On 2016/3/26 1:15, Bjorn Helgaas wrote:

On Fri, Mar 25, 2016 at 04:05:49PM +0800, Shannon Zhao wrote:

quoted

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.

CC: "Rafael J. Wysocki" <redacted> (supporter:ACPI)
CC: Len Brown <lenb@kernel.org> (supporter:ACPI)
CC: linux-acpi at vger.kernel.org (open list:ACPI)
Signed-off-by: Shannon Zhao <redacted>
---
 drivers/acpi/scan.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 68 insertions(+)

diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
index 5f28cf7..5420cc5 100644
--- a/drivers/acpi/scan.c
+++ b/drivers/acpi/scan.c

@@ -45,6 +45,7 @@ static LIST_HEAD(acpi_scan_handlers_list);
 DEFINE_MUTEX(acpi_device_lock);
 LIST_HEAD(acpi_wakeup_device_list);
 static DEFINE_MUTEX(acpi_hp_context_lock);
+static u64 spcr_uart_addr;
 
 struct acpi_dep_data {
 	struct list_head node;

@@ -1453,6 +1454,41 @@ static int acpi_add_single_object(struct acpi_device **child,
 	return 0;
 }
 
+static acpi_status acpi_get_resource_memory(struct acpi_resource *ares,
+					    void *context)
+{
+	struct resource *res = context;
+
+	if (acpi_dev_resource_memory(ares, res))
+		return AE_CTRL_TERMINATE;
+
+	return AE_OK;
+}
+
+static bool acpi_device_should_be_hidden(acpi_handle handle)
+{
+	acpi_status status;
+	struct resource res;
+
+	/* Check if it should ignore the UART device */
+	if (spcr_uart_addr != 0) {
+		if (!acpi_has_method(handle, METHOD_NAME__CRS))
+			return false;
+
+		status = acpi_walk_resources(handle, METHOD_NAME__CRS,
+					     acpi_get_resource_memory, &res);
+		if (ACPI_FAILURE(status))
+			return false;
+
+		if (res.start == spcr_uart_addr) {
+			printk(KERN_INFO PREFIX "The UART device in SPCR table will be hidden\n");

Can we at least print out the ACPI device path and address here for
debugging purposes?  IMHO, kernel messages that contain only static
text are always dubious.  There's almost always a useful address, IRQ,
return value, etc., that could be included.

Ok, I'll add the device address in the message and update this patch.

Thanks,
-- 
Shannon