[RFC PATCH v4] acpi: indicate to platform when hot remove returns busy

["Lee, Chun-Yi" <joeyli.kernel@gmail.com>]

In hotplug logic, it always indicates non-specific failure to
platform through _OST when handing acpi hot-remove event failed. Then
platform terminates the hot-remove process but it can not identify
the reason.

Base on current hot-remove code, there have two situations that it
returns busy:
 - OSPM try to offline an individual device, but the device offline
   function returns busy.
 - When the ejection event is applied to an "not offlined yet" container.
   OSPM send kobject change event to userspace and returns busy.

Both of them will returns -EBUSY to acpi device hotplug function then
hotplug function indicates non-specific failure to platform just like
any other error, e.g. -ENODEV or -EIO.

The benefit to platform for identifying the OS busy state is that
platform can be applied different approach to handle the busy but
not just terminate the hot-remove process by unknown reason. For
example, platform can wait for a while then triggers hot-remove
again.

This RFC patch adds one more parameter to the handler function of
acpi generic hotplug event to give the function a chance to propose
the return code of _OST. In this case, it sets ost return code to
ACPI_OST_SC_DEVICE_BUSY when the acpi hot remove function returns
-EBUSY.

v4:
Use switch-case statements to simplify code. (Andy Shevchenko, Rafael J. Wysocki)

v3:
Removed redundant 'else' in acpi_ost_status_code(). (Andy Shevchenko)

v2:
Do not overwrite ost code in acpi_generic_hotplug_event(). Move
the "error code to ost code" logic to a help function. (Andy Shevchenko)

Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Len Brown <lenb@kernel.org>
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Michal Hocko <mhocko@suse.cz>
Signed-off-by: "Lee, Chun-Yi" <jlee@suse.com>
---
 drivers/acpi/scan.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
index d531629..ce88175 100644
--- a/drivers/acpi/scan.c
+++ b/drivers/acpi/scan.c
@@ -404,10 +404,6 @@ void acpi_device_hotplug(struct acpi_device *adev, u32 src)
 		error = dock_notify(adev, src);
 	} else if (adev->flags.hotplug_notify) {
 		error = acpi_generic_hotplug_event(adev, src);
-		if (error == -EPERM) {
-			ost_code = ACPI_OST_SC_EJECT_NOT_SUPPORTED;
-			goto err_out;
-		}
 	} else {
 		int (*notify)(struct acpi_device *, u32);
 
@@ -423,8 +419,20 @@ void acpi_device_hotplug(struct acpi_device *adev, u32 src)
 		else
 			goto out;
 	}
-	if (!error)
+	switch (error) {
+	case 0:
 		ost_code = ACPI_OST_SC_SUCCESS;
+		break;
+	case -EPERM:
+		ost_code = ACPI_OST_SC_EJECT_NOT_SUPPORTED;
+		break;
+	case -EBUSY:
+		ost_code = ACPI_OST_SC_DEVICE_BUSY;
+		break;
+	default:
+		ost_code = ACPI_OST_SC_NON_SPECIFIC_FAILURE;
+		break;
+	}
 
  err_out:
 	acpi_evaluate_ost(adev->handle, src, ost_code, NULL);
-- 
2.10.2