FMC: add a char-device mezzanine driver

This driver exports the memory area associated with the mezzanine card
as a misc device, so users can access registers.
Signed-off-by: Alessandro Rubini <rubini@gnudd.com>
Acked-by: Juan David Gonzalez Cobas <dcobas@cern.ch>
Acked-by: Emilio G. Cota <cota@braap.org>
Acked-by: Samuel Iglesias Gonsalvez <siglesias@igalia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/fmc/00-INDEX

@@ -33,3 +33,6 @@ fmc-trivial.txt
 
 fmc-write-eeprom.txt
 	- about drivers/fmc/fmc-write-eeprom.ko
+
+fmc-chardev.txt
+	- about drivers/fmc/fmc-chardev.ko

Documentation/fmc/fmc-chardev.txt

+fmc-chardev
+===========
+
+This is a simple generic driver, that allows user access by means of a
+character device (actually, one for each mezzanine it takes hold of).
+
+The char device is created as a misc device. Its name in /dev (as
+created by udev) is the same name as the underlying FMC device. Thus,
+the name can be a silly fmc-0000 look-alike if the device has no
+identifiers nor bus_id, a more specific fmc-0400 if the device has a
+bus-specific address but no associated name, or something like
+fdelay-0400 if the FMC core can rely on both a mezzanine name and a bus
+address.
+
+Currently the driver only supports read and write: you can lseek to the
+desired address and read or write a register.
+
+The driver assumes all registers are 32-bit in size, and only accepts a
+single read or write per system call. However, as a result of Unix read
+and write semantics, users can simply fread or fwrite bigger areas in
+order to dump or store bigger memory areas.
+
+There is currently no support for mmap, user-space interrupt management
+and DMA buffers. They may be added in later versions, if the need
+arises.
+
+The example below shows raw access to a SPEC card programmed with its
+golden FPGA file, that features an SDB structure at offset 256 - i.e.
+64 words.  The mezzanine's EEPROM in this case is not programmed, so the
+default name is fmc-<bus><devfn>, and there are two cards in the system:
+
+  spusa.root# insmod fmc-chardev.ko
+  [ 1073.339332] spec 0000:02:00.0: Driver has no ID: matches all
+  [ 1073.345051] spec 0000:02:00.0: Created misc device "fmc-0200"
+  [ 1073.350821] spec 0000:04:00.0: Driver has no ID: matches all
+  [ 1073.356525] spec 0000:04:00.0: Created misc device "fmc-0400"
+  spusa.root# ls -l /dev/fmc*
+  crw------- 1 root root 10, 58 Nov 20 19:23 /dev/fmc-0200
+  crw------- 1 root root 10, 57 Nov 20 19:23 /dev/fmc-0400
+  spusa.root# dd bs=4 skip=64 count=1 if=/dev/fmc-0200 2> /dev/null | od -t x1z
+  0000000 2d 42 44 53                                      >-BDS<
+  0000004
+
+The simple program tools/fmc-mem in this package can access an FMC char
+device and read or write a word or a whole area.  Actually, the program
+is not specific to FMC at all, it just uses lseek, read and write.
+
+Its first argument is the device name, the second the offset, the third
+(if any) the value to write and the optional last argument that must
+begin with "+" is the number of bytes to read or write.  In case of
+repeated reading data is written to stdout; repeated writes read from
+stdin and the value argument is ignored.
+
+The following examples show reading the SDB magic number and the first
+SDB record from a SPEC device programmed with its golden image:
+
+     spusa.root# ./fmc-mem /dev/fmc-0200 100
+     5344422d
+     spusa.root# ./fmc-mem /dev/fmc-0200 100 +40 | od -Ax -t x1z
+     000000 2d 42 44 53 00 01 02 00 00 00 00 00 00 00 00 00  >-BDS............<
+     000010 00 00 00 00 ff 01 00 00 00 00 00 00 51 06 00 00  >............Q...<
+     000020 c9 42 a5 e6 02 00 00 00 11 05 12 20 2d 34 42 57  >.B......... -4BW<
+     000030 73 6f 72 43 72 61 62 73 49 53 47 2d 00 20 20 20  >sorCrabsISG-.   <
+     000040

drivers/fmc/Kconfig

@@ -40,4 +40,12 @@ config FMC_WRITE_EEPROM
 	  its binary and the function carrier->reprogram to actually do it.
 	  It is useful when the mezzanines are produced.
 
+config FMC_CHARDEV
+	tristate "FMC mezzanine driver that registers a char device"
+	help
+	  This driver matches every mezzanine device and allows user
+	  space to read and write registers using a char device. It
+	  can be used to write user-space drivers, or just get
+	  aquainted with a mezzanine before writing its specific driver.
+
 endif # FMC

drivers/fmc/Makefile

@@ -10,3 +10,4 @@ fmc-y += fmc-dump.o
 obj-$(CONFIG_FMC_FAKEDEV) += fmc-fakedev.o
 obj-$(CONFIG_FMC_TRIVIAL) += fmc-trivial.o
 obj-$(CONFIG_FMC_WRITE_EEPROM) += fmc-write-eeprom.o
+obj-$(CONFIG_FMC_CHARDEV) += fmc-chardev.o

drivers/fmc/fmc-chardev.c

+/*
+ * Copyright (C) 2012 CERN (www.cern.ch)
+ * Author: Alessandro Rubini <rubini@gnudd.com>
+ *
+ * Released according to the GNU GPL, version 2 or any later version.
+ *
+ * This work is part of the White Rabbit project, a research effort led
+ * by CERN, the European Institute for Nuclear Research.
+ */
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/list.h>
+#include <linux/slab.h>
+#include <linux/fs.h>
+#include <linux/miscdevice.h>
+#include <linux/spinlock.h>
+#include <linux/fmc.h>
+#include <linux/uaccess.h>
+
+static LIST_HEAD(fc_devices);
+static DEFINE_SPINLOCK(fc_lock);
+
+struct fc_instance {
+	struct list_head list;
+	struct fmc_device *fmc;
+	struct miscdevice misc;
+};
+
+/* at open time, we must identify our device */
+static int fc_open(struct inode *ino, struct file *f)
+{
+	struct fmc_device *fmc;
+	struct fc_instance *fc;
+	int minor = iminor(ino);
+
+	list_for_each_entry(fc, &fc_devices, list)
+		if (fc->misc.minor == minor)
+			break;
+	if (fc->misc.minor != minor)
+		return -ENODEV;
+	fmc = fc->fmc;
+	if (try_module_get(fmc->owner) == 0)
+		return -ENODEV;
+
+	f->private_data = fmc;
+	return 0;
+}
+
+static int fc_release(struct inode *ino, struct file *f)
+{
+	struct fmc_device *fmc = f->private_data;
+	module_put(fmc->owner);
+	return 0;
+}
+
+/* read and write are simple after the default llseek has been used */
+static ssize_t fc_read(struct file *f, char __user *buf, size_t count,
+		       loff_t *offp)
+{
+	struct fmc_device *fmc = f->private_data;
+	unsigned long addr;
+	uint32_t val;
+
+	if (count < sizeof(val))
+		return -EINVAL;
+	count = sizeof(val);
+
+	addr = *offp;
+	if (addr > fmc->memlen)
+		return -ESPIPE; /* Illegal seek */
+	val = fmc_readl(fmc, addr);
+	if (copy_to_user(buf, &val, count))
+		return -EFAULT;
+	*offp += count;
+	return count;
+}
+
+static ssize_t fc_write(struct file *f, const char __user *buf, size_t count,
+			loff_t *offp)
+{
+	struct fmc_device *fmc = f->private_data;
+	unsigned long addr;
+	uint32_t val;
+
+	if (count < sizeof(val))
+		return -EINVAL;
+	count = sizeof(val);
+
+	addr = *offp;
+	if (addr > fmc->memlen)
+		return -ESPIPE; /* Illegal seek */
+	if (copy_from_user(&val, buf, count))
+		return -EFAULT;
+	fmc_writel(fmc, val, addr);
+	*offp += count;
+	return count;
+}
+
+static const struct file_operations fc_fops = {
+	.owner = THIS_MODULE,
+	.open = fc_open,
+	.release = fc_release,
+	.llseek = generic_file_llseek,
+	.read = fc_read,
+	.write = fc_write,
+};
+
+
+/* Device part .. */
+static int fc_probe(struct fmc_device *fmc);
+static int fc_remove(struct fmc_device *fmc);
+
+static struct fmc_driver fc_drv = {
+	.version = FMC_VERSION,
+	.driver.name = KBUILD_MODNAME,
+	.probe = fc_probe,
+	.remove = fc_remove,
+	/* no table: we want to match everything */
+};
+
+/* We accept the generic busid parameter */
+FMC_PARAM_BUSID(fc_drv);
+
+/* probe and remove must allocate and release a misc device */
+static int fc_probe(struct fmc_device *fmc)
+{
+	int ret;
+	int index = 0;
+
+	struct fc_instance *fc;
+
+	if (fmc->op->validate)
+		index = fmc->op->validate(fmc, &fc_drv);
+	if (index < 0)
+		return -EINVAL; /* not our device: invalid */
+
+	/* Create a char device: we want to create it anew */
+	fc = kzalloc(sizeof(*fc), GFP_KERNEL);
+	fc->fmc = fmc;
+	fc->misc.minor = MISC_DYNAMIC_MINOR;
+	fc->misc.fops = &fc_fops;
+	fc->misc.name = kstrdup(dev_name(&fmc->dev), GFP_KERNEL);
+
+	spin_lock(&fc_lock);
+	ret = misc_register(&fc->misc);
+	if (ret < 0) {
+		kfree(fc->misc.name);
+		kfree(fc);
+	} else {
+		list_add(&fc->list, &fc_devices);
+	}
+	spin_unlock(&fc_lock);
+	dev_info(&fc->fmc->dev, "Created misc device \"%s\"\n",
+		 fc->misc.name);
+	return ret;
+}
+
+static int fc_remove(struct fmc_device *fmc)
+{
+	struct fc_instance *fc;
+
+	list_for_each_entry(fc, &fc_devices, list)
+		if (fc->fmc == fmc)
+			break;
+	if (fc->fmc != fmc) {
+		dev_err(&fmc->dev, "remove called but not found\n");
+		return -ENODEV;
+	}
+
+	spin_lock(&fc_lock);
+	list_del(&fc->list);
+	misc_deregister(&fc->misc);
+	kfree(fc->misc.name);
+	kfree(fc);
+	spin_unlock(&fc_lock);
+
+	return 0;
+}
+
+
+static int fc_init(void)
+{
+	int ret;
+
+	ret = fmc_driver_register(&fc_drv);
+	return ret;
+}
+
+static void fc_exit(void)
+{
+	fmc_driver_unregister(&fc_drv);
+}
+
+module_init(fc_init);
+module_exit(fc_exit);
+
+MODULE_LICENSE("GPL");