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Date: Fri, 10 May 2024 18:52:41 +0200
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Subject: Re: [PATCH v1 1/2] ACPI: EC: Install address space handler at the
 namespace root
To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
 Linux ACPI <linux-acpi@vger.kernel.org>, LKML
 <linux-kernel@vger.kernel.org>,
 Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
 Hans de Goede <hdegoede@redhat.com>,
 Mario Limonciello <mario.limonciello@amd.com>,
 Heikki Krogerus <heikki.krogerus@linux.intel.com>
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From: Armin Wolf <W_Armin@gmx.de>
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Am 10.05.24 um 18:41 schrieb Rafael J. Wysocki:

> On Fri, May 10, 2024 at 6:10=E2=80=AFPM Armin Wolf <W_Armin@gmx.de> wrot=
e:
>> Am 10.05.24 um 16:03 schrieb Rafael J. Wysocki:
>>
>>> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>>>
>>> It is reported that _DSM evaluation fails in ucsi_acpi_dsm() on Lenovo
>>> IdeaPad Pro 5 due to a missing address space handler for the EC addres=
s
>>> space:
>>>
>>>    ACPI Error: No handler for Region [ECSI] (000000007b8176ee) [Embedd=
edControl] (20230628/evregion-130)
>>>
>>> This happens because the EC driver only registers the EC address space
>>> handler for operation regions defined in the EC device scope of the
>>> ACPI namespace while the operation region being accessed by the _DSM
>>> in question is located beyond that scope.
>>>
>>> To address this, modify the ACPI EC driver to install the EC address
>>> space handler at the root of the ACPI namespace.
>>>
>>> Note that this change is consistent with some examples in the ACPI
>>> specification in which EC operation regions located outside the EC
>>> device scope are used (for example, see Section 9.17.15 in ACPI 6.5),
>>> so the current behavior of the EC driver is arguably questionable.
>> Hi,
>>
>> the patch itself looks good to me, but i wonder what happens if multipl=
e
>> ACPI EC devices are present. How would we handle such a situation?
> I'm wondering if this is a theoretical question or do you have any
> existing or planned systems in mind?
>
> ec_read(), ec_write() and ec_transaction() use only the first EC that
> has been found anyway.

Its a theoretical question, i do not know of any systems which have more t=
han
one ACPI EC device.

This patch would prevent any ACPI ECs other than the first one from probin=
g,
since they would fail to register their address space handler.
I am just curious if/how we want to handle such situations.

Thanks,
Armin Wolf