linux-kernel - Re: [PATCH v5 1/8] drivers: kunit: Generic helpers for test device creation

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Message-ID: <f1390b01-c77e-3f67-acfc-7434f87d4856@gmail.com>
Date:   Thu, 23 Mar 2023 13:00:27 +0200
From:   Matti Vaittinen <mazziesaccount@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     "Vaittinen, Matti" <Matti.Vaittinen@...rohmeurope.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Brendan Higgins <brendan.higgins@...ux.dev>,
        David Gow <davidgow@...gle.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "kunit-dev@...glegroups.com" <kunit-dev@...glegroups.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Maxime Ripard <maxime@...no.tech>,
        Jonathan Cameron <jic23@...nel.org>,
        "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>
Subject: Re: [PATCH v5 1/8] drivers: kunit: Generic helpers for test device
 creation

On 3/23/23 12:27, Greg Kroah-Hartman wrote:
> On Thu, Mar 23, 2023 at 12:01:15PM +0200, Matti Vaittinen wrote:
>> 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;
>>          }
> 
> Yes as it wants to "split" a device up into smaller devices.  So make a
> real device that it can hang off of.

Yep. This is what led me to the root_device_register()... :rolleyes: And 
seein the root-device alone could do what I need - adding auxiliary 
device on top of it just for the sake of adding one seems a bit of an 
over-engineering to me :)

>> 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...
> 
> I think it is worth it as the driver core has no tests.  So it obviously
> must be correct, right?  :)

Doh. Greg, I hate you :) How could one argue with something like this? I 
think I will submit the v6 with the root_device_register() due to the 
aux-device requiring it in any case. I know that will end up to your 
table still as IIO is going through your hands anyways.

I will however take a look at what Maxime said about devm unwinding not 
being done w/o a bus because I think I saw the unwinding done in these 
IIO tests even when using the root_device_register() 
root_device_unregister(). If the unwinding really is not done, then I 
will come back to this auxiliary device rehearsal

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

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