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authorZhao Yakui <yakui.zhao@intel.com>2008-09-23 13:38:13 +0800
committerGreg Kroah-Hartman <gregkh@suse.de>2008-10-08 19:44:41 -0700
commitdc317ed0f9cb83f616b95ae6abdba44832c60f39 (patch)
parent80ad012478ee989402ac014aab956e4534acd498 (diff)
ACPI: Avoid bogus EC timeout when EC is in Polling mode
commit 9d699ed92a459cb408e2577e8bbeabc8ec3989e1 upstream 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> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
1 files changed, 2 insertions, 0 deletions
diff --git a/drivers/acpi/ec.c b/drivers/acpi/ec.c
index 7222a18a0319..a9b8796ee628 100644
--- a/drivers/acpi/ec.c
+++ b/drivers/acpi/ec.c
@@ -228,6 +228,8 @@ static int acpi_ec_wait(struct acpi_ec *ec, enum ec_event event, int force_poll)
if (acpi_ec_check_status(ec, event))
goto end;
+ if (acpi_ec_check_status(ec,event))
+ return 0;
pr_err(PREFIX "acpi_ec_wait timeout,"
" status = %d, expect_event = %d\n",