linux-kernel - Re: [PATCH v1 1/2] ACPI: EC: Install address space handler at the namespace root

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

Am 10.05.24 um 18:41 schrieb Rafael J. Wysocki:

> On Fri, May 10, 2024 at 6:10 PM Armin Wolf <W_Armin@....de> wrote:
>> Am 10.05.24 um 16:03 schrieb Rafael J. Wysocki:
>>
>>> From: Rafael J. Wysocki <rafael.j.wysocki@...el.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 address
>>> space:
>>>
>>>    ACPI Error: No handler for Region [ECSI] (000000007b8176ee) [EmbeddedControl] (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 multiple
>> 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 than
one ACPI EC device.

This patch would prevent any ACPI ECs other than the first one from probing,
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