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hwmon: applesmc: lighter wait mechanism, drastic improvement

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The read fail ratio is sensitive to the delay between the first byte
written and the first byte read; apparently the sensors cannot be rushed.
Increasing the minimum wait time, without changing the total wait time,
improves the fail ratio from a 8% chance that any of the sensors fails in
one read, down to 0.4%, on a Macbook Air.  On a Macbook Pro 3,1, the
effect is even more apparent.  By reducing the number of status polls, the
ratio is further improved to below 0.1%.  Finally, increasing the total
wait time brings the fail ratio down to virtually zero.

Signed-off-by: Henrik Rydberg <rydberg@euromail.se>
Tested-by: Bob McElrath <bob@mcelrath.org>
Cc: Nicolas Boichat <nicolas@boichat.ch>
Cc: "Mark M. Hoffman" <mhoffman@lightlink.com>
Cc: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Henrik Rydberg 2008-10-18 20:27:43 -07:00 committed by Linus Torvalds
parent 07e8dbd3eb
commit 8c9398d1e9
1 changed files with 12 additions and 10 deletions
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22
drivers/hwmon/applesmc.c
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@ -49,6 +49,9 @@
#define APPLESMC_MAX_DATA_LENGTH 32
#define APPLESMC_MIN_WAIT 0x0040
#define APPLESMC_MAX_WAIT 0x8000
#define APPLESMC_STATUS_MASK 0x0f
#define APPLESMC_READ_CMD 0x10
#define APPLESMC_WRITE_CMD 0x11
@ -172,25 +175,25 @@ static unsigned int key_at_index;
static struct workqueue_struct *applesmc_led_wq;
/*
* __wait_status - Wait up to 10ms for the status port to get a certain value
* __wait_status - Wait up to 32ms for the status port to get a certain value
* (masked with 0x0f), returning zero if the value is obtained. Callers must
* hold applesmc_lock.
*/
static int __wait_status(u8 val)
{
unsigned int i;
int us;
val = val & APPLESMC_STATUS_MASK;
for (i = 0; i < 1000; i++) {
for (us = APPLESMC_MIN_WAIT; us < APPLESMC_MAX_WAIT; us <<= 1) {
udelay(us);
if ((inb(APPLESMC_CMD_PORT) & APPLESMC_STATUS_MASK) == val) {
if (debug)
printk(KERN_DEBUG
"Waited %d us for status %x\n",
i*10, val);
"Waited %d us for status %x\n",
2 * us - APPLESMC_MIN_WAIT, val);
return 0;
}
udelay(10);
}
printk(KERN_WARNING "applesmc: wait status failed: %x != %x\n",
@ -206,13 +209,12 @@ static int __wait_status(u8 val)
*/
static int send_command(u8 cmd)
{
int i;
for (i = 0; i < 1000; i++) {
int us;
for (us = APPLESMC_MIN_WAIT; us < APPLESMC_MAX_WAIT; us <<= 1) {
outb(cmd, APPLESMC_CMD_PORT);
udelay(5);
udelay(us);
if ((inb(APPLESMC_CMD_PORT) & APPLESMC_STATUS_MASK) == 0x0c)
return 0;
udelay(5);
}
printk(KERN_WARNING "applesmc: command failed: %x -> %x\n",
cmd, inb(APPLESMC_CMD_PORT));