From 4d6bdc58f9133b6970cc46ba7af9ae12927b38f3 Mon Sep 17 00:00:00 2001 From: Magnus Lynch Date: Thu, 25 Aug 2011 09:47:23 +1000 Subject: [PATCH] The current implementation of the /dev/hpet driver couples opening the device with allocating one of the (scarce) timers (aka comparators). This is a limitation in that the main counter may be valuable to applications seeking a high-resolution timer who have no use for the interrupt generating functionality of the comparators. This patch alters the open semantics so that when the device is opened, no timer is allocated. Operations that depend on a timer being in context implicitly attempt allocating a timer, to maintain backward compatibility. There is also an IOCTL (HPET_ALLOC_TIMER _IO) added so that the allocation may be done explicitly. (I prefer the explicit open then allocate pattern but don't know how practical it would be to require all existing code to be changed.) /dev/hpet is accessed via mmap(). This is the only interface of /dev/hpet that is actually used in practice. [akpm@linux-foundation.org: coding-style tweaks] [arnd@arndb.de: fix build] Signed-off-by: Magnus Lynch Cc: Thomas Gleixner Cc: john stultz Acked-by: Clemens Ladisch Signed-off-by: Arnd Bergmann Signed-off-by: Andrew Morton --- drivers/char/hpet.c | 56 ++++++++++++++++++++++++++++++++++++++------ include/linux/hpet.h | 1 + 2 files changed, 50 insertions(+), 7 deletions(-) diff --git a/drivers/char/hpet.c b/drivers/char/hpet.c index 0833896cf6f2..c9aeb7fce878 100644 --- a/drivers/char/hpet.c +++ b/drivers/char/hpet.c @@ -263,16 +263,40 @@ static void hpet_timer_set_irq(struct hpet_dev *devp) static int hpet_open(struct inode *inode, struct file *file) { - struct hpet_dev *devp; struct hpets *hpetp; - int i; if (file->f_mode & FMODE_WRITE) return -EINVAL; + hpetp = hpets; + /* starting with timer-neutral instance */ + file->private_data = &hpetp->hp_dev[hpetp->hp_ntimer]; + + return 0; +} + +static int hpet_alloc_timer(struct file *file) +{ + struct hpet_dev *devp; + struct hpets *hpetp; + int i; + + /* once acquired, will remain */ + devp = file->private_data; + if (devp->hd_timer) + return 0; + mutex_lock(&hpet_mutex); spin_lock_irq(&hpet_lock); + /* check for race acquiring */ + devp = file->private_data; + if (devp->hd_timer) { + spin_unlock_irq(&hpet_lock); + mutex_unlock(&hpet_mutex); + return 0; + } + for (devp = NULL, hpetp = hpets; hpetp && !devp; hpetp = hpetp->hp_next) for (i = 0; i < hpetp->hp_ntimer; i++) if (hpetp->hp_dev[i].hd_flags & HPET_OPEN) @@ -402,6 +426,11 @@ static int hpet_mmap(struct file *file, struct vm_area_struct *vma) static int hpet_fasync(int fd, struct file *file, int on) { struct hpet_dev *devp; + int r; + + r = hpet_alloc_timer(file); + if (r < 0) + return r; devp = file->private_data; @@ -420,6 +449,9 @@ static int hpet_release(struct inode *inode, struct file *file) devp = file->private_data; timer = devp->hd_timer; + if (!timer) + goto out; + spin_lock_irq(&hpet_lock); writeq((readq(&timer->hpet_config) & ~Tn_INT_ENB_CNF_MASK), @@ -444,7 +476,7 @@ static int hpet_release(struct inode *inode, struct file *file) if (irq) free_irq(irq, devp); - +out: file->private_data = NULL; return 0; } @@ -593,6 +625,9 @@ hpet_ioctl_common(struct hpet_dev *devp, int cmd, unsigned long arg, break; case HPET_IE_ON: return hpet_ioctl_ieon(devp); + case HPET_ALLOC_TIMER: + /* nothing to do */ + return 0; default: return -EINVAL; } @@ -859,7 +894,11 @@ int hpet_alloc(struct hpet_data *hdp) return 0; } - siz = sizeof(struct hpets) + ((hdp->hd_nirqs - 1) * + /* + * last hpet_dev will have null timer pointer, gives timer-neutral + * representation of block + */ + siz = sizeof(struct hpets) + ((hdp->hd_nirqs) * sizeof(struct hpet_dev)); hpetp = kzalloc(siz, GFP_KERNEL); @@ -925,13 +964,16 @@ int hpet_alloc(struct hpet_data *hdp) writeq(mcfg, &hpet->hpet_config); } - for (i = 0, devp = hpetp->hp_dev; i < hpetp->hp_ntimer; i++, devp++) { + for (i = 0, devp = hpetp->hp_dev; i < hpetp->hp_ntimer + 1; + i++, devp++) { struct hpet_timer __iomem *timer; - timer = &hpet->hpet_timers[devp - hpetp->hp_dev]; - devp->hd_hpets = hpetp; devp->hd_hpet = hpet; + if (i == hpetp->hp_ntimer) + continue; + + timer = &hpet->hpet_timers[devp - hpetp->hp_dev]; devp->hd_timer = timer; /* diff --git a/include/linux/hpet.h b/include/linux/hpet.h index 219ca4f6bea6..d690c0fe4b8b 100644 --- a/include/linux/hpet.h +++ b/include/linux/hpet.h @@ -125,6 +125,7 @@ struct hpet_info { #define HPET_EPI _IO('h', 0x04) /* enable periodic */ #define HPET_DPI _IO('h', 0x05) /* disable periodic */ #define HPET_IRQFREQ _IOW('h', 0x6, unsigned long) /* IRQFREQ usec */ +#define HPET_ALLOC_TIMER _IO('h', 0x7) #define MAX_HPET_TBS 8 /* maximum hpet timer blocks */ -- 2.39.5