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Date:   Thu, 23 Mar 2023 12:01:15 +0200
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To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Vaittinen, Matti" <Matti.Vaittinen@fi.rohmeurope.com>
Cc:     "Rafael J. Wysocki" <rafael@kernel.org>,
        Brendan Higgins <brendan.higgins@linux.dev>,
        David Gow <davidgow@google.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Heikki Krogerus <heikki.krogerus@linux.intel.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-kselftest@vger.kernel.org" <linux-kselftest@vger.kernel.org>,
        "kunit-dev@googlegroups.com" <kunit-dev@googlegroups.com>,
        Stephen Boyd <sboyd@kernel.org>,
        Maxime Ripard <maxime@cerno.tech>,
        Jonathan Cameron <jic23@kernel.org>,
        "linux-iio@vger.kernel.org" <linux-iio@vger.kernel.org>
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From:   Matti Vaittinen <mazziesaccount@gmail.com>
Subject: Re: [PATCH v5 1/8] drivers: kunit: Generic helpers for test device
 creation
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On 3/23/23 10:58, Greg Kroah-Hartman wrote:
> On Thu, Mar 23, 2023 at 07:17:40AM +0000, Vaittinen, Matti wrote:
>> On 3/22/23 20:57, Greg Kroah-Hartman wrote:
>>> On Wed, Mar 22, 2023 at 03:48:00PM +0200, Matti Vaittinen wrote:
>>>> Hi Greg,
>>>>
>>>> Thanks for looking at this.
>>>>
>>>> On 3/22/23 14:07, Greg Kroah-Hartman wrote:
>>>>> On Wed, Mar 22, 2023 at 11:05:55AM +0200, Matti Vaittinen wrote:

>>>> The biggest thing for me is that I don't like the idea of creating own 'test
>>>> device' in <add subsystem here> while we already have some in DRM (or
>>>> others). Thus, I do see value in adding generic helpers for supporting
>>>> running KUnit tests on devm_* APIs. Hence it'd be good to have _some_
>>>> support for it.
>>>
>>> I agree, let's use a virtual device and a virtual bus (you can use the
>>> auxbus code for this as that's all there for this type of thing)
>>
>> Hm. The auxiliary_devices require parent. What would be the best way to
>> deal with that in KUnit tests?
> 
> If you use NULL as the parent, it goes into the root.

As far as I read this is not the case with auxiliary devices. Judging 
the docs they were intended to be representing some part of a (parent) 
device. I see the auxiliary_device_init() has explicit check for parent 
being populated:

int auxiliary_device_init(struct auxiliary_device *auxdev)
{
         struct device *dev = &auxdev->dev;

         if (!dev->parent) {
                 pr_err("auxiliary_device has a NULL dev->parent\n");
                 return -EINVAL;
         }

As I wrote in another mail, I thought of using a root_device for this 
IIO test as was suggested by David. To tell the truth, implementing a 
kunit bus device is starting to feel a bit overwhelming... I started 
just adding a driver for a light sensor, ended up adding a helper for 
IIO gain-time-scale conversions and I am slightly reluctant to going the 
extra-extra mile of adding some UT infrastructure in the context of this 
driver work...

Well, let's see. Maybe I change my mind after a good night's sleep :)

Yours,
	-- Matti

-- 
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland

~~ When things go utterly wrong vim users can always type :help! ~~