Add the 2us delay before loop check EC status while in polling mode
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
@@ -259,6 +259,7 @@ 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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