Re: [PATCH v3 1/4] hwmon: iio_hwmon: delay probing with late_initcall

[Quentin Schulz <quentin.schulz@free-electrons.com>]

On 26/07/2016 12:00, Alexander Stein wrote:
> On Tuesday 26 July 2016 11:33:59, Quentin Schulz wrote:
>> On 26/07/2016 11:05, Alexander Stein wrote:
>>> On Tuesday 26 July 2016 10:24:48, Quentin Schulz wrote:
>>>> On 26/07/2016 10:21, Alexander Stein wrote:
>>>>> On Tuesday 26 July 2016 09:43:44, Quentin Schulz wrote:
>>>>>> iio_channel_get_all returns -ENODEV when it cannot find either phandles
>>>>>> and
>>>>>> properties in the Device Tree or channels whose consumer_dev_name
>>>>>> matches
>>>>>> iio_hwmon in iio_map_list. The iio_map_list is filled in by iio drivers
>>>>>> which might be probed after iio_hwmon.
>>>>>
>>>>> Would it work if iio_channel_get_all returning ENODEV is used for
>>>>> returning
>>>>> EPROBE_DEFER in iio_channel_get_all? Using late initcalls for
>>>>> driver/device
>>>>> dependencies seems not right for me at this place.
>>>>
>>>> Then what if the iio_channel_get_all is called outside of the probe of a
>>>> driver? We'll have to change the error code, things we are apparently
>>>> trying to avoid (see v2 patches' discussions).
>>>
>>> Maybe I didn't express my idea enough. I don't want to change the behavior
>>> of iio_channel_get_all at all. Just the result evaluation of
>>> iio_channel_get_all in iio_hwmon_probe. I have something link the patch
>>> below in mind.
>>>
>>> Best regards,
>>> Alexander
>>> ---
>>> diff --git a/drivers/hwmon/iio_hwmon.c b/drivers/hwmon/iio_hwmon.c
>>> index b550ba5..e32d150 100644
>>> --- a/drivers/hwmon/iio_hwmon.c
>>> +++ b/drivers/hwmon/iio_hwmon.c
>>> @@ -73,8 +73,12 @@ static int iio_hwmon_probe(struct platform_device
>>> *pdev)
>>>
>>>                 name = dev->of_node->name;
>>>         
>>>         channels = iio_channel_get_all(dev);
>>>
>>> -       if (IS_ERR(channels))
>>> -               return PTR_ERR(channels);
>>> +       if (IS_ERR(channels)) {
>>> +               if (PTR_ERR(channels) == -ENODEV)
>>> +                       return -EPROBE_DEFER;
>>> +               else
>>> +                       return PTR_ERR(channels);
>>> +       }
>>>
>>>         st = devm_kzalloc(dev, sizeof(*st), GFP_KERNEL);
>>>         if (st == NULL) {
>>
>> Indeed, I misunderstood what you told me.
>>
>> Actually, the patch you proposed is part of my v1
>> (https://lkml.org/lkml/2016/6/28/203) and v2
>> (https://lkml.org/lkml/2016/7/15/215).
>> Jonathan and Guenter didn't really like the idea of changing the -ENODEV
>> in -EPROBE_DEFER.
> 
> Thanks for the links.
> 
>> What I thought you were proposing was to change the -ENODEV return code
>> inside iio_channel_get_all. This cannot be an option since the function
>> might be called outside of a probe (it is not yet, but might be in the
>> future?).
> 
> AFAICS this is a helper function not knowing about device probing itself. And 
> it should stay at that.
> 
>> Of what I understood, two possibilities are then possible (proposed
>> either by Guenter or Jonathan): either rework the iio framework to
>> register iio map array earlier or to use late_initcall instead of init
>> for the driver consuming the iio channels.
> 
> Interestingly using this problem would not arise due to module dependencies. 
> But using late_initcall would mean this needs to be done on any driver using 
> iio channels? I would rather keep those consumers simple.

This would mean this needs to be done in any driver *using iio_map
array* to get iio channels. The other way of getting iio channels is
using properties in the Device Tree so no need for late_initcall in that
case.

Quentin