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Re: [v2,1/4] hwmon: iio_hwmon: defer probe when no channel is found

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Hi Guenter,

On Sat, Jul 16, 2016 at 10:00:13AM -0700, Guenter Roeck wrote:
> On Fri, Jul 15, 2016 at 11:59:11AM +0200, 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.
> > 
> > It is better to defer the probe of iio_hwmon if such error is returned by
> > iio_channel_get_all in order to let a chance to iio drivers to expose
> > channels in iio_map_list.
> > 
> > Signed-off-by: Quentin Schulz <quentin.schulz@free-electrons.com>
> > ---
> > 
> > No modifications for this patch since we did not settled for a solution.
> > What should we do?
> > 
> AFAICS the only thing we can do is to replace module_platform_driver() with
> its explicitly coded variant, and to use use late_initcall() instead of
> module_init().

I thought this kind of changes to the driver init time were
discouraged these days?

> Anything else would result in endless probe deferrals if there are
> no channels.

Well, technically, not endless. AFAIK, the kernel only retries when a
new driver is probed, which should hopefully settle down rather
quickly.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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[PATCH v2 0/4] add support for Allwinner SoCs ADC Quentin Schulz <quentin.schulz@free-electrons.com> - 2016-07-15 12:10 +0200
  [PATCH v2 3/4] mfd: add support for Allwinner SoCs ADC Quentin Schulz <quentin.schulz@free-electrons.com> - 2016-07-15 12:10 +0200
    Re: [PATCH v2 3/4] mfd: add support for Allwinner SoCs ADC Maxime Ripard <maxime.ripard@free-electrons.com> - 2016-07-18 15:10 +0200
      Re: [PATCH v2 3/4] mfd: add support for Allwinner SoCs ADC Quentin Schulz <quentin.schulz@free-electrons.com> - 2016-07-19 14:10 +0200
    Re: [PATCH v2 3/4] mfd: add support for Allwinner SoCs ADC Jonathan Cameron <jic23@kernel.org> - 2016-07-19 07:40 +0200
      Re: [PATCH v2 3/4] mfd: add support for Allwinner SoCs ADC Lee Jones <lee.jones@linaro.org> - 2016-07-19 09:40 +0200
        Re: [PATCH v2 3/4] mfd: add support for Allwinner SoCs ADC Jonathan Cameron <jic23@kernel.org> - 2016-07-20 17:10 +0200
          Re: [PATCH v2 3/4] mfd: add support for Allwinner SoCs ADC Lee Jones <lee.jones@linaro.org> - 2016-07-21 14:20 +0200
            Re: [PATCH v2 3/4] mfd: add support for Allwinner SoCs ADC Maxime Ripard <maxime.ripard@free-electrons.com> - 2016-07-21 22:10 +0200
              Re: [PATCH v2 3/4] mfd: add support for Allwinner SoCs ADC Lee Jones <lee.jones@linaro.org> - 2016-07-22 16:00 +0200
                Re: [PATCH v2 3/4] mfd: add support for Allwinner SoCs ADC Jonathan Cameron <jic23@kernel.org> - 2016-07-23 13:00 +0200
                Re: [PATCH v2 3/4] mfd: add support for Allwinner SoCs ADC Maxime Ripard <maxime.ripard@free-electrons.com> - 2016-07-25 12:00 +0200
      Re: [PATCH v2 3/4] mfd: add support for Allwinner SoCs ADC Quentin Schulz <quentin.schulz@free-electrons.com> - 2016-07-19 10:40 +0200
  [PATCH v2 1/4] hwmon: iio_hwmon: defer probe when no channel is found Quentin Schulz <quentin.schulz@free-electrons.com> - 2016-07-15 12:10 +0200
    Re: [v2,1/4] hwmon: iio_hwmon: defer probe when no channel is found Guenter Roeck <linux@roeck-us.net> - 2016-07-16 19:10 +0200
      Re: [v2,1/4] hwmon: iio_hwmon: defer probe when no channel is found Maxime Ripard <maxime.ripard@free-electrons.com> - 2016-07-18 12:10 +0200
        Re: [v2,1/4] hwmon: iio_hwmon: defer probe when no channel is found Guenter Roeck <linux@roeck-us.net> - 2016-07-18 15:30 +0200
  [PATCH v2 4/4] hwmon: iio: add label for channels read by iio_hwmon Quentin Schulz <quentin.schulz@free-electrons.com> - 2016-07-15 12:10 +0200
    Re: [PATCH v2 4/4] hwmon: iio: add label for channels read by  iio_hwmon Guenter Roeck <linux@roeck-us.net> - 2016-07-15 16:10 +0200
      Re: [PATCH v2 4/4] hwmon: iio: add label for channels read by  iio_hwmon Quentin Schulz <quentin.schulz@free-electrons.com> - 2016-07-15 16:40 +0200
        Re: [PATCH v2 4/4] hwmon: iio: add label for channels read by  iio_hwmon Guenter Roeck <linux@roeck-us.net> - 2016-07-16 05:00 +0200
    Re: [PATCH v2 4/4] hwmon: iio: add label for channels read by  iio_hwmon Jonathan Cameron <jic23@kernel.org> - 2016-07-19 07:40 +0200
      Re: [PATCH v2 4/4] hwmon: iio: add label for channels read by  iio_hwmon Quentin Schulz <quentin.schulz@free-electrons.com> - 2016-07-19 09:00 +0200
        Re: [PATCH v2 4/4] hwmon: iio: add label for channels read by  iio_hwmon Jonathan Cameron <jic23@kernel.org> - 2016-07-20 16:50 +0200

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