On Mon, 18 Jan 2016, Mark Rutland wrote:

On Fri, Jan 15, 2016 at 02:55:14PM +0800, Shannon Zhao wrote:

quoted

From: Shannon Zhao <redacted>

ACPI 6.0 introduces a new table STAO to list the devices which are used
by Xen and can't be used by Dom0. On Xen virtual platforms, the physical
UART is used by Xen. So here it hides UART from Dom0.

Signed-off-by: Shannon Zhao <redacted>
---
CC: "Rafael J. Wysocki" <redacted> (supporter:ACPI)
CC: Len Brown <redacted> (supporter:ACPI)
CC: linux-acpi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org (open list:ACPI)
---
 drivers/acpi/bus.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
index a212cef..d7a559f 100644
--- a/drivers/acpi/bus.c
+++ b/drivers/acpi/bus.c

@@ -46,6 +46,7 @@ ACPI_MODULE_NAME("bus");
 struct acpi_device *acpi_root;
 struct proc_dir_entry *acpi_root_dir;
 EXPORT_SYMBOL(acpi_root_dir);
+static u64 spcr_uart_addr;
 
 #ifdef CONFIG_X86
 #ifdef CONFIG_ACPI_CUSTOM_DSDT

@@ -93,6 +94,17 @@ acpi_status acpi_bus_get_status_handle(acpi_handle handle,
 {
 	acpi_status status;
 
+	if (spcr_uart_addr != 0xffffffffffffffff) {

The SPCR spec says that the Base Address fields being zero means that
console redirection is disabled (though I'm not clear on whether or not
that requires the whole acpi_generic_address to be zero).

Can we not use that here?

Shannon changed the code from 0 to 0xffffffffffffffff following my
suggestion to his previous series, but I didn't realize that the SPCR
spec says 0 means no console redirection. In that case using 0 is
better.