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

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Message-ID: <ed5c1761-bdc7-df9c-96c8-998e83c49c4c@free-electrons.com>
Date:	Tue, 26 Jul 2016 11:33:59 +0200
From:	Quentin Schulz <quentin.schulz@...e-electrons.com>
To:	Alexander Stein <alexander.stein@...tec-electronic.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 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.

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?).

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.

Thanks,
Quentin