/dev/spidevB.C interface

Add a filesystem API for <linux/spi/spi.h> stack.  The initial version of
this interface is purely synchronous.

dbrownell@users.sourceforge.net:

 Cleaned up, bugfixed; much simplified; added preliminary documentation.

 Works with mdev given CONFIG_SYSFS_DEPRECATED; and presumably udev.

 Updated SPI_IOC_MESSAGE ioctl to full spi_message semantics, supporting
 groups of one or more transfers (each of which may be full duplex if
 desired).

 This is marked as EXPERIMENTAL with an explicit disclaimer that the API
 (notably the ioctls) is subject to change.
Signed-off-by: Andrea Paterniani <a.paterniani@swapp-eng.it>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/spi/spidev

+SPI devices have a limited userspace API, supporting basic half-duplex
+read() and write() access to SPI slave devices.  Using ioctl() requests,
+full duplex transfers and device I/O configuration are also available.
+
+	#include <fcntl.h>
+	#include <unistd.h>
+	#include <sys/ioctl.h>
+	#include <linux/types.h>
+	#include <linux/spi/spidev.h>
+
+Some reasons you might want to use this programming interface include:
+
+ * Prototyping in an environment that's not crash-prone; stray pointers
+   in userspace won't normally bring down any Linux system.
+
+ * Developing simple protocols used to talk to microcontrollers acting
+   as SPI slaves, which you may need to change quite often.
+
+Of course there are drivers that can never be written in userspace, because
+they need to access kernel interfaces (such as IRQ handlers or other layers
+of the driver stack) that are not accessible to userspace.
+
+
+DEVICE CREATION, DRIVER BINDING
+===============================
+The simplest way to arrange to use this driver is to just list it in the
+spi_board_info for a device as the driver it should use:  the "modalias"
+entry is "spidev", matching the name of the driver exposing this API.
+Set up the other device characteristics (bits per word, SPI clocking,
+chipselect polarity, etc) as usual, so you won't always need to override
+them later.
+
+(Sysfs also supports userspace driven binding/unbinding of drivers to
+devices.  That mechanism might be supported here in the future.)
+
+When you do that, the sysfs node for the SPI device will include a child
+device node with a "dev" attribute that will be understood by udev or mdev.
+(Larger systems will have "udev".  Smaller ones may configure "mdev" into
+busybox; it's less featureful, but often enough.)  For a SPI device with
+chipselect C on bus B, you should see:
+
+    /dev/spidevB.C ... character special device, major number 153 with
+	a dynamically chosen minor device number.  This is the node
+	that userspace programs will open, created by "udev" or "mdev".
+
+    /sys/devices/.../spiB.C ... as usual, the SPI device node will
+	be a child of its SPI master controller.
+
+    /sys/class/spidev/spidevB.C ... created when the "spidev" driver
+	binds to that device.  (Directory or symlink, based on whether
+	or not you enabled the "deprecated sysfs files" Kconfig option.)
+
+Do not try to manage the /dev character device special file nodes by hand.
+That's error prone, and you'd need to pay careful attention to system
+security issues; udev/mdev should already be configured securely.
+
+If you unbind the "spidev" driver from that device, those two "spidev" nodes
+(in sysfs and in /dev) should automatically be removed (respectively by the
+kernel and by udev/mdev).  You can unbind by removing the "spidev" driver
+module, which will affect all devices using this driver.  You can also unbind
+by having kernel code remove the SPI device, probably by removing the driver
+for its SPI controller (so its spi_master vanishes).
+
+Since this is a standard Linux device driver -- even though it just happens
+to expose a low level API to userspace -- it can be associated with any number
+of devices at a time.  Just provide one spi_board_info record for each such
+SPI device, and you'll get a /dev device node for each device.
+
+
+BASIC CHARACTER DEVICE API
+==========================
+Normal open() and close() operations on /dev/spidevB.D files work as you
+would expect.
+
+Standard read() and write() operations are obviously only half-duplex, and
+the chipselect is deactivated between those operations.  Full-duplex access,
+and composite operation without chipselect de-activation, is available using
+the SPI_IOC_MESSAGE(N) request.
+
+Several ioctl() requests let your driver read or override the device's current
+settings for data transfer parameters:
+
+    SPI_IOC_RD_MODE, SPI_IOC_WR_MODE ... pass a pointer to a byte which will
+	return (RD) or assign (WR) the SPI transfer mode.  Use the constants
+	SPI_MODE_0..SPI_MODE_3; or if you prefer you can combine SPI_CPOL
+	(clock polarity, idle high iff this is set) or SPI_CPHA (clock phase,
+	sample on trailing edge iff this is set) flags.
+
+    SPI_IOC_RD_LSB_FIRST, SPI_IOC_WR_LSB_FIRST ... pass a pointer to a byte
+	which will return (RD) or assign (WR) the bit justification used to
+	transfer SPI words.  Zero indicates MSB-first; other values indicate
+	the less common LSB-first encoding.  In both cases the specified value
+	is right-justified in each word, so that unused (TX) or undefined (RX)
+	bits are in the MSBs.
+
+    SPI_IOC_RD_BITS_PER_WORD, SPI_IOC_WR_BITS_PER_WORD ... pass a pointer to
+	a byte which will return (RD) or assign (WR) the number of bits in
+	each SPI transfer word.  The value zero signifies eight bits.
+
+    SPI_IOC_RD_MAX_SPEED_HZ, SPI_IOC_WR_MAX_SPEED_HZ ... pass a pointer to a
+	u32 which will return (RD) or assign (WR) the maximum SPI transfer
+	speed, in Hz.  The controller can't necessarily assign that specific
+	clock speed.
+
+NOTES:
+
+    - At this time there is no async I/O support; everything is purely
+      synchronous.
+
+    - There's currently no way to report the actual bit rate used to
+      shift data to/from a given device.
+
+    - From userspace, you can't currently change the chip select polarity;
+      that could corrupt transfers to other devices sharing the SPI bus.
+      Each SPI device is deselected when it's not in active use, allowing
+      other drivers to talk to other devices.
+
+    - There's a limit on the number of bytes each I/O request can transfer
+      to the SPI device.  It defaults to one page, but that can be changed
+      using a module parameter.
+
+    - Because SPI has no low-level transfer acknowledgement, you usually
+      won't see any I/O errors when talking to a non-existent device.
+
+
+FULL DUPLEX CHARACTER DEVICE API
+================================
+
+See the sample program below for one example showing the use of the full
+duplex programming interface.  (Although it doesn't perform a full duplex
+transfer.)  The model is the same as that used in the kernel spi_sync()
+request; the individual transfers offer the same capabilities as are
+available to kernel drivers (except that it's not asynchronous).
+
+The example shows one half-duplex RPC-style request and response message.
+These requests commonly require that the chip not be deselected between
+the request and response.  Several such requests could be chained into
+a single kernel request, even allowing the chip to be deselected after
+each response.  (Other protocol options include changing the word size
+and bitrate for each transfer segment.)
+
+To make a full duplex request, provide both rx_buf and tx_buf for the
+same transfer.  It's even OK if those are the same buffer.
+
+
+SAMPLE PROGRAM
+==============
+
+--------------------------------	CUT HERE
+#include <stdio.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#include <string.h>
+
+#include <sys/ioctl.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+
+#include <linux/types.h>
+#include <linux/spi/spidev.h>
+
+
+static int verbose;
+
+static void do_read(int fd, int len)
+{
+	unsigned char	buf[32], *bp;
+	int		status;
+
+	/* read at least 2 bytes, no more than 32 */
+	if (len < 2)
+		len = 2;
+	else if (len > sizeof(buf))
+		len = sizeof(buf);
+	memset(buf, 0, sizeof buf);
+
+	status = read(fd, buf, len);
+	if (status < 0) {
+		perror("read");
+		return;
+	}
+	if (status != len) {
+		fprintf(stderr, "short read\n");
+		return;
+	}
+
+	printf("read(%2d, %2d): %02x %02x,", len, status,
+		buf[0], buf[1]);
+	status -= 2;
+	bp = buf + 2;
+	while (status-- > 0)
+		printf(" %02x", *bp++);
+	printf("\n");
+}
+
+static void do_msg(int fd, int len)
+{
+	struct spi_ioc_transfer	xfer[2];
+	unsigned char		buf[32], *bp;
+	int			status;
+
+	memset(xfer, 0, sizeof xfer);
+	memset(buf, 0, sizeof buf);
+
+	if (len > sizeof buf)
+		len = sizeof buf;
+
+	buf[0] = 0xaa;
+	xfer[0].tx_buf = (__u64) buf;
+	xfer[0].len = 1;
+
+	xfer[1].rx_buf = (__u64) buf;
+	xfer[1].len = len;
+
+	status = ioctl(fd, SPI_IOC_MESSAGE(2), xfer);
+	if (status < 0) {
+		perror("SPI_IOC_MESSAGE");
+		return;
+	}
+
+	printf("response(%2d, %2d): ", len, status);
+	for (bp = buf; len; len--)
+		printf(" %02x", *bp++);
+	printf("\n");
+}
+
+static void dumpstat(const char *name, int fd)
+{
+	__u8	mode, lsb, bits;
+	__u32	speed;
+
+	if (ioctl(fd, SPI_IOC_RD_MODE, &mode) < 0) {
+		perror("SPI rd_mode");
+		return;
+	}
+	if (ioctl(fd, SPI_IOC_RD_LSB_FIRST, &lsb) < 0) {
+		perror("SPI rd_lsb_fist");
+		return;
+	}
+	if (ioctl(fd, SPI_IOC_RD_BITS_PER_WORD, &bits) < 0) {
+		perror("SPI bits_per_word");
+		return;
+	}
+	if (ioctl(fd, SPI_IOC_RD_MAX_SPEED_HZ, &speed) < 0) {
+		perror("SPI max_speed_hz");
+		return;
+	}
+
+	printf("%s: spi mode %d, %d bits %sper word, %d Hz max\n",
+		name, mode, bits, lsb ? "(lsb first) " : "", speed);
+}
+
+int main(int argc, char **argv)
+{
+	int		c;
+	int		readcount = 0;
+	int		msglen = 0;
+	int		fd;
+	const char	*name;
+
+	while ((c = getopt(argc, argv, "hm:r:v")) != EOF) {
+		switch (c) {
+		case 'm':
+			msglen = atoi(optarg);
+			if (msglen < 0)
+				goto usage;
+			continue;
+		case 'r':
+			readcount = atoi(optarg);
+			if (readcount < 0)
+				goto usage;
+			continue;
+		case 'v':
+			verbose++;
+			continue;
+		case 'h':
+		case '?':
+usage:
+			fprintf(stderr,
+				"usage: %s [-h] [-m N] [-r N] /dev/spidevB.D\n",
+				argv[0]);
+			return 1;
+		}
+	}
+
+	if ((optind + 1) != argc)
+		goto usage;
+	name = argv[optind];
+
+	fd = open(name, O_RDWR);
+	if (fd < 0) {
+		perror("open");
+		return 1;
+	}
+
+	dumpstat(name, fd);
+
+	if (msglen)
+		do_msg(fd, msglen);
+
+	if (readcount)
+		do_read(fd, readcount);
+
+	close(fd);
+	return 0;
+}

drivers/spi/Kconfig

@@ -159,6 +159,15 @@ config SPI_AT25
 	  This driver can also be built as a module.  If so, the module
 	  will be called at25.
 
+config SPI_SPIDEV
+	tristate "User mode SPI device driver support"
+	depends on SPI_MASTER && EXPERIMENTAL
+	help
+	  This supports user mode SPI protocol drivers.
+
+	  Note that this application programming interface is EXPERIMENTAL
+	  and hence SUBJECT TO CHANGE WITHOUT NOTICE while it stabilizes.
+
 #
 # Add new SPI protocol masters in alphabetical order above this line
 #

drivers/spi/Makefile

@@ -25,6 +25,7 @@ obj-$(CONFIG_SPI_S3C24XX)		+= spi_s3c24xx.o
 
 # SPI protocol drivers (device/link on bus)
 obj-$(CONFIG_SPI_AT25)		+= at25.o
+obj-$(CONFIG_SPI_SPIDEV)	+= spidev.o
 # 	... add above this line ...
 
 # SPI slave controller drivers (upstream link)

include/linux/Kbuild

@@ -4,6 +4,7 @@ header-y += hdlc/
 header-y += isdn/
 header-y += nfsd/
 header-y += raid/
+header-y += spi/
 header-y += sunrpc/
 header-y += tc_act/
 header-y += netfilter/

include/linux/spi/Kbuild

+header-y += spidev.h

include/linux/spi/spidev.h

+/*
+ * include/linux/spi/spidev.h
+ *
+ * Copyright (C) 2006 SWAPP
+ *	Andrea Paterniani <a.paterniani@swapp-eng.it>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+  */
+
+#ifndef SPIDEV_H
+#define SPIDEV_H
+
+
+/* User space versions of kernel symbols for SPI clocking modes,
+ * matching <linux/spi/spi.h>
+ */
+
+#define SPI_CPHA		0x01
+#define SPI_CPOL		0x02
+
+#define SPI_MODE_0		(0|0)
+#define SPI_MODE_1		(0|SPI_CPHA)
+#define SPI_MODE_2		(SPI_CPOL|0)
+#define SPI_MODE_3		(SPI_CPOL|SPI_CPHA)
+
+
+/*---------------------------------------------------------------------------*/
+
+/* IOCTL commands */
+
+#define SPI_IOC_MAGIC			'k'
+
+/**
+ * struct spi_ioc_transfer - describes a single SPI transfer
+ * @tx_buf: Holds pointer to userspace buffer with transmit data, or null.
+ *	If no data is provided, zeroes are shifted out.
+ * @rx_buf: Holds pointer to userspace buffer for receive data, or null.
+ * @len: Length of tx and rx buffers, in bytes.
+ * @speed_hz: Temporary override of the device's bitrate.
+ * @bits_per_word: Temporary override of the device's wordsize.
+ * @delay_usecs: If nonzero, how long to delay after the last bit transfer
+ *	before optionally deselecting the device before the next transfer.
+ * @cs_change: True to deselect device before starting the next transfer.
+ *
+ * This structure is mapped directly to the kernel spi_transfer structure;
+ * the fields have the same meanings, except of course that the pointers
+ * are in a different address space (and may be of different sizes in some
+ * cases, such as 32-bit i386 userspace over a 64-bit x86_64 kernel).
+ * Zero-initialize the structure, including currently unused fields, to
+ * accomodate potential future updates.
+ *
+ * SPI_IOC_MESSAGE gives userspace the equivalent of kernel spi_sync().
+ * Pass it an array of related transfers, they'll execute together.
+ * Each transfer may be half duplex (either direction) or full duplex.
+ *
+ *	struct spi_ioc_transfer mesg[4];
+ *	...
+ *	status = ioctl(fd, SPI_IOC_MESSAGE(4), mesg);
+ *
+ * So for example one transfer might send a nine bit command (right aligned
+ * in a 16-bit word), the next could read a block of 8-bit data before
+ * terminating that command by temporarily deselecting the chip; the next
+ * could send a different nine bit command (re-selecting the chip), and the
+ * last transfer might write some register values.
+ */
+struct spi_ioc_transfer {
+	__u64		tx_buf;
+	__u64		rx_buf;
+
+	__u32		len;
+	__u32		speed_hz;
+
+	__u16		delay_usecs;
+	__u8		bits_per_word;
+	__u8		cs_change;
+	__u32		pad;
+
+	/* If the contents of 'struct spi_ioc_transfer' ever change
+	 * incompatibly, then the ioctl number (currently 0) must change;
+	 * ioctls with constant size fields get a bit more in the way of
+	 * error checking than ones (like this) where that field varies.
+	 *
+	 * NOTE: struct layout is the same in 64bit and 32bit userspace.
+	 */
+};
+
+/* not all platforms use <asm-generic/ioctl.h> or _IOC_TYPECHECK() ... */
+#define SPI_MSGSIZE(N) \
+	((((N)*(sizeof (struct spi_ioc_transfer))) < (1 << _IOC_SIZEBITS)) \
+		? ((N)*(sizeof (struct spi_ioc_transfer))) : 0)
+#define SPI_IOC_MESSAGE(N) _IOW(SPI_IOC_MAGIC, 0, char[SPI_MSGSIZE(N)])
+
+
+/* Read / Write of SPI mode (SPI_MODE_0..SPI_MODE_3) */
+#define SPI_IOC_RD_MODE			_IOR(SPI_IOC_MAGIC, 1, __u8)
+#define SPI_IOC_WR_MODE			_IOW(SPI_IOC_MAGIC, 1, __u8)
+
+/* Read / Write SPI bit justification */
+#define SPI_IOC_RD_LSB_FIRST		_IOR(SPI_IOC_MAGIC, 2, __u8)
+#define SPI_IOC_WR_LSB_FIRST		_IOW(SPI_IOC_MAGIC, 2, __u8)
+
+/* Read / Write SPI device word length (1..N) */
+#define SPI_IOC_RD_BITS_PER_WORD	_IOR(SPI_IOC_MAGIC, 3, __u8)
+#define SPI_IOC_WR_BITS_PER_WORD	_IOW(SPI_IOC_MAGIC, 3, __u8)
+
+/* Read / Write SPI device default max speed hz */
+#define SPI_IOC_RD_MAX_SPEED_HZ		_IOR(SPI_IOC_MAGIC, 4, __u32)
+#define SPI_IOC_WR_MAX_SPEED_HZ		_IOW(SPI_IOC_MAGIC, 4, __u32)
+
+
+
+#endif /* SPIDEV_H */