watchdog: Add a simple mmap() stub for shwdt.

In some applications people have expressed a need for an mmap() method,
so we implement a simple stub for this that maps back a page with the
counter in it.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>

2 files changed, 59 insertions, 1 deletions

diff --git a/drivers/char/watchdog/Kconfig b/drivers/char/watchdog/Kconfig
index fff89c2d88fd..f114d7b5bb2a 100644
--- a/drivers/char/watchdog/Kconfig
+++ b/drivers/char/watchdog/Kconfig
@@ -510,6 +510,14 @@ config SH_WDT
           To compile this driver as a module, choose M here: the
           module will be called shwdt.
 
+config SH_WDT_MMAP
+        bool "Allow mmap of SH WDT"
+        default n
+        depends on SH_WDT
+        help
+          If you say Y here, user applications will be able to mmap the
+          WDT/CPG registers.
+#
 # SPARC64 Architecture
 
 config WATCHDOG_CP1XXX
diff --git a/drivers/char/watchdog/shwdt.c b/drivers/char/watchdog/shwdt.c
index 7c39f39effdf..e5b8c64f1d65 100644
--- a/drivers/char/watchdog/shwdt.c
+++ b/drivers/char/watchdog/shwdt.c
@@ -27,7 +27,7 @@
 #include <linux/notifier.h>
 #include <linux/ioport.h>
 #include <linux/fs.h>
-
+#include <linux/mm.h>
 #include <asm/io.h>
 #include <asm/uaccess.h>
 #include <asm/watchdog.h>
@@ -258,6 +258,55 @@ static ssize_t sh_wdt_write(struct file *file, const char *buf,
 }
 
 /**
+ *      sh_wdt_mmap - map WDT/CPG registers into userspace
+ *      @file: file structure for the device
+ *      @vma: VMA to map the registers into
+ *
+ *      A simple mmap() implementation for the corner cases where the counter
+ *      needs to be mapped in userspace directly. Due to the relatively small
+ *      size of the area, neighbouring registers not necessarily tied to the
+ *      CPG will also be accessible through the register page, so this remains
+ *      configurable for users that really know what they're doing.
+ *
+ *      Additionaly, the register page maps in the CPG register base relative
+ *      to the nearest page-aligned boundary, which requires that userspace do
+ *      the appropriate CPU subtype math for calculating the page offset for
+ *      the counter value.
+ */
+static int sh_wdt_mmap(struct file *file, struct vm_area_struct *vma)
+{
+        int ret = -ENOSYS;
+
+#ifdef CONFIG_SH_WDT_MMAP
+        unsigned long addr;
+
+        /* Only support the simple cases where we map in a register page. */
+        if (((vma->vm_end - vma->vm_start) != PAGE_SIZE) || vma->vm_pgoff)
+                return -EINVAL;
+
+        /*
+         * Pick WTCNT as the start, it's usually the first register after the
+         * FRQCR, and neither one are generally page-aligned out of the box.
+         */
+        addr = WTCNT & ~(PAGE_SIZE - 1);
+
+        vma->vm_flags |= VM_IO;
+        vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
+
+        if (io_remap_pfn_range(vma, vma->vm_start, addr >> PAGE_SHIFT,
+                               PAGE_SIZE, vma->vm_page_prot)) {
+                printk(KERN_ERR PFX "%s: io_remap_pfn_range failed\n",
+                       __FUNCTION__);
+                return -EAGAIN;
+        }
+
+        ret = 0;
+#endif
+
+        return ret;
+}
+
+/**
  *      sh_wdt_ioctl - Query Device
  *      @inode: inode of device
  *      @file: file handle of device
@@ -342,6 +391,7 @@ static const struct file_operations sh_wdt_fops = {
         .ioctl          = sh_wdt_ioctl,
         .open           = sh_wdt_open,
         .release        = sh_wdt_close,
+        .mmap           = sh_wdt_mmap,
 };
 
 static struct watchdog_info sh_wdt_info = {