[patch 2.6.26] /dev/hpet - fixes and cleanup

From: David Brownell
Date: Tue Jul 22 2008 - 18:09:18 EST

From: David Brownell <dbrownell@xxxxxxxxxxxxxxxxxxxxx>

Minor /dev/hpet updates and bugfixes:

* Remove dead code, mostly remnants of an incomplete/unusable
kernel interface ... noted when addressing "sparse" warnings:
+ hpet_unregister() and a routine it calls
+ hpet_task and all references, including hpet_task_lock
+ hpet_data.hd_flags (and HPET_DATA_PLATFORM)

* Correct and improve boot message:
+ displays *counter* (shared between comparators) bitwidth,
not *timer* bitwidths (which are often mixed)
+ relabel "timers" as "comparators"; this is less confusing,
they are not independent like normal timers are (sigh)
+ display MHz not Hz; it's never less than 10 MHz.

* Tighten and correct the userspace interface code
+ don't accidentally program comparators in 64-bit mode using
32-bit values ... always force comparators into 32-bit mode
+ only open comparators that have an interrupt, and can thus
perform "real work"
+ provide the correct bit definition flagging comparators with
periodic capability ... the ABI is unchanged

* Update Documentation/hpet.txt
+ be more correct and current
+ expand description a bit
+ don't mention that now-gone kernel interface

Plus, add a FIXME comment for something that could cause big trouble
on systems with more capable HPETs than at least Intel seems to ship.

I get the feeling few folk use this userspace interface, else those
nonfunctional IRQs would be causing more trouble.

Signed-off-by: David Brownell <dbrownell@xxxxxxxxxxxxxxxxxxxxx>
---
I CC'd everyone who MAINTAINERS says maintains HPET. Odd to have
four entries!!

And re that kernel interface: IMO, worth having a relatively
generic interface for hardware timers instead of inventing a new
interface for each new bit of hardware. Embedded systems tend to
have at least half a dozen SOC timers available...

Documentation/hpet.txt | 43 ++++++++++++-------------
arch/x86/kernel/hpet.c | 6 ++-
drivers/char/hpet.c | 82 +++++++++++--------------------------------------
include/linux/hpet.h | 16 ++-------
4 files changed, 50 insertions(+), 97 deletions(-)

--- a/Documentation/hpet.txt 2008-07-21 15:38:28.000000000 -0700
+++ b/Documentation/hpet.txt 2008-07-21 21:40:58.000000000 -0700
@@ -1,21 +1,32 @@
High Precision Event Timer Driver for Linux

-The High Precision Event Timer (HPET) hardware is the future replacement
-for the 8254 and Real Time Clock (RTC) periodic timer functionality.
-Each HPET can have up to 32 timers. It is possible to configure the
-first two timers as legacy replacements for 8254 and RTC periodic timers.
-A specification done by Intel and Microsoft can be found at
-<http://www.intel.com/technology/architecture/hpetspec.htm>.
+The High Precision Event Timer (HPET) hardware follows a specification
+by Intel and Microsoft which can be found at
+
+ http://www.intel.com/technology/architecture/hpetspec.htm
+
+Each HPET has one fixed-rate counter (at 10+ MHz, hence "High Precision")
+and up to 32 comparators. Normally three or more comparators are provided,
+each of which can generate oneshot interupts and at least one of which has
+additional hardware to support periodic interrupts. The comparators are
+also called "timers", which can be misleading since usually timers are
+independent of each other ... these share a counter, complicating resets.
+
+HPET devices can support two interrupt routing modes. In one mode, the
+comparators are additional interrupt sources with no particular system
+role. Many x86 BIOS writers don't route HPET interrupts at all, which
+prevents use of that mode. They support the other "legacy replacement"
+mode where the first two comparators block interrupts from 8254 timers
+and from the RTC.

The driver supports detection of HPET driver allocation and initialization
of the HPET before the driver module_init routine is called. This enables
platform code which uses timer 0 or 1 as the main timer to intercept HPET
initialization. An example of this initialization can be found in
-arch/i386/kernel/time_hpet.c.
+arch/x86/kernel/hpet.c.

-The driver provides two APIs which are very similar to the API found in
-the rtc.c driver. There is a user space API and a kernel space API.
-An example user space program is provided below.
+The driver provides a userspace API which resembles the API found in the
+RTC driver framework. An example user space program is provided below.

#include <stdio.h>
#include <stdlib.h>
@@ -286,15 +297,3 @@ out:

return;
}
-
-The kernel API has three interfaces exported from the driver:
-
- hpet_register(struct hpet_task *tp, int periodic)
- hpet_unregister(struct hpet_task *tp)
- hpet_control(struct hpet_task *tp, unsigned int cmd, unsigned long arg)
-
-The kernel module using this interface fills in the ht_func and ht_data
-members of the hpet_task structure before calling hpet_register.
-hpet_control simply vectors to the hpet_ioctl routine and has the same
-commands and respective arguments as the user API. hpet_unregister
-is used to terminate usage of the HPET timer reserved by hpet_register.
--- a/arch/x86/kernel/hpet.c 2008-07-21 18:59:49.000000000 -0700
+++ b/arch/x86/kernel/hpet.c 2008-07-21 19:43:04.000000000 -0700
@@ -127,13 +127,17 @@ static void hpet_reserve_platform_timers
hd.hd_phys_address = hpet_address;
hd.hd_address = hpet;
hd.hd_nirqs = nrtimers;
- hd.hd_flags = HPET_DATA_PLATFORM;
hpet_reserve_timer(&hd, 0);

#ifdef CONFIG_HPET_EMULATE_RTC
hpet_reserve_timer(&hd, 1);
#endif

+ /*
+ * NOTE that hd_irq[] reflects IOAPIC input pins (LEGACY_8254
+ * is wrong for i8259!) not the output IRQ. Many BIOS writers
+ * don't bother configuring *any* comparator interrupts.
+ */
hd.hd_irq[0] = HPET_LEGACY_8254;
hd.hd_irq[1] = HPET_LEGACY_RTC;

--- a/drivers/char/hpet.c 2008-07-21 15:38:28.000000000 -0700
+++ b/drivers/char/hpet.c 2008-07-21 21:41:16.000000000 -0700
@@ -76,7 +76,7 @@ static struct clocksource clocksource_hp
.rating = 250,
.read = read_hpet,
.mask = CLOCKSOURCE_MASK(64),
- .mult = 0, /*to be caluclated*/
+ .mult = 0, /*to be calculated*/
.shift = 10,
.flags = CLOCK_SOURCE_IS_CONTINUOUS,
};
@@ -85,8 +85,6 @@ static struct clocksource *hpet_clocksou

/* A lock for concurrent access by app and isr hpet activity. */
static DEFINE_SPINLOCK(hpet_lock);
-/* A lock for concurrent intermodule access to hpet and isr hpet activity. */
-static DEFINE_SPINLOCK(hpet_task_lock);

#define HPET_DEV_NAME (7)

@@ -98,7 +96,6 @@ struct hpet_dev {
unsigned long hd_irqdata;
wait_queue_head_t hd_waitqueue;
struct fasync_struct *hd_async_queue;
- struct hpet_task *hd_task;
unsigned int hd_flags;
unsigned int hd_irq;
unsigned int hd_hdwirq;
@@ -172,11 +169,6 @@ static irqreturn_t hpet_interrupt(int ir
writel(isr, &devp->hd_hpet->hpet_isr);
spin_unlock(&hpet_lock);

- spin_lock(&hpet_task_lock);
- if (devp->hd_task)
- devp->hd_task->ht_func(devp->hd_task->ht_data);
- spin_unlock(&hpet_task_lock);
-
wake_up_interruptible(&devp->hd_waitqueue);

kill_fasync(&devp->hd_async_queue, SIGIO, POLL_IN);
@@ -198,7 +190,7 @@ static int hpet_open(struct inode *inode
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
- || hpetp->hp_dev[i].hd_task)
+ || !hpetp->hp_dev[i].hd_hdwirq)
continue;
else {
devp = &hpetp->hp_dev[i];
@@ -437,7 +429,11 @@ static int hpet_ioctl_ieon(struct hpet_d
devp->hd_irq = irq;
t = devp->hd_ireqfreq;
v = readq(&timer->hpet_config);
- g = v | Tn_INT_ENB_CNF_MASK;
+
+ /* 64-bit comparators are not yet supported through the ioctls,
+ * so force this into 32-bit mode if it supports both modes
+ */
+ g = v | Tn_32MODE_CNF_MASK | Tn_INT_ENB_CNF_MASK;

if (devp->hd_flags & HPET_PERIODIC) {
write_counter(t, &timer->hpet_compare);
@@ -447,6 +443,12 @@ static int hpet_ioctl_ieon(struct hpet_d
v |= Tn_VAL_SET_CNF_MASK;
writeq(v, &timer->hpet_config);
local_irq_save(flags);
+
+ /* FIXME this may trash both the system clocksource and
+ * the current clock event device! Use HPET_TN_SETVAL
+ * instead, like arch/x86/kernel/hpet.c does ... never
+ * modify the counter, ever.
+ */
m = read_counter(&hpet->hpet_mc);
write_counter(t + m + hpetp->hp_delta, &timer->hpet_compare);
} else {
@@ -600,55 +602,6 @@ static int hpet_is_known(struct hpet_dat
return 0;
}

-static inline int hpet_tpcheck(struct hpet_task *tp)
-{
- struct hpet_dev *devp;
- struct hpets *hpetp;
-
- devp = tp->ht_opaque;
-
- if (!devp)
- return -ENXIO;
-
- for (hpetp = hpets; hpetp; hpetp = hpetp->hp_next)
- if (devp >= hpetp->hp_dev
- && devp < (hpetp->hp_dev + hpetp->hp_ntimer)
- && devp->hd_hpet == hpetp->hp_hpet)
- return 0;
-
- return -ENXIO;
-}
-
-int hpet_unregister(struct hpet_task *tp)
-{
- struct hpet_dev *devp;
- struct hpet_timer __iomem *timer;
- int err;
-
- if ((err = hpet_tpcheck(tp)))
- return err;
-
- spin_lock_irq(&hpet_task_lock);
- spin_lock(&hpet_lock);
-
- devp = tp->ht_opaque;
- if (devp->hd_task != tp) {
- spin_unlock(&hpet_lock);
- spin_unlock_irq(&hpet_task_lock);
- return -ENXIO;
- }
-
- timer = devp->hd_timer;
- writeq((readq(&timer->hpet_config) & ~Tn_INT_ENB_CNF_MASK),
- &timer->hpet_config);
- devp->hd_flags &= ~(HPET_IE | HPET_PERIODIC);
- devp->hd_task = NULL;
- spin_unlock(&hpet_lock);
- spin_unlock_irq(&hpet_task_lock);
-
- return 0;
-}
-
static ctl_table hpet_table[] = {
{
.ctl_name = CTL_UNNUMBERED,
@@ -803,9 +756,12 @@ int hpet_alloc(struct hpet_data *hdp)
printk("%s %d", i > 0 ? "," : "", hdp->hd_irq[i]);
printk("\n");

- printk(KERN_INFO "hpet%u: %u %d-bit timers, %Lu Hz\n",
- hpetp->hp_which, hpetp->hp_ntimer,
- cap & HPET_COUNTER_SIZE_MASK ? 64 : 32, hpetp->hp_tick_freq);
+ printk(KERN_INFO
+ "hpet%u: %u comparators, %d-bit %u.%06u MHz counter\n",
+ hpetp->hp_which, hpetp->hp_ntimer,
+ cap & HPET_COUNTER_SIZE_MASK ? 64 : 32,
+ (unsigned) (hpetp->hp_tick_freq / 1000000),
+ (unsigned) (hpetp->hp_tick_freq % 1000000));

mcfg = readq(&hpet->hpet_config);
if ((mcfg & HPET_ENABLE_CNF_MASK) == 0) {
--- a/include/linux/hpet.h 2008-07-21 15:38:28.000000000 -0700
+++ b/include/linux/hpet.h 2008-07-21 19:00:06.000000000 -0700
@@ -91,23 +91,14 @@ struct hpet {
* exported interfaces
*/

-struct hpet_task {
- void (*ht_func) (void *);
- void *ht_data;
- void *ht_opaque;
-};
-
struct hpet_data {
unsigned long hd_phys_address;
void __iomem *hd_address;
unsigned short hd_nirqs;
- unsigned short hd_flags;
unsigned int hd_state; /* timer allocated */
unsigned int hd_irq[HPET_MAX_TIMERS];
};

-#define HPET_DATA_PLATFORM 0x0001 /* platform call to hpet_alloc */
-
static inline void hpet_reserve_timer(struct hpet_data *hd, int timer)
{
hd->hd_state |= (1 << timer);
@@ -125,7 +119,7 @@ struct hpet_info {
unsigned short hi_timer;
};

-#define HPET_INFO_PERIODIC 0x0001 /* timer is periodic */
+#define HPET_INFO_PERIODIC 0x0010 /* periodic-capable comparator */

#define HPET_IE_ON _IO('h', 0x01) /* interrupt on */
#define HPET_IE_OFF _IO('h', 0x02) /* interrupt off */
--
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