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

From: Daniel Scally
Date: Thu Jan 21 2021 - 16:08:02 EST

On 21/01/2021 18:08, Rafael J. Wysocki wrote:
> On Thu, Jan 21, 2021 at 5:34 PM Daniel Scally <djrscally@xxxxxxxxx> wrote:
>> On 21/01/2021 14:39, Rafael J. Wysocki wrote:
>>> On Thu, Jan 21, 2021 at 1:04 PM Daniel Scally <djrscally@xxxxxxxxx> wrote:
>>>> 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;
>>>> }
>>> That would work I think, but would it be practical to modify
>>> acpi_walk_dep_device_list() so that it runs a callback for every
>>> consumer found instead of or in addition to the "delete from the list
>>> and free the entry" operation?
>> I think that this would work fine, if that's the way you want to go.
>> We'd just need to move everything inside the if (dep->supplier ==
>> handle) block to a new callback, and for my purposes I think also add a
>> way to stop parsing the list from the callback (so like have the
>> callbacks return int and stop parsing on a non-zero return). Do you want
>> to expose that ability to pass a callback outside of ACPI?
> Yes.
>> Or just export helpers to call each of the callbacks (one to fetch the next
>> dependent device, one to decrement the unmet dependencies counter)
> If you can run a callback for every matching entry, you don't really
> need to have a callback to return the next matching entry. You can do
> stuff for all of them in one go

Well it my case it's more to return a pointer to the dep->consumer's
acpi_device for a matching entry, so my idea was where there's multiple
dependents you could use this as an iterator...but it could just be
extended to that if needed later; I don't actually need to do it right now.

> note that it probably is not a good
> idea to run the callback under the lock, so the for loop currently in
> there is not really suitable for that

No problem;  I'll tweak that then

>> Otherwise, I'd just need to update the 5 users of that function either
>> to use the new helper or else to also pass the decrement dependencies
>> callback.
> Or have a wrapper around it passing the decrement dependencies
> callback for the "typical" users.

Yeah that's what I mean by helper; I'll do that then; thanks