Am 10.05.24 um 19:40 schrieb Mario Limonciello:
On 5/10/2024 12:29, Andy Shevchenko wrote:
On Fri, May 10, 2024 at 06:52:41PM +0200, Armin Wolf wrote:
Am 10.05.24 um 18:41 schrieb Rafael J. Wysocki:
On Fri, May 10, 2024 at 6:10 PM Armin Wolf <W_Armin@xxxxxx> wrote:
Am 10.05.24 um 16:03 schrieb Rafael J. Wysocki:
From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
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.
The specification is clear about this case in the "ACPI Embedded
Controller
Interface Specification":
"The ACPI standard supports multiple embedded controllers in a system,
each with its own resources. Each embedded controller has a flat
byte-addressable I/O space, currently defined as 256 bytes."
However, I haven't checked deeper, so it might be a leftover in the
documentation.
The OperationRegion() has no reference to the EC (or in general,
device) which
we need to speak to. The only possibility to declare OpRegion() for
the second+
EC is to use vendor specific RegionSpace, AFAIU. So, even if ACPI
specification
supports 2+ ECs, it doesn't support OpRegion():s for them under the same
RegionSpace.
That said, the commit message might be extended to summarize this,
but at
the same time I see no way how this series can break anything even in
2+ ECs
environments.
It's deviating from the patch, but in practice /why/ would you even
want to have a design with two ECs? In general that is going to mean
a much more complex state machine with synchronizing the interaction
between both of them and the host.
Understanding the benefit of such a design might make it easier to
hypothesize impacts.
I am not saying that such designs would make sense, it was a theoretical question only.
Maybe we can just add a small note to the Linux ACPI documentation saying that we only
support a single EC device?
Thanks,
Armin Wolf
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.
