[RFC][PATCH] HPET: register additional counter-only char device

Dimitri Gorokhovik
2008-04-11T09:17:58Z

Hi,

I need to have many processes all reading from userspace the counter register
of the (same) HPET hardware. Just reading counter values, not handling timers,
enabling/disabling interrupts etc. `/dev/hpet' doesn't allow for this, as the
number of times it can be opened is limited by the number of timers available.

What would be the right way to implement such a support? For now, I simply
register a new misc device, '/dev/hpetctr', along with '/dev/hpet', for the same
ACPI device and on the same occasion.

Tested on 2.6.24-86_64-rt4 and on 2.6.25-rc8-git8.

---

Register a device `/dev/hpetctr' (10:229) giving access to the counter
of a HPET hw module. The available operations are: `open', `close' and
a read-only `mmap'. Contrary to `dev/hpet' it can be opened an unlimited
number of times. `read' not provided because of the cost of the system
call making the operation pointless.

Signed-off-by: Dimitri Gorokhovik <dimitri.gorokhovik@free.fr>
---
drivers/char/hpet.c | 71 +++++++++++++++++++++++++++++++++++++++++++++
include/linux/miscdevice.h | 1
2 files changed, 72 insertions(+)

diff --git a/drivers/char/hpet.c b/drivers/char/hpet.c
index 1399971..d94c3ce 100644
--- a/drivers/char/hpet.c
+++ b/drivers/char/hpet.c
@@ -218,6 +218,24 @@ static int hpet_open(struct inode *inode, struct file *file)
return 0;
}

+static int hpetctr_open(struct inode *inode, struct file *file)
+{
+ if (file->f_mode & FMODE_WRITE)
+ return -EINVAL;
+
+ spin_lock_irq(&hpet_lock);
+
+ if (hpets == NULL) {
+ spin_unlock_irq(&hpet_lock);
+ return -ENOSYS;
+ }
+
+ file->private_data = (void *)hpets->hp_hpet_phys;
+ spin_unlock_irq(&hpet_lock);
+
+ return 0;
+}
+
static ssize_t
hpet_read(struct file *file, char __user *buf, size_t count, loff_t * ppos)
{
@@ -318,6 +336,34 @@ static int hpet_mmap(struct file *file, struct vm_area_struct *vma)
#endif
}

+
+static int hpetctr_mmap(struct file *file, struct vm_area_struct *vma)
+{
+ unsigned long addr;
+
+ if (((vma->vm_end - vma->vm_start) != PAGE_SIZE) || vma->vm_pgoff)
+ return -EINVAL;
+
+ if (pgprot_val(vma->vm_page_prot) != pgprot_val(PAGE_READONLY))
+ return -EPERM;
+
+ addr = (unsigned long)file->private_data;
+ if (addr & (PAGE_SIZE - 1))
+ return -ENOSYS;
+
+ 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 "%s: io_remap_pfn_range failed\n",
+ __FUNCTION__);
+ return -EAGAIN;
+ }
+
+ return 0;
+}
+
static int hpet_fasync(int fd, struct file *file, int on)
{
struct hpet_dev *devp;
@@ -371,6 +417,13 @@ static int hpet_release(struct inode *inode, struct file *file)
return 0;
}

+static int hpetctr_release(struct inode *inode, struct file *file)
+{
+ file->private_data = NULL;
+ return 0;
+}
+
+
static int hpet_ioctl_common(struct hpet_dev *, int, unsigned long, int);

static int
@@ -589,6 +642,14 @@ static const struct file_operations hpet_fops = {
.mmap = hpet_mmap,
};

+static const struct file_operations hpetctr_fops = {
+ .owner = THIS_MODULE,
+ .llseek = no_llseek,
+ .open = hpetctr_open,
+ .release = hpetctr_release,
+ .mmap = hpetctr_mmap,
+};
+
static int hpet_is_known(struct hpet_data *hdp)
{
struct hpets *hpetp;
@@ -954,6 +1015,9 @@ static struct acpi_driver hpet_acpi_driver = {
};

static struct miscdevice hpet_misc = { HPET_MINOR, "hpet", &hpet_fops };
+static struct miscdevice hpetctr_misc = {
+ HPETCTR_MINOR, "hpetctr", &hpetctr_fops
+};

static int __init hpet_init(void)
{
@@ -973,11 +1037,18 @@ static int __init hpet_init(void)
return result;
}

+ result = misc_register(&hpetctr_misc);
+ if (result < 0)
+ printk(KERN_ERR "%s: failed to register '/dev/hpetctr'\n",
+ __FUNCTION__);
+
return 0;
}

static void __exit hpet_exit(void)
{
+ misc_deregister(&hpetctr_misc);
+
acpi_bus_unregister_driver(&hpet_acpi_driver);

if (sysctl_header)
diff --git a/include/linux/miscdevice.h b/include/linux/miscdevice.h
index 24b30b9..76c9b76 100644
--- a/include/linux/miscdevice.h
+++ b/include/linux/miscdevice.h
@@ -29,6 +29,7 @@

#define TUN_MINOR 200
#define HPET_MINOR 228
+#define HPETCTR_MINOR 229
#define KVM_MINOR 232

struct device;