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

[Daniel Scally]

On 21/01/2021 11:58, Rafael J. Wysocki wrote:
> On Thu, Jan 21, 2021 at 10:47 AM Daniel Scally <djrscally@xxxxxxxxx> wrote:
>> Hi Rafael
>>
>> 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?
>>>
>>>>> 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.
>>
>> This does work; do you prefer it in scan.c, or in utils.c (in which case
>> with acpi_dep_list declared as external var in internal.h)?
> Let's put it in scan.c for now, because there is the lock protecting
> the list in there too.
>
> How do you want to implement this?  Something like "walk the list and
> run a callback for the matching entries" or do you have something else
> in mind?


Something like this (though with a mutex_lock()). It could be simplified
by dropping the prev stuff, but we have seen INT3472 devices with
multiple sensors declaring themselves dependent on the same device


struct acpi_device *
acpi_dev_get_next_dependent_dev(struct acpi_device *supplier,
                struct acpi_device *prev)
{
    struct acpi_dep_data *dep;
    struct acpi_device *adev;
    int ret;

    if (!supplier)
        return ERR_PTR(-EINVAL);

    if (prev) {
        /*
         * We need to find the previous device in the list, so we know
         * where to start iterating from.
         */
        list_for_each_entry(dep, &acpi_dep_list, node)
            if (dep->consumer == prev->handle &&
                dep->supplier == supplier->handle)
                break;

        dep = list_next_entry(dep, node);
    } else {
        dep = list_first_entry(&acpi_dep_list, struct acpi_dep_data,
                       node);
    }


    list_for_each_entry_from(dep, &acpi_dep_list, node) {
        if (dep->supplier == supplier->handle) {
            ret = acpi_bus_get_device(dep->consumer, &adev);
            if (ret)
                return ERR_PTR(ret);

            return adev;
        }
    }

    return NULL;
}