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Commit 8c9398d1 authored by Henrik Rydberg's avatar Henrik Rydberg Committed by Linus Torvalds
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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: default avatarHenrik Rydberg <rydberg@euromail.se>
Tested-by: default avatarBob 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 07e8dbd3

drivers/hwmon/applesmc.c

+12 −10
Original line number Diff line number Diff line
@@ -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);

					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));