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

[Daniel Scally]

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? Or just
export helpers to call each of the callbacks (one to fetch the next
dependent device, one to decrement the unmet dependencies counter)


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.