Re: [PATCH v3 13/17] ACPI: identify device tree root by null parent pointer, not ACPI_BUS_TYPE

ykzhao
2009-09-24T02:10:29Z

On Thu, 2009-09-24 at 00:14 +0800, Bjorn Helgaas wrote:
> On Tuesday 22 September 2009 09:09:44 pm ykzhao wrote:
> > On Tue, 2009-09-22 at 03:29 +0800, Bjorn Helgaas wrote:
> > > We can identify the root of the ACPI device tree by the fact that it
> > > has no parent. This is simpler than passing around ACPI_BUS_TYPE_SYSTEM
> > > and will help remove special treatment of the device tree root.
> > >
> > > Currently, we add the root by hand with ACPI_BUS_TYPE_SYSTEM. If we
> > > traverse the tree treating the root as just another device and use
> > > acpi_get_type(), the root shows up as ACPI_TYPE_DEVICE.
> > >
> > > Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
> > > ---
> > > drivers/acpi/scan.c | 20 +++++++++++++-------
> > > include/acpi/acpi_bus.h | 1 -
> > > 2 files changed, 13 insertions(+), 8 deletions(-)
> > >
> > > diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> > > index 27d2dec..0b5aaf0 100644
> > > --- a/drivers/acpi/scan.c
> > > +++ b/drivers/acpi/scan.c
> > > @@ -22,6 +22,8 @@ extern struct acpi_device *acpi_root;
> > > #define ACPI_BUS_HID "LNXSYBUS"
> > > #define ACPI_BUS_DEVICE_NAME "System Bus"
> > >
> > > +#define ACPI_IS_ROOT_DEVICE(device) (!(device)->parent)
>
> > the following definition will be better
> > #define ACPI_IS_ROOT_DEVICE(device) \
> > (device->handle == ACPI_ROOT_OBJECT)
>
> I wish you'd given me a clue about *why* you think it's better to
> check the handle.
Every acpi device has its corresponding acpi_handle. We can use this
info to check whether the device is the root device.

Of course it is also ok to check whether the device is the root device
by using device->parent.
>
> I considered checking the handle, but I used the parent pointer
> because:
>
> 1) There are synonyms for the root handle: ACPI_ROOT_OBJECT is the
> special-case #define to allow ACPICA users to start traversing
> the namespace before they know any handles, but acpi_gbl_root_node
> is the real root handle. In fact, if you call acpi_get_parent()
> on a child of the root, it returns acpi_gbl_root_node, not
> ACPI_ROOT_OBJECT. This is a bit messy, and it seems safest to
> me to just avoid testing against ACPI_ROOT_OBJECT at all.
>
> 2) It's a reminder that the acpi_device tree data structure should
> be a proper fully-connected tree with exactly one root. If we
> assume a valid tree, there's exactly one node with no parent.
> That's more fundamental than the handle, where you have to
> analyze more code to make sure we don't assign ACPI_ROOT_OBJECT
> to several nodes.
>
> (There is existing code that allows disconnected trees to be built.
> For example, dock_create_acpi_device() can call acpi_bus_add()
> with a NULL parent pointer. This "shouldn't happen," but I
> consider the fact that the interface allows this to be a bug.
> That's one reason I'm removing the "parent" argument from
> acpi_add_single_object() and related interfaces.)
>
> 3) We build acpi_devices for things with no handle, e.g., functional
> fixed hardware. Their handles happen to be NULL but I prefer to
> think of them as undefined and not rely on them at all.
Is it possible to build the acpi_device without acpi handle? It
seems that now we won't create a new acpi device for the functional
fixed hardware.For example: the acpi handle is NULL when we add the acpi
device for fixed power/sleep button. In such case it is still different
with the ACPI

>
> 4) acpi_walk_namespace(..., ACPI_ROOT_OBJECT, ...) doesn't actually
> visit the root node; it starts with the children. I consider
> this a bug. If it were ever fixed, we would probably call the
> callback with acpi_gbl_root_node, not ACPI_ROOT_OBJECT, so the
> root acpi_device handle would no longer be ACPI_ROOT_OBJECT.
When the ACPI_ROOT_OBJECT is passed to acpi_walk_namespace, then
it will start from acpi_gbl_root_node(this is changed in the function of
acpi_ns_walk_namespace).
>
> Bjorn
>
> > > +
> > > static LIST_HEAD(acpi_device_list);
> > > static LIST_HEAD(acpi_bus_id_list);
> > > DEFINE_MUTEX(acpi_device_lock);
> > > @@ -955,10 +957,12 @@ static void acpi_device_get_busid(struct acpi_device *device)
> > > * The device's Bus ID is simply the object name.
> > > * TBD: Shouldn't this value be unique (within the ACPI namespace)?
> > > */
> > > - switch (device->device_type) {
> > > - case ACPI_BUS_TYPE_SYSTEM:
> > > + if (ACPI_IS_ROOT_DEVICE(device)) {
> > > strcpy(device->pnp.bus_id, "ACPI");
> > > - break;
> > > + return;
> > > + }
> > > +
> > > + switch (device->device_type) {
> > > case ACPI_BUS_TYPE_POWER_BUTTON:
> > > strcpy(device->pnp.bus_id, "PWRF");
> > > break;
> > > @@ -1093,6 +1097,11 @@ static void acpi_device_set_id(struct acpi_device *device)
> > >
> > > switch (device->device_type) {
> > > case ACPI_BUS_TYPE_DEVICE:
> > > + if (ACPI_IS_ROOT_DEVICE(device)) {
> > > + hid = ACPI_SYSTEM_HID;
> > > + break;
> > > + }
> > > +
> > > status = acpi_get_object_info(device->handle, &info);
> > > if (ACPI_FAILURE(status)) {
> > > printk(KERN_ERR PREFIX "%s: Error reading device info\n", __func__);
> > > @@ -1129,9 +1138,6 @@ static void acpi_device_set_id(struct acpi_device *device)
> > > case ACPI_BUS_TYPE_PROCESSOR:
> > > hid = ACPI_PROCESSOR_OBJECT_HID;
> > > break;
> > > - case ACPI_BUS_TYPE_SYSTEM:
> > > - hid = ACPI_SYSTEM_HID;
> > > - break;
> > > case ACPI_BUS_TYPE_THERMAL:
> > > hid = ACPI_THERMAL_HID;
> > > break;
> > > @@ -1643,7 +1649,7 @@ int __init acpi_scan_init(void)
> > > * Create the root device in the bus's device tree
> > > */
> > > result = acpi_add_single_object(&acpi_root, ACPI_ROOT_OBJECT,
> > > - ACPI_BUS_TYPE_SYSTEM, &ops);
> > > + ACPI_BUS_TYPE_DEVICE, &ops);
> > > if (result)
> > > goto Done;
> > >
> > > diff --git a/include/acpi/acpi_bus.h b/include/acpi/acpi_bus.h
> > > index 8e39b3e..ef1cb23 100644
> > > --- a/include/acpi/acpi_bus.h
> > > +++ b/include/acpi/acpi_bus.h
> > > @@ -70,7 +70,6 @@ enum acpi_bus_device_type {
> > > ACPI_BUS_TYPE_POWER,
> > > ACPI_BUS_TYPE_PROCESSOR,
> > > ACPI_BUS_TYPE_THERMAL,
> > > - ACPI_BUS_TYPE_SYSTEM,
> > > ACPI_BUS_TYPE_POWER_BUTTON,
> > > ACPI_BUS_TYPE_SLEEP_BUTTON,
> > > ACPI_BUS_DEVICE_TYPE_COUNT
> > >
> > > --
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> >
> >
>
>