ACPI / scan: Fix regression related to X-Gene UARTs

Message ID 20180420032947.23023-1-msalter@redhat.com
State New
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Series
  • ACPI / scan: Fix regression related to X-Gene UARTs
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Commit Message

Mark Salter April 20, 2018, 3:29 a.m.
Commit e361d1f85855 ("ACPI / scan: Fix enumeration for special UART
devices") caused a regression with some X-Gene based platforms (Mustang
and M400) with invalid DSDT. The DSDT makes it appear that the UART
device is also a slave device attached to itself. With the above commit
the UART won't be enumerated by ACPI scan (slave serial devices shouldn't
be). So check for X-Gene UART device and skip slace device check on it.

Signed-off-by: Mark Salter <msalter@redhat.com>

---
 drivers/acpi/scan.c | 8 ++++++++
 1 file changed, 8 insertions(+)

-- 
2.14.3

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Comments

Rafael J. Wysocki April 22, 2018, 9:34 a.m. | #1
On Fri, Apr 20, 2018 at 5:29 AM, Mark Salter <msalter@redhat.com> wrote:
> Commit e361d1f85855 ("ACPI / scan: Fix enumeration for special UART

> devices") caused a regression with some X-Gene based platforms (Mustang

> and M400) with invalid DSDT.


I'm not convinced that making changes to the core ACPI device
enumeration code in order to cover up for firmware bugs is the right
approach.

> The DSDT makes it appear that the UART

> device is also a slave device attached to itself. With the above commit

> the UART won't be enumerated by ACPI scan (slave serial devices shouldn't

> be). So check for X-Gene UART device and skip slace device check on it.

>

> Signed-off-by: Mark Salter <msalter@redhat.com>

> ---

>  drivers/acpi/scan.c | 8 ++++++++

>  1 file changed, 8 insertions(+)

>

> diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c

> index cc234e6a6297..1dcdd0122862 100644

> --- a/drivers/acpi/scan.c

> +++ b/drivers/acpi/scan.c

> @@ -1551,6 +1551,14 @@ static bool acpi_device_enumeration_by_parent(struct acpi_device *device)

>              fwnode_property_present(&device->fwnode, "baud")))

>                 return true;

>

> +       /*

> +        * Firmware on some arm64 X-Gene platforms will make the UART

> +        * device appear as both a UART and a slave of that UART. Just

> +        * bail out here for X-Gene UARTs.

> +        */

> +       if (!strcmp(acpi_device_hid(device), "APMC0D08"))

> +               return false;


Is the device ID never to be used outside of the broken configurations?

Even if that's the plan, how are you going to guarantee that anyway?

> +

>         INIT_LIST_HEAD(&resource_list);

>         acpi_dev_get_resources(device, &resource_list,

>                                acpi_check_serial_bus_slave,

> --

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Patch

diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
index cc234e6a6297..1dcdd0122862 100644
--- a/drivers/acpi/scan.c
+++ b/drivers/acpi/scan.c
@@ -1551,6 +1551,14 @@  static bool acpi_device_enumeration_by_parent(struct acpi_device *device)
 	     fwnode_property_present(&device->fwnode, "baud")))
 		return true;
 
+	/*
+	 * Firmware on some arm64 X-Gene platforms will make the UART
+	 * device appear as both a UART and a slave of that UART. Just
+	 * bail out here for X-Gene UARTs.
+	 */
+	if (!strcmp(acpi_device_hid(device), "APMC0D08"))
+		return false;
+
 	INIT_LIST_HEAD(&resource_list);
 	acpi_dev_get_resources(device, &resource_list,
 			       acpi_check_serial_bus_slave,