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

[Alexander Stein <alexander.stein@systec-electronic.com>]

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