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 18:41:48 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Armin Wolf <W_Armin@....de>
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

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.