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Date:   Thu, 23 Mar 2023 11:27:09 +0100
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Matti Vaittinen <mazziesaccount@gmail.com>
Cc:     "Vaittinen, Matti" <Matti.Vaittinen@fi.rohmeurope.com>,
        "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>
Subject: Re: [PATCH v5 1/8] drivers: kunit: Generic helpers for test device
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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.

> 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?  :)

thanks,

greg k-h