ACPI / scan: Add acpi_device objects for all device nodes in the namespace

Modify the ACPI namespace scanning code to register a struct
acpi_device object for every namespace node representing a device,
processor and so on, even if the device represented by that namespace
node is reported to be not present and not functional by _STA.

There are multiple reasons to do that.  First of all, it avoids
quite a lot of overhead when struct acpi_device objects are
deleted every time acpi_bus_trim() is run and then added again
by a subsequent acpi_bus_scan() for the same scope, although the
namespace objects they correspond to stay in memory all the time
(which always is the case on a vast majority of systems).

Second, it will allow user space to see that there are namespace
nodes representing devices that are not present at the moment and may
be added to the system.  It will also allow user space to evaluate
_SUN for those nodes to check what physical slots the "missing"
devices may be put into and it will make sense to add a sysfs
attribute for _STA evaluation after this change (that will be
useful for thermal management on some systems).

Next, it will help to consolidate the ACPI hotplug handling among
subsystems by making it possible to store hotplug-related information
in struct acpi_device objects in a standard common way.

Finally, it will help to avoid a race condition related to the
deletion of ACPI namespace nodes.  Namely, namespace nodes may be
deleted as a result of a table unload triggered by _EJ0 or _DCK.
If a hotplug notification for one of those nodes is triggered
right before the deletion and it executes a hotplug callback
via acpi_hotplug_execute(), the ACPI handle passed to that
callback may be stale when the callback actually runs.  One way
to work around that is to always pass struct acpi_device pointers
to hotplug callbacks after doing a get_device() on the objects in
question which eliminates the use-after-free possibility (the ACPI
handles in those objects are invalidated by acpi_scan_drop_device(),
so they will trigger ACPICA errors on attempts to use them).

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Mika Westerberg <mika.westerberg@linux.intel.com>

1 files changed, 1 insertions, 8 deletions

diff --git a/Documentation/acpi/namespace.txt b/Documentation/acpi/namespace.txt
index 260f6a3661fa..1860cb3865c6 100644
--- a/Documentation/acpi/namespace.txt
+++ b/Documentation/acpi/namespace.txt
@@ -235,10 +235,6 @@ Wysocki <rafael.j.wysocki@intel.com>.
       named object's type in the second column).  In that case the object's
       directory in sysfs will contain the 'path' attribute whose value is
       the full path to the node from the namespace root.
-      struct acpi_device objects are created for the ACPI namespace nodes
-      whose _STA control methods return PRESENT or FUNCTIONING.  The power
-      resource nodes or nodes without _STA are assumed to be both PRESENT
-      and FUNCTIONING.
    F:
       The struct acpi_device object is created for a fixed hardware
       feature (as indicated by the fixed feature flag's name in the second
@@ -340,7 +336,7 @@ Wysocki <rafael.j.wysocki@intel.com>.
      | +-------------+-------+----------------+
      |   |
      |   | +- - - - - - - +- - - - - - +- - - - - - - -+
-     |   +-| * PNP0C0D:00 | \_SB_.LID0 | acpi:PNP0C0D: |
+     |   +-| PNP0C0D:00 | \_SB_.LID0 | acpi:PNP0C0D: |
      |   | +- - - - - - - +- - - - - - +- - - - - - - -+
      |   |
      |   | +------------+------------+-----------------------+
@@ -390,6 +386,3 @@ Wysocki <rafael.j.wysocki@intel.com>.
             attribute (as described earlier in this document).
    NOTE: N/A indicates the device object does not have the 'path' or the
          'modalias' attribute.
-   NOTE: The PNP0C0D device listed above is highlighted (marked by "*")
-         to indicate it will be created only when its _STA methods return
-         PRESENT or FUNCTIONING.