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

Rafael J. Wysocki
2020-12-02T15:53:01Z

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.

---
drivers/acpi/scan.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 52 insertions(+), 3 deletions(-)

Index: linux-pm/drivers/acpi/scan.c
===================================================================
--- linux-pm.orig/drivers/acpi/scan.c
+++ linux-pm/drivers/acpi/scan.c
@@ -1961,12 +1961,50 @@ 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;
+
+ /*
+ * We check for _ADR here to avoid deferring the adding of the following:
+ * 1. PCI devices
+ * 2. ACPI nodes describing USB ports
+ * Note checking for _ADR catches more then just these cases ...
+ */
+ if (adev->pnp.type.bus_address)
+ return false;
+
+ 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);

@@ -2013,12 +2051,23 @@ 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;