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
Tested-by: Bob McElrath
---
drivers/hwmon/applesmc.c | 22 ++++++++++++----------
1 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/drivers/hwmon/applesmc.c b/drivers/hwmon/applesmc.c
index 321dc82..c6b9ecf 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 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));
--
1.5.6.3

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