Subject: ACPI: Avoid bogus EC timeout when EC is in Polling mode
>From : Zhao Yakui <yakui.zhao@xxxxxxxxx>
When EC is in Polling mode, OS will check the EC status continually by using
the following source code:
clear_bit(EC_FLAGS_WAIT_GPE, &ec->flags);
while (time_before(jiffies, delay)) {
if (acpi_ec_check_status(ec, event))
return 0;
msleep(1);
}
But msleep is realized by the function of schedule_timeout. At the same time
although one process is already waken up by some events, it won't be scheduled
immediately. So maybe there exists the following phenomena:
a. The current jiffies is already after the predefined jiffies.
But before timeout happens, OS has no chance to check the EC
status again.
b. If preemptible schedule is enabled, maybe preempt schedule will happen
before checking loop. When the process is resumed again, maybe
timeout already happens, which means that OS has no chance to check
the EC status.
In such case maybe EC status is already what OS expects when timeout happens.
But OS has no chance to check the EC status and regards it as AE_TIME.
So it will be more appropriate that OS will try to check the EC status again
when timeout happens. If the EC status is what we expect, it won't be regarded
as timeout. Only when the EC status is not what we expect, it will be regarded
as timeout, which means that EC controller can't give a response in time.
http://bugzilla.kernel.org/show_bug.cgi?id=9823
http://bugzilla.kernel.org/show_bug.cgi?id=11141
Signed-off-by: Zhao Yakui <yakui.zhao@xxxxxxxxx>
Signed-off-by: Zhang Rui <rui.zhang@xxxxxxxxx>
---
drivers/acpi/ec.c | 2 ++
1 file changed, 2 insertions(+)
Index: linux-2.6/drivers/acpi/ec.c
===================================================================
--- linux-2.6.orig/drivers/acpi/ec.c
+++ linux-2.6/drivers/acpi/ec.c
@@ -196,6 +196,8 @@ static int acpi_ec_wait(struct acpi_ec *
return 0;
msleep(1);
}
+ if (acpi_ec_check_status(ec,event))
+ return 0;
}
pr_err(PREFIX "acpi_ec_wait timeout, status = 0x%2.2x, event = %s\n",
acpi_ec_read_status(ec),
--
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