hwmon: applesmc: lighter wait mechanism, drastic improvement
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>
diff --git a/drivers/hwmon/applesmc.c b/drivers/hwmon/applesmc.c
index 59266ce..bc011da 100644
--- a/drivers/hwmon/applesmc.c
+++ b/drivers/hwmon/applesmc.c
@@ -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 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 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));