Re: [PATCH 14/18] acpi: utils: Add function to fetch dependent acpi_devices

Dan Scally
2020-11-30T23:55:40Z

Hi Andy

On 30/11/2020 18:23, Andy Shevchenko wrote:
> On Mon, Nov 30, 2020 at 01:31:25PM +0000, Daniel Scally wrote:
>> ACPI devices declare themselves dependent on other devices via the _DEP
>> buffer. Fetching the dependee from dependent is a matter of parsing
>> _DEP, but currently there's no method to fetch dependent from dependee.
>> Add one, so we can parse sensors dependent on a PMIC from the PMIC's
>> acpi_driver.
> Do I understand correctly that it's an existing table provided by firmware that
> (ab)uses _DEP in such way? Note, the specification doesn't tell we may use it
> in this way, OTOH I don't remember if it strictly forbids such use.
>
> So, please elaborate in the commit message why you need this and pint out to
> the 6.5.8 "_DEP (Operation Region Dependencies)" which clearly says about
> OpRegions and that part already supported by ACPI in the Linux, if I'm not
> mistaken, need to refresh my memory.

Laurent's reply is good explanation, but for example see my Lenovo Miix
510's DSDT:

https://gist.githubusercontent.com/djrscally/e64d112180517352fa3392878b0f4a7d/raw/88b90b3ea4204fd7845257b6666fdade47cc2981/dsdt.dsl

Search OVTI2680 and OVTI5648 for the cameras. Both are dependent on
IN3472 devices (PMI0 and PMI1) which are the discrete type that we're
attempting to handle here.

>
> ...
>
>> + handle = adev->handle;
>> +
>> + if (!acpi_has_method(handle, "_DEP"))
>> + return 0;
>> +
>> + status = acpi_evaluate_reference(handle, "_DEP", NULL, &dep_handles);
>> + if (ACPI_FAILURE(status))
>> + return 0;
>> +
>> + for (i = 0; i < dep_handles.count; i++) {
>> + struct acpi_device_info *info;
>> +
>> + status = acpi_get_object_info(dep_handles.handles[i], &info);
>> + if (ACPI_FAILURE(status))
>> + continue;
>> +
>> + if (info->valid & ACPI_VALID_HID) {
>> + ret = acpi_bus_get_device(dep_handles.handles[i], &candidate);
>> + if (ret || !candidate) {
>> + kfree(info);
>> + continue;
>> + }
>> +
>> + if (candidate == dependee) {
>> + acpi_dev_put(candidate);
>> + kfree(info);
>> + return 1;
>> + }
>> +
>> + kfree(info);
>> + }
>> + }
> Can you utilize (by moving to here and export for ACPI layer the
> acpi_lpss_dep()?
oooh, yes, I think I can. Thank you!