Re: [RFC v3 0/4] ACPI[CA]: fix ECDT EC probe ordering issues

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 10/13/22 18:53, Rafael J. Wysocki wrote:
> Hi Hans,
> 
> On Mon, Oct 3, 2022 at 4:42 PM Hans de Goede <hdegoede@redhat.com> wrote:
>>
>> Hi All,
>>
>> Here is v3 of my series fixing some ECDT EC probe ordering issues which
>> are causing issues om some laptops:
>>
>> https://bugzilla.kernel.org/show_bug.cgi?id=214899
>>
>> This is a RFC because fixing this requires some ACPICA changes which
>> obviously need to go upstream through the ACPICA project:
>> https://github.com/acpica/acpica/pull/786
> 
> I've just approved your pull request.

Thanks.

> Also, as soon as it gets merged, you can resubmit the series with a
> proper ACPICA  commit ID and I will be able to apply the patches right
> away then.

Will do.

Regards,

Hans



>> The problem this fixed is best described by the commit message of patch 4:
>>
>> ACPI-2.0 says that the EC OpRegion handler must be available immediately
>> (like the standard default OpRegion handlers):
>>
>> Quoting from the ACPI spec version 6.3: "6.5.4 _REG (Region) ...
>> 2. OSPM must make Embedded Controller operation regions, accessed via
>> the Embedded Controllers described in ECDT, available before executing
>> any control method. These operation regions may become inaccessible
>> after OSPM runs _REG(EmbeddedControl, 0)."
>>
>> So acpi_bus_init() calls acpi_ec_ecdt_probe(), which calls
>> acpi_install_address_space_handler() to install the EC's OpRegion
>> handler, early on.
>>
>> This not only installs the OpRegion handler, but also calls the EC's
>> _REG method. The _REG method call is a problem because it may rely on
>> initialization done by the _INI methods of one of the PCI / _SB root devs,
>> see for example: https://bugzilla.kernel.org/show_bug.cgi?id=214899 .
>>
>> Generally speaking _REG methods are executed when the ACPI-device they
>> are part of has a driver bound to it. Where as _INI methods must be
>> executed at table load time (according to the spec). The problem here
>> is that the early acpi_install_address_space_handler() call causes
>> the _REG handler to run too early.
>>
>> To allow fixing this the ACPICA code now allows to split the OpRegion
>> handler installation and the executing of _REG into 2 separate steps.
>>
>> This commit uses this ACPICA functionality to fix the EC probe ordering
>> by delaying the executing of _REG for ECDT described ECs till the matching
>> EC device in the DSDT gets parsed and acpi_ec_add() for it gets called.
>> This moves the calling of _REG for the EC on devices with an ECDT to
>> the same point in time where it is called on devices without an ECDT table.
>>
>> Changes in v3:
>> - Add a prep patch to fix an indentation issue in Linux' acpixf.h to fix
>>   the patch from ACPICA's script not applying
>> - Add 2 new functions to ACPICA for this instead of a flags argument
>>   1. acpi_install_address_space_handler_no_reg()
>>   2. acpi_execute_reg_methods()
>> - Add a patch to fix EC handler removal in the ECDT case
>>
>> From my pov this series is ready for merging once the ACPICA changes
>> are accepted.
> 
> I agree, please resubmit as soon as the upstream ACPICA pull request
> gets merged.
> 
> Thanks!
>