Re: [PATCH 0/7] ACPI: scan: Split root scanning into 2 steps

Rafael J. Wysocki
2020-12-02T19:47:01Z

On Wednesday, December 2, 2020 4:51:59 PM CET Rafael J. Wysocki wrote:
> On Wednesday, December 2, 2020 2:49:17 PM CET Rafael J. Wysocki wrote:
> > On Sat, Nov 21, 2020 at 9:30 PM Hans de Goede <hdegoede@redhat.com> wrote:
> > >
> > > Hi Rafael,
> > >
> > > A while ago (almost 2 years ago) I discussed an issue with you about
> > > some devices, where some of the methods used during device-addition
> > > (such as _HID) may rely on OpRegions of other devices:
> > >
> > > https://www.spinics.net/lists/linux-acpi/msg86303.html
> > >
> > > An example of this is the Acer Switch 10E SW3-016 model. The _HID method
> > > of the ACPI node for the UART attached Bluetooth, reads GPIOs to detect
> > > the installed wifi chip and update the _HID for the Bluetooth's ACPI node
> > > accordingly. The current ACPI scan code calls _HID before the GPIO
> > > controller's OpRegions are available, leading to the wrong _HID being
> > > used and Bluetooth not working.
> > >
> > > Last week I bought a second hand Acer device, not knowing it was this
> > > exact model. Since I now have access to affected hardware I decided to
> > > take a shot at fixing this.
> > >
> > > In the discussion you suggested to split the acpi_bus_scan of the root
> > > into 2 steps, first scan devices with an empty _DEP, putting other
> > > acpi_handle-s on a list of deferred devices and then in step 2 scan the
> > > rest.
> > >
> > > I'm happy to report that, at least on the affected device, this works
> > > nicely. While working on this I came up with a less drastic way to
> > > deal with this. As you will see in patch 4 of this series, I decided
> > > to first add a more KISS method of deciding which devices to defer
> > > to the second scan step by matching by HID. This has the disadvantage
> > > of not being a generic solution. But it has the advantage of being a
> > > solution which does not potentially regress other devices.
> > >
> > > Then in patch 5 I actually do add the option to defer or not based on
> > > _DEP being empty. I've put this behind a kernel commandline option as
> > > I'm not sure we should do this everywhere by default. At least no without
> > > a lot more testing.
> > >
> > > Patch 6 fixes an issue with patch 5 which causes battery devices to stop
> > > working.
> > >
> > > And patch 7 adds some extra HIDs to the list of HIDs which should be
> > > ignored when checking if the _DEP list is empty from Linux' pov, iow
> > > some extra HIDs which Linux does not bind to.
> > >
> > > Please let me know what you think about this patch-set. I would be happy
> > > to see just patches 1-4 merged.
> >
> > I took patches 1 and 2, because IMO they are generally useful (I
> > rewrote the changelogs to avoid mentioning the rest of the series
> > though), but I have some reservations regarding the rest.
> >
> > First off, I'm not really sure if failing acpi_add_single_object() for
> > devices with missing dependencies is a good idea. IIRC there is
> > nothing in there that should depend on any opregions supplied by the
> > other devices, so it should be safe to allow it to complete. That, in
> > turn, will allow the flags in struct acpi_device to be used to mark
> > the "deferred" devices without allocating more memory.
> >
> > Next, in theory, devices with dependencies may also appear during
> > hotplug, so it would be prudent to handle that on every invocation of
> > acpi_bus_scan() and not just when it runs for the root object.
> >
> > So my approach would be to allow the first namespace walk in
> > acpi_bus_scan() to complete, change acpi_bus_attach() to optionally
> > skip the devices with missing dependencies and return a result
> > indicating whether or not it has set flags.visited for any devices and
> > run it in a loop on the "root" device object until it says that no new
> > devices have been "attached".
> >
> > Let me cut a prototype patch for that and get back to you.
>
> Maybe something like the patch below (untested). I borrowed a few items from
> your patches, hopefully not a problem.
>
> The multiple passes idea would require using a static variable which would
> be slightly inelegant, so this assumes that two passes should be sufficient.
>

An update.

This one has been lightly tested, but it doesn't make any practical difference
on the system where it was run AFAICS.

I found a missing ! in acpi_scan_should_defer_attach() and then realized that
looking for _ADR wasn't really necessary, because _ADR devices should not be
affected by this in a meaningful way anyway (scan handlers and ACPI drivers
match on the _HID and/or _CID basis and the status check/power up in
__acpi_bus_attach() should be skipped for them, because they may be "glued"
to their "physical" counterparts before this code runs even - looks like a
bug).

---
drivers/acpi/scan.c | 47 ++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 44 insertions(+), 3 deletions(-)

Index: linux-pm/drivers/acpi/scan.c
===================================================================
--- linux-pm.orig/drivers/acpi/scan.c
+++ linux-pm/drivers/acpi/scan.c
@@ -1979,12 +1979,42 @@ static int acpi_scan_attach_handler(stru
return ret;
}

-static void acpi_bus_attach(struct acpi_device *device)
+/*
+ * List of IDs for which we defer adding them to the second pass of the
+ * scanning, because some of their methods used during addition depend on
+ * OpRegions registered by the drivers for other ACPI devices.
+ */
+static const struct acpi_device_id acpi_defer_attach_ids[] = {
+ { "BCM2E5B", 0 }, /* Acer SW3-016 bluetooth vs GPIO OpRegs */
+ {"", 0},
+};
+
+static bool acpi_scan_should_defer_attach(struct acpi_device *adev)
+{
+ if (!acpi_match_device_ids(adev, acpi_defer_attach_ids))
+ return true;
+
+ return adev->dep_unmet > 0;
+}
+
+static void __acpi_bus_attach(struct acpi_device *device, bool first_pass)
{
struct acpi_device *child;
acpi_handle ejd;
int ret;

+ if (first_pass) {
+ if (acpi_scan_should_defer_attach(device))
+ return;
+ } else if (device->flags.visited) {
+ /*
+ * This is not the first pass in the given scan and the device
+ * has been "attached" already, so get to the children right
+ * away.
+ */
+ goto ok;
+ }
+
if (ACPI_SUCCESS(acpi_bus_get_ejd(device->handle, &ejd)))
register_dock_dependent_device(device, ejd);

@@ -2031,12 +2061,23 @@ static void acpi_bus_attach(struct acpi_

ok:
list_for_each_entry(child, &device->children, node)
- acpi_bus_attach(child);
+ __acpi_bus_attach(child, first_pass);

- if (device->handler && device->handler->hotplug.notify_online)
+ if (first_pass && device->handler &&
+ device->handler->hotplug.notify_online)
device->handler->hotplug.notify_online(device);
}

+static void acpi_bus_attach(struct acpi_device *device)
+{
+ /*
+ * Assume two passes to be sufficient to satisfy all of the operation
+ * region dependencies.
+ */
+ __acpi_bus_attach(device, true);
+ __acpi_bus_attach(device, false);
+}
+
void acpi_walk_dep_device_list(acpi_handle handle)
{
struct acpi_dep_data *dep, *tmp;