Messages in this thread | | | Date | Fri, 10 May 2024 19:38:56 +0200 | Subject | Re: [PATCH v1 1/2] ACPI: EC: Install address space handler at the namespace root | From | Armin Wolf <> |
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Am 10.05.24 um 19:29 schrieb Andy Shevchenko:
> 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@gmx.de> wrote: >>>> 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 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.
Consider the following execution flow when the second EC probes:
1. acpi_install_address_space_handler_no_reg() fails with AE_ALREADY_EXISTS since the first EC has already installed a handler at ACPI_ROOT_OBJECT.
2. ec_install_handlers() fails with -ENODEV.
3. acpi_ec_setup() fails with -ENODEV.
4. acpi_ec_add() fails with -ENODEV.
5. Probe of seconds EC fails with -ENODEV.
This might cause problems if the second EC is supposed to for example handle EC query events. Of course if we only support a single EC, then this situation cannot happen.
>> 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.
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