acpi_os_stall
acpi_os_stall(100); /* 100 usec */
acpi_os_stall(how_long_us);
acpi_os_stall(10 * ACPI_USEC_PER_SEC);
acpi_os_stall(ACPI_USEC_PER_MSEC);
void acpi_os_stall(u32 microseconds);