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

Alexander Stein
2016-07-26T10:00:33Z

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.

Best regards,
Alexander