Re: [PATCH v2 2/7] acpi: utils: Add function to fetch dependent acpi_devices

[Daniel Scally]

On 19/01/2021 13:15, Rafael J. Wysocki wrote:
> On Mon, Jan 18, 2021 at 9:51 PM Daniel Scally <djrscally@xxxxxxxxx> wrote:
>> On 18/01/2021 16:14, Rafael J. Wysocki wrote:
>>> On Mon, Jan 18, 2021 at 1:37 AM Daniel Scally <djrscally@xxxxxxxxx> wrote:
>>>> In some ACPI tables we encounter, devices use the _DEP method to assert
>>>> a dependence on other ACPI devices as opposed to the OpRegions that the
>>>> specification intends. We need to be able to find those devices "from"
>>>> the dependee, so add a function to parse all ACPI Devices and check if
>>>> the include the handle of the dependee device in their _DEP buffer.
>>> What exactly do you need this for?
>> So, in our DSDT we have devices with _HID INT3472, plus sensors which
>> refer to those INT3472's in their _DEP method. The driver binds to the
>> INT3472 device, we need to find the sensors dependent on them.
>>
> Well, this is an interesting concept. :-)
>
> Why does _DEP need to be used for that?  Isn't there any other way to
> look up the dependent sensors?


If there is, I'm not aware of it, I don't see a reference to the sensor
in the INT3472 device (named "PMI0", with the corresponding sensor being
"CAM0") in DSDT  [1]

>>> Would it be practical to look up the suppliers in acpi_dep_list instead?
>>>
>>> Note that supplier drivers may remove entries from there, but does
>>> that matter for your use case?
>> Ah - that may work, yes. Thank you, let me test that.
> Even if that doesn't work right away, but it can be made work, I would
> very much prefer that to the driver parsing _DEP for every device in
> the namespace by itself.


Alright; I haven't looked too closely yet, but I think an iterator over
acpi_dep_list exported from the ACPI subsystem would also work in a
pretty similar way to the function introduced in this patch does,
without much work


[1]
https://gist.githubusercontent.com/djrscally/e64d112180517352fa3392878b0f4a7d/raw/88b90b3ea4204fd7845257b6666fdade47cc2981/dsdt.dsl