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>
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@ -49,6 +49,9 @@
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#define APPLESMC_MAX_DATA_LENGTH 32
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#define APPLESMC_MIN_WAIT 0x0040
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#define APPLESMC_MAX_WAIT 0x8000
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#define APPLESMC_STATUS_MASK 0x0f
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#define APPLESMC_READ_CMD 0x10
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#define APPLESMC_WRITE_CMD 0x11
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@ -172,25 +175,25 @@ static unsigned int key_at_index;
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static struct workqueue_struct *applesmc_led_wq;
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/*
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* __wait_status - Wait up to 10ms for the status port to get a certain value
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* __wait_status - Wait up to 32ms for the status port to get a certain value
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* (masked with 0x0f), returning zero if the value is obtained. Callers must
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* hold applesmc_lock.
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*/
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static int __wait_status(u8 val)
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{
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unsigned int i;
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int us;
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val = val & APPLESMC_STATUS_MASK;
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for (i = 0; i < 1000; i++) {
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for (us = APPLESMC_MIN_WAIT; us < APPLESMC_MAX_WAIT; us <<= 1) {
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udelay(us);
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if ((inb(APPLESMC_CMD_PORT) & APPLESMC_STATUS_MASK) == val) {
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if (debug)
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printk(KERN_DEBUG
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"Waited %d us for status %x\n",
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i*10, val);
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"Waited %d us for status %x\n",
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2 * us - APPLESMC_MIN_WAIT, val);
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return 0;
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}
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udelay(10);
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}
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printk(KERN_WARNING "applesmc: wait status failed: %x != %x\n",
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@ -206,13 +209,12 @@ static int __wait_status(u8 val)
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*/
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static int send_command(u8 cmd)
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{
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int i;
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for (i = 0; i < 1000; i++) {
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int us;
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for (us = APPLESMC_MIN_WAIT; us < APPLESMC_MAX_WAIT; us <<= 1) {
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outb(cmd, APPLESMC_CMD_PORT);
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udelay(5);
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udelay(us);
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if ((inb(APPLESMC_CMD_PORT) & APPLESMC_STATUS_MASK) == 0x0c)
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return 0;
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udelay(5);
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}
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printk(KERN_WARNING "applesmc: command failed: %x -> %x\n",
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cmd, inb(APPLESMC_CMD_PORT));
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