On 06/30/2016 06:59 AM, Jonathan Cameron wrote:

On 30 June 2016 04:47:25 BST, Guenter Roeck [off-list ref] wrote:

quoted

On Tue, Jun 28, 2016 at 10:18:17AM +0200, Quentin Schulz wrote:

quoted

iio_channel_get_all returns -ENODEV when it cannot find either

phandles and

quoted

properties in the Device Tree or channels whose consumer_dev_name

matches

quoted

iio_hwmon in iio_map_list. The iio_map_list is filled in by iio

drivers

quoted

which might be probed after iio_hwmon.

It is better to defer the probe of iio_hwmon if such error is

returned by

quoted

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 <redacted>
---
  drivers/hwmon/iio_hwmon.c | 5 ++++-
  1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/hwmon/iio_hwmon.c b/drivers/hwmon/iio_hwmon.c
index b550ba5..c0da4d9 100644
--- a/drivers/hwmon/iio_hwmon.c
+++ b/drivers/hwmon/iio_hwmon.c

@@ -73,8 +73,11 @@ static int iio_hwmon_probe(struct platform_device

*pdev)

quoted

  		name = dev->of_node->name;

  	channels = iio_channel_get_all(dev);
-	if (IS_ERR(channels))
+	if (IS_ERR(channels)) {
+		if (PTR_ERR(channels) == -ENODEV)
+			return -EPROBE_DEFER;

The problem, as I see it, is with iio, which should return
-EPROBE_DEFER
in this situation.

Agreed. New fangled stuff this deferred probing :)

quoted

We can not convert -ENODEV to -EPROBE_DEFER without risking that the
channels are _really_ not there, which would result in endless
"deferred"
messages.

Hmm not entirely sure how we prevent that happening wherever it is done..

Outch. Better at the source, though. I didn't look at the iio code recently,
but can you detect the defer situation at least with devicetree ?

For non-devicetree situations, the only option I can think of would be
to replace the module initcall with a later initcall. That should solve
the problem if both iio_hwmon and and underlying drivers are built
into the kernel. If iio_hwmon is modular, the only real option I can
see is to make sure that all drivers it needs are loaded first.

Does this make sense ?

Guenter

quoted

Guenter

quoted

  		return PTR_ERR(channels);
+	}

  	st = devm_kzalloc(dev, sizeof(*st), GFP_KERNEL);
  	if (st == NULL) {

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