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

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