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

Rafael J. Wysocki
2020-12-02T19:58:11Z

On Wed, Dec 2, 2020 at 8:39 PM Hans de Goede <hdegoede@redhat.com> wrote:
>
> Hi,
>
> On 12/2/20 2:49 PM, 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),
>
> That is fine. Thanks for taking those.
>
> > 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.
>
> Actually acpi_add_single_object() does depend on ACPI methods
> which may depend on opregions, that is the whole reason why
> this series is necessary. Otherwise we could just delay the
> binding of the driver based in dep_unmet which would be easier.
>
> Here are 2 actual examples of acpi_add_single_object() calling
> ACPI methods which may depend on opregions:
>
> 1. acpi_add_single_object() calls acpi_init_device_object() which
> calls acpi_set_pnp_ids() which fills a bunch if fields of
> struct acpi_device with info returned by the acpi_get_object_info()
> call.
>
> Specifically it stores the value returned by the _HID method in
> the acpi_device_pnp array for the device and that _HID method is
> actually the problem in the example device which started this
> series. The _HID method of the bluetooth device reads 2 GPIOs
> to get a hw-id (0-3) and then translates the hwid to a _HID
> string. If the GPIO opregion's handlers have not registered yet
> then the reading of the GPIOs is correctly skipped, and hwid
> 0 is assumed, which is wrong in this case.
>
> 2. I've also seen examples where _STA depends on GPIOs in a similar
> manner; and acpi_add_single_object() calls acpi_bus_get_power_flags()
> which calls acpi_bus_init_power() which calls acpi_device_is_present()
> which depends on _STA results.

Well, this means that there is a bug in acpi_bus_attach() which
shouldn't call acpi_bus_init_power() which has been called already.

And it all means that either deferring acpi_add_single_object() is
needed and so there need to be 2 passes in acpi_bus_attach() overall,
or acpi_add_single_object() needs to avoid calling methods that may
depend on supplied opregions. I guess the latter is rather
unrealistic, so the only practical choice is the former.

However, I still don't think that the extra list of "dependent
devices" is needed.