ACPI: Avoid bogus EC timeout when EC is in Polling mode

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@intel.com>
Signed-off-by: Zhang Rui  <rui.zhang@intel.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

diff --git a/drivers/acpi/ec.c b/drivers/acpi/ec.c
index 76784ae..13593f9 100644 (file)
--- a/drivers/acpi/ec.c
+++ b/drivers/acpi/ec.c
@@ -221,6 +221,8 @@ static int acpi_ec_wait(struct acpi_ec *ec, enum ec_event event, int force_poll)
                                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),