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

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Message-ID: <20080818162526.1975dace@lxorguk.ukuu.org.uk>
Date:	Mon, 18 Aug 2008 16:25:26 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	"Tosoni" <jp.tosoni@...sys.fr>
Cc:	"'Laurent Pinchart'" <laurentp@...-semaphore.com>,
	"'Aristeu Rozanski'" <arozansk@...hat.com>,
	<linux-serial@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] 8250: add support for DTR/DSR hardware flow control

On Thu, 7 Aug 2008 14:54:05 +0200
"Tosoni" <jp.tosoni@...sys.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@...hat.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@...hat.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>
--
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