diff mbox

[v4,01/17] Xen: ACPI: Hide UART used by Xen

Message ID 1454641552-12576-2-git-send-email-zhaoshenglong@huawei.com
State New, archived
Headers show

Commit Message

Shannon Zhao Feb. 5, 2016, 3:05 a.m. UTC
From: Shannon Zhao <shannon.zhao@linaro.org>

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 <shannon.zhao@linaro.org>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
---
CC: "Rafael J. Wysocki" <rjw@rjwysocki.net> (supporter:ACPI)
CC: Len Brown <lenb@kernel.org> (supporter:ACPI)
CC: linux-acpi@vger.kernel.org (open list:ACPI)
---
 drivers/acpi/bus.c | 38 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 37 insertions(+), 1 deletion(-)

Comments

Rafael J. Wysocki Feb. 6, 2016, 10:23 a.m. UTC | #1
On Fri, Feb 5, 2016 at 4:05 AM, Shannon Zhao <zhaoshenglong@huawei.com> wrote:
> From: Shannon Zhao <shannon.zhao@linaro.org>
>
> 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 <shannon.zhao@linaro.org>
> Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

Well, this doesn't look right to me.

We need to find a nicer way to achieve what you want.

Thanks,
Rafael
Stefano Stabellini Feb. 8, 2016, 10:57 a.m. UTC | #2
On Sat, 6 Feb 2016, Rafael J. Wysocki wrote:
> On Fri, Feb 5, 2016 at 4:05 AM, Shannon Zhao <zhaoshenglong@huawei.com> wrote:
> > From: Shannon Zhao <shannon.zhao@linaro.org>
> >
> > 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 <shannon.zhao@linaro.org>
> > Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> 
> Well, this doesn't look right to me.
> 
> We need to find a nicer way to achieve what you want.

I take that you are talking about how to honor the STAO table in Linux.
Do you have any concrete suggestions?
Rafael J. Wysocki Feb. 8, 2016, 10:25 p.m. UTC | #3
On Monday, February 08, 2016 10:57:01 AM Stefano Stabellini wrote:
> On Sat, 6 Feb 2016, Rafael J. Wysocki wrote:
> > On Fri, Feb 5, 2016 at 4:05 AM, Shannon Zhao <zhaoshenglong@huawei.com> wrote:
> > > From: Shannon Zhao <shannon.zhao@linaro.org>
> > >
> > > 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 <shannon.zhao@linaro.org>
> > > Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> > 
> > Well, this doesn't look right to me.
> > 
> > We need to find a nicer way to achieve what you want.
> 
> I take that you are talking about how to honor the STAO table in Linux.
> Do you have any concrete suggestions?

I do.

The last hunk of the patch is likely what it needs to be, although I'm
not sure if the place it is added to is the right one.  That's a minor thing,
though.

The other part is problematic.  Not that as it doesn't work, but because of
how it works.  With these changes the device will be visible to the OS (in
fact to user space even), but will never be "present".  I'm not sure if
that's what you want?

It might be better to add a check to acpi_bus_type_and_status() that will
evaluate the "should ignore?" thing and return -ENODEV if this is true.  This
way the device won't be visible at all.

Thanks,
Rafael
diff mbox

Patch

diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
index 891c42d..5b5433d 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
@@ -105,6 +106,22 @@  acpi_status acpi_bus_get_status_handle(acpi_handle handle,
 	return status;
 }
 
+static bool acpi_check_device_is_ignored(acpi_handle handle)
+{
+	acpi_status status;
+	u64 addr;
+
+	/* Check if it should ignore the UART device */
+	if (spcr_uart_addr != 0) {
+		status = acpi_evaluate_integer(handle, METHOD_NAME__ADR, NULL,
+					       &addr);
+		if (ACPI_SUCCESS(status) && addr == spcr_uart_addr)
+			return true;
+	}
+
+	return false;
+}
+
 int acpi_bus_get_status(struct acpi_device *device)
 {
 	acpi_status status;
@@ -114,7 +131,8 @@  int acpi_bus_get_status(struct acpi_device *device)
 	if (ACPI_FAILURE(status))
 		return -ENODEV;
 
-	acpi_set_device_status(device, sta);
+	if (!acpi_check_device_is_ignored(device->handle))
+		acpi_set_device_status(device, sta);
 
 	if (device->status.functional && !device->status.present) {
 		ACPI_DEBUG_PRINT((ACPI_DB_INFO, "Device [%s] status [%08x]: "
@@ -1070,6 +1088,8 @@  EXPORT_SYMBOL_GPL(acpi_kobj);
 static int __init acpi_init(void)
 {
 	int result;
+	acpi_status status;
+	struct acpi_table_stao *stao_ptr;
 
 	if (acpi_disabled) {
 		printk(KERN_INFO PREFIX "Interpreter disabled.\n");
@@ -1082,6 +1102,22 @@  static int __init acpi_init(void)
 		acpi_kobj = NULL;
 	}
 
+	/* If there is STAO table, check whether it needs to ignore the UART
+	 * device in SPCR table.
+	 */
+	status = acpi_get_table(ACPI_SIG_STAO, 0,
+				(struct acpi_table_header **)&stao_ptr);
+	if (ACPI_SUCCESS(status) && stao_ptr->ignore_uart) {
+		struct acpi_table_spcr *spcr_ptr;
+
+		status = acpi_get_table(ACPI_SIG_SPCR, 0,
+					(struct acpi_table_header **)&spcr_ptr);
+		if (ACPI_SUCCESS(status))
+			spcr_uart_addr = spcr_ptr->serial_port.address;
+		else
+			printk(KERN_WARNING "STAO table present, but SPCR is missing.\n");
+	}
+
 	init_acpi_device_notify();
 	result = acpi_bus_init();
 	if (result) {