linux-kernel - Re: [PATCH v3 1/4] hwmon: iio_hwmon: delay probing with late

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Date:	Tue, 26 Jul 2016 11:05:49 +0200
From:	Alexander Stein <alexander.stein@...tec-electronic.com>
To:	Quentin Schulz <quentin.schulz@...e-electrons.com>
Cc:	linux-kernel@...r.kernel.org, jdelvare@...e.com,
	linux@...ck-us.net, jic23@...nel.org, knaack.h@....de,
	lars@...afoo.de, pmeerw@...erw.net,
	maxime.ripard@...e-electrons.com, wens@...e.org,
	lee.jones@...aro.org, linux-hwmon@...r.kernel.org,
	linux-iio@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	thomas.petazzoni@...e-electrons.com,
	antoine.tenart@...e-electrons.com
Subject: Re: [PATCH v3 1/4] hwmon: iio_hwmon: delay probing with late_initcall

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) {