Subject: ACPI: Add the 2us delay before starting check EC status while in polling mode
From: Zhao Yakui <yakui.zhao@xxxxxxxxx>
According to the ACPI spec when the host writes data to the command or data
register of the embedded controller, the input buffer flag (IBF) in the status
register is set within 1 microsecond. Maybe the incorrect status is returned by
EC if host checks the EC status immediately after the data is written to EC
I/O port.
On most laptosp it is unnecessary to add the delay as EC device is connected
with the slow peripherial bus. But it is safe to add the delay of 2 microseconds
before starting loop check the EC status while EC is in polling mode.
Signed-off-by: Zhao Yakui <yakui.zhao@xxxxxxxxx>
---
drivers/acpi/ec.c | 1 +
1 file changed, 1 insertion(+)
Index: linux-2.6/drivers/acpi/ec.c
===================================================================
--- linux-2.6.orig/drivers/acpi/ec.c
+++ linux-2.6/drivers/acpi/ec.c
@@ -260,6 +260,7 @@ static int acpi_ec_wait(struct acpi_ec *
} else {
unsigned long delay = jiffies + msecs_to_jiffies(ACPI_EC_DELAY);
clear_bit(EC_FLAGS_WAIT_GPE, &ec->flags);
+ udelay(2);
while (time_before(jiffies, delay)) {
if (acpi_ec_check_status(ec, event))
return 0;
--
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