi,

On Wednesday 06 August 2008, Aristeu Rozanski wrote:
> This patch adds support for DTR/DSR hardware flow control on 8250 driver on
> x86 machines. It's done by adding a CDTRDSR flag to work just like CRTSCTS,
> which is not done on other architectures on purpose (so each maintainer can
> allocate it). 

It's funny, serial flow control hasn't been discussed for a long time, and you're the third person to start a flow control related thread on this mailing list in a few days.

> This patch was tested with success with a serial printer configured with a
> small buffer and DTR/DSR flow control.
> 
> This is based on the work of Michael Westermann
> (http://lkml.org/lkml/2007/8/31/133) 
> 
> Comments more than welcome.

Please read the '[PATCH/RFC] 8250: Auto RS485 direction control' thread for background information. In a nutshell we need more than just CTS/RTS and DTR/DSR, and we don't have enough c_cflags bits. We will probably have to create a new ioctl.

Best regards,

-- 
Laurent Pinchart
CSE Semaphore Belgium

Chaussee de Bruxelles, 732A
B-1410 Waterloo
Belgium

T +32 (2) 387 42 59
F +32 (2) 387 42 75

[-- Attachment #2: This is a digitally signed message part. --]
[-- Type: application/pgp-signature, Size: 197 bytes --]

Re: [PATCH v1] 8250: add support for DTR/DSR hardware flow control

[Alan Cox]

> Please read the '[PATCH/RFC] 8250: Auto RS485 direction control' thread for background information. In a nutshell we need more than just CTS/RTS and DTR/DSR, and we don't have enough c_cflags bits. We will probably have to create a new ioctl.

Maybe - fortunately the kernel and user termios structure are now
independent so we can extend ktermios easily enough.

RE: [PATCH v1] 8250: add support for DTR/DSR hardware flow control

[Tosoni]

[-- Attachment #1: Type: text/plain, Size: 1985 bytes --]

In my opinion, DSR/DTR is another (wrong) way to do RTS/CTS flow control, so
I would have it implemented in setserial as a modifier to the CRTSCTS flag.

About a RS485 ioctl: could you consider the attached files which are already
in the Linux kernel (in include/asm-cris).
They define a TIOCSERSETRS485 (ioctl.h), and the data structure (rs485.h)
with allows to specify timings. Sounds just like what we want ?

JP Tosoni

> -----Original Message-----
> From: linux-serial-owner@vger.kernel.org
> [mailto:linux-serial-owner@vger.kernel.org]On Behalf Of
> Laurent Pinchart
> Sent: Thursday, August 07, 2008 10:32 AM
> To: Aristeu Rozanski
> Cc: linux-serial@vger.kernel.org; linux-kernel@vger.kernel.org
> Subject: Re: [PATCH v1] 8250: add support for DTR/DSR hardware flow
> control
>
>
> Hi,
>
> On Wednesday 06 August 2008, Aristeu Rozanski wrote:
> > This patch adds support for DTR/DSR hardware flow control
> on 8250 driver on
> > x86 machines. It's done by adding a CDTRDSR flag to work
> just like CRTSCTS,
> > which is not done on other architectures on purpose (so
> each maintainer can
> > allocate it).
>
> It's funny, serial flow control hasn't been discussed for a
> long time, and you're the third person to start a flow
> control related thread on this mailing list in a few days.
>
> > This patch was tested with success with a serial printer
> configured with a
> > small buffer and DTR/DSR flow control.
> >
> > This is based on the work of Michael Westermann
> > (http://lkml.org/lkml/2007/8/31/133)
> >
> > Comments more than welcome.
>
> Please read the '[PATCH/RFC] 8250: Auto RS485 direction
> control' thread for background information. In a nutshell we
> need more than just CTS/RTS and DTR/DSR, and we don't have
> enough c_cflags bits. We will probably have to create a new ioctl.
>
> Best regards,
>
> --
> Laurent Pinchart
> CSE Semaphore Belgium
>
> Chaussee de Bruxelles, 732A
> B-1410 Waterloo
> Belgium
>
> T +32 (2) 387 42 59
> F +32 (2) 387 42 75
>

[-- Attachment #2: ioctls.h --]
[-- Type: text/plain, Size: 2955 bytes --]

#ifndef __ARCH_CRIS_IOCTLS_H__
#define __ARCH_CRIS_IOCTLS_H__

/* verbatim copy of asm-i386/ioctls.h */

#include <asm/ioctl.h>

/* 0x54 is just a magic number to make these relatively unique ('T') */

#define TCGETS		0x5401
#define TCSETS		0x5402
#define TCSETSW		0x5403
#define TCSETSF		0x5404
#define TCGETA		0x5405
#define TCSETA		0x5406
#define TCSETAW		0x5407
#define TCSETAF		0x5408
#define TCSBRK		0x5409
#define TCXONC		0x540A
#define TCFLSH		0x540B
#define TIOCEXCL	0x540C
#define TIOCNXCL	0x540D
#define TIOCSCTTY	0x540E
#define TIOCGPGRP	0x540F
#define TIOCSPGRP	0x5410
#define TIOCOUTQ	0x5411
#define TIOCSTI		0x5412
#define TIOCGWINSZ	0x5413
#define TIOCSWINSZ	0x5414
#define TIOCMGET	0x5415
#define TIOCMBIS	0x5416
#define TIOCMBIC	0x5417
#define TIOCMSET	0x5418
#define TIOCGSOFTCAR	0x5419
#define TIOCSSOFTCAR	0x541A
#define FIONREAD	0x541B
#define TIOCINQ		FIONREAD
#define TIOCLINUX	0x541C
#define TIOCCONS	0x541D
#define TIOCGSERIAL	0x541E
#define TIOCSSERIAL	0x541F
#define TIOCPKT		0x5420
#define FIONBIO		0x5421
#define TIOCNOTTY	0x5422
#define TIOCSETD	0x5423
#define TIOCGETD	0x5424
#define TCSBRKP		0x5425	/* Needed for POSIX tcsendbreak() */
#define TIOCSBRK	0x5427  /* BSD compatibility */
#define TIOCCBRK	0x5428  /* BSD compatibility */
#define TIOCGSID	0x5429  /* Return the session ID of FD */
#define TCGETS2		_IOR('T',0x2A, struct termios2)
#define TCSETS2		_IOW('T',0x2B, struct termios2)
#define TCSETSW2	_IOW('T',0x2C, struct termios2)
#define TCSETSF2	_IOW('T',0x2D, struct termios2)
#define TIOCGPTN	_IOR('T',0x30, unsigned int) /* Get Pty Number (of pty-mux device) */
#define TIOCSPTLCK	_IOW('T',0x31, int)  /* Lock/unlock Pty */

#define FIONCLEX	0x5450  /* these numbers need to be adjusted. */
#define FIOCLEX		0x5451
#define FIOASYNC	0x5452
#define TIOCSERCONFIG	0x5453
#define TIOCSERGWILD	0x5454
#define TIOCSERSWILD	0x5455
#define TIOCGLCKTRMIOS	0x5456
#define TIOCSLCKTRMIOS	0x5457
#define TIOCSERGSTRUCT	0x5458 /* For debugging only */
#define TIOCSERGETLSR   0x5459 /* Get line status register */
#define TIOCSERGETMULTI 0x545A /* Get multiport config  */
#define TIOCSERSETMULTI 0x545B /* Set multiport config */

#define TIOCMIWAIT	0x545C	/* wait for a change on serial input line(s) */
#define TIOCGICOUNT	0x545D	/* read serial port inline interrupt counts */
#define TIOCGHAYESESP   0x545E  /* Get Hayes ESP configuration */
#define TIOCSHAYESESP   0x545F  /* Set Hayes ESP configuration */
#define FIOQSIZE	0x5460

#define TIOCSERSETRS485 0x5461  /* enable rs-485 */
#define TIOCSERWRRS485  0x5462  /* write rs-485 */

/* Used for packet mode */
#define TIOCPKT_DATA		 0
#define TIOCPKT_FLUSHREAD	 1
#define TIOCPKT_FLUSHWRITE	 2
#define TIOCPKT_STOP		 4
#define TIOCPKT_START		 8
#define TIOCPKT_NOSTOP		16
#define TIOCPKT_DOSTOP		32

#define TIOCSER_TEMT    0x01	/* Transmitter physically empty */

#endif

[-- Attachment #3: rs485.h --]
[-- Type: text/plain, Size: 474 bytes --]

/* RS-485 structures */

/* RS-485 support */
/* Used with ioctl() TIOCSERSETRS485 */
struct rs485_control {
        unsigned short rts_on_send;
        unsigned short rts_after_sent;
        unsigned long delay_rts_before_send;
        unsigned short enabled;
#ifdef __KERNEL__
        int disable_serial_loopback;
#endif
};

/* Used with ioctl() TIOCSERWRRS485 */
struct rs485_write {
        unsigned short outc_size;
        unsigned char *outc;
};

Re: [PATCH v1] 8250: add support for DTR/DSR hardware flow control

[Alan Cox]

> About a RS485 ioctl: could you consider the attached files which are already
> in the Linux kernel (in include/asm-cris).
> They define a TIOCSERSETRS485 (ioctl.h), and the data structure (rs485.h)
> with allows to specify timings. Sounds just like what we want ?

That would make sense for hardware assisted RS485 but we still have to
sort out DTR/DSR as well

Re: [PATCH v1] 8250: add support for DTR/DSR hardware flow control

[Alan Cox]

On Thu, 7 Aug 2008 14:54:05 +0200
"Tosoni" <jp.tosoni@acksys.fr> wrote:

> About a RS485 ioctl: could you consider the attached files which are already
> in the Linux kernel (in include/asm-cris).
> They define a TIOCSERSETRS485 (ioctl.h), and the data structure (rs485.h)
> with allows to specify timings. Sounds just like what we want ?

I had a deeper look at this for RS485 and the answer is "sort of". I've
reworked the structure to keep it the same size irrespective of 32/64bit
systems, and to make stuff flags that can be, plus add some extra u32
words in case we need to (.. when we need to ;)) add stuff later.

Comments, thoughts - will this do what people in the RS485 world need ?

Alan
--------------

tty: Cris has a nice RS485 ioctl so we should steal it

From: Alan Cox <alan@redhat.com>

JP Tosoni observed:

"About a RS485 ioctl: could you consider the attached files which are
 already in the Linux kernel (in include/asm-cris).  They define a
 TIOCSERSETRS485 (ioctl.h), and the data structure (rs485.h)
 with allows to specify timings. Sounds just like what we want ?"

and he's right: sort of. Rework the structure to use flag bits and make the
time delay a fixed sized field so we don't get 32/64bit problems. Add the ioctls
to x86 so that people know what to add to their platform of choice.

Signed-off-by: Alan Cox <alan@redhat.com>
---

 include/asm-x86/ioctls.h |    2 ++
 include/linux/serial.h   |   16 ++++++++++++++++
 2 files changed, 18 insertions(+), 0 deletions(-)


diff --git a/include/asm-x86/ioctls.h b/include/asm-x86/ioctls.h
index c0c338b..2cd4775 100644
--- a/include/asm-x86/ioctls.h
+++ b/include/asm-x86/ioctls.h
@@ -51,6 +51,8 @@
 #define TCSETS2		_IOW('T', 0x2B, struct termios2)
 #define TCSETSW2	_IOW('T', 0x2C, struct termios2)
 #define TCSETSF2	_IOW('T', 0x2D, struct termios2)
+#define TIOCGRS485	0x542E
+#define TIOCSRS485	0x542F
 #define TIOCGPTN	_IOR('T', 0x30, unsigned int)
 				/* Get Pty Number (of pty-mux device) */
 #define TIOCSPTLCK	_IOW('T', 0x31, int)  /* Lock/unlock Pty */
diff --git a/include/linux/serial.h b/include/linux/serial.h
index deb7143..1ea8d92 100644
--- a/include/linux/serial.h
+++ b/include/linux/serial.h
@@ -173,6 +173,22 @@ struct serial_icounter_struct {
 	int reserved[9];
 };
 
+/*
+ * Serial interface for controlling RS485 settings on chips with suitable
+ * support. Set with TIOCSRS485 and get with TIOCGRS485 if supported by your
+ * platform. The set function returns the new state, with any unsupported bits
+ * reverted appropriately.
+ */
+
+struct serial_rs485 {
+	__u32	flags;			/* RS485 feature flags */
+#define SER_RS485_ENABLED		(1 << 0)
+#define SER_RS485_RTS_ON_SEND		(1 << 1)
+#define SER_RS485_RTS_AFTER_SEND	(1 << 2)
+	__u32	delay_rts_before_send;	/* Milliseconds */
+	__u32	padding[6];		/* Memory is cheap, new structs
+					   are a royal PITA .. */
+};
 
 #ifdef __KERNEL__
 #include <linux/compiler.h>

Re: [PATCH v1] 8250: add support for DTR/DSR hardware flow control

[Aristeu Rozanski]

> > About a RS485 ioctl: could you consider the attached files which are already
> > in the Linux kernel (in include/asm-cris).
> > They define a TIOCSERSETRS485 (ioctl.h), and the data structure (rs485.h)
> > with allows to specify timings. Sounds just like what we want ?
> 
> I had a deeper look at this for RS485 and the answer is "sort of". I've
> reworked the structure to keep it the same size irrespective of 32/64bit
> systems, and to make stuff flags that can be, plus add some extra u32
> words in case we need to (.. when we need to ;)) add stuff later.
> 
> Comments, thoughts - will this do what people in the RS485 world need ?
as for DTR/DSR patch, will be used the same approach?

-- 
Aristeu

Re: [PATCH v1] 8250: add support for DTR/DSR hardware flow control

[Alan Cox]

On Wed, 20 Aug 2008 17:43:36 -0400
Aristeu Rozanski <aris@ruivo.org> wrote:

> > > About a RS485 ioctl: could you consider the attached files which are already
> > > in the Linux kernel (in include/asm-cris).
> > > They define a TIOCSERSETRS485 (ioctl.h), and the data structure (rs485.h)
> > > with allows to specify timings. Sounds just like what we want ?
> > 
> > I had a deeper look at this for RS485 and the answer is "sort of". I've
> > reworked the structure to keep it the same size irrespective of 32/64bit
> > systems, and to make stuff flags that can be, plus add some extra u32
> > words in case we need to (.. when we need to ;)) add stuff later.
> > 
> > Comments, thoughts - will this do what people in the RS485 world need ?
> as for DTR/DSR patch, will be used the same approach?

I'm still trying to get a sensible answer on how other Unixes handle it

Re: [PATCH v1] 8250: add support for DTR/DSR hardware flow control

['Aristeu Rozanski']

> > > > About a RS485 ioctl: could you consider the attached files which are already
> > > > in the Linux kernel (in include/asm-cris).
> > > > They define a TIOCSERSETRS485 (ioctl.h), and the data structure (rs485.h)
> > > > with allows to specify timings. Sounds just like what we want ?
> > > 
> > > I had a deeper look at this for RS485 and the answer is "sort of". I've
> > > reworked the structure to keep it the same size irrespective of 32/64bit
> > > systems, and to make stuff flags that can be, plus add some extra u32
> > > words in case we need to (.. when we need to ;)) add stuff later.
> > > 
> > > Comments, thoughts - will this do what people in the RS485 world need ?
> > as for DTR/DSR patch, will be used the same approach?
> 
> I'm still trying to get a sensible answer on how other Unixes handle it
I did some research on that:
Solaris and AIX:
	TC{G,S}ETX for extended options and only input flow control (DTRXOFF)
SCO:
	{S,G}ETFLOW for configuring flow control, TXHARD, RXHARD for DTRDSR
FreeBSD:
	cflags has 'dtrflow' and 'dsrflow'

Having the option to set individually which pins to use for input and output
flow control and which ones should be on/off all the time seem to be a powerful
way to do it, instead of having a "CDTRDSR".

-- 
Aristeu