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Date:   Fri, 24 Mar 2023 08:51:53 +0200
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To:     David Gow <davidgow@google.com>
Cc:     Maxime Ripard <maxime@cerno.tech>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Brendan Higgins <brendan.higgins@linux.dev>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Heikki Krogerus <heikki.krogerus@linux.intel.com>,
        linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
        kunit-dev@googlegroups.com, Stephen Boyd <sboyd@kernel.org>,
        Jonathan Cameron <jic23@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 3/24/23 08:34, David Gow wrote:
> On Fri, 24 Mar 2023 at 14:11, Matti Vaittinen <mazziesaccount@gmail.com> wrote:
>>
>> On 3/23/23 18:36, Maxime Ripard wrote:
>>> On Thu, Mar 23, 2023 at 03:02:03PM +0200, Matti Vaittinen wrote:
>>>> On 3/23/23 14:29, Maxime Ripard wrote:
>>>>> On Thu, Mar 23, 2023 at 02:16:52PM +0200, Matti Vaittinen wrote:

>> Ok. Fair enough. Besides, if the root-device was sufficient - then I
>> would actually not see the need for a helper. People could in that case
>> directly use the root_device_register(). So, if helpers are provided
>> they should be backed up by a device with a bus then.
> 
> I think there is _some_ value in helpers even without a bus, but it's
> much more limited:
> - It's less confusing if KUnit test devices are using kunit labelled
> structs and functions.
> - Helpers could use KUnit's resource management API to ensure any
> device created is properly unregistered and removed when the test
> exits (particularly if it exits early due to, e.g., an assertion).

Ah. That's true. Being able to abort the test on error w/o being forced 
to do a clean-up dance for the dummy device would be convenient.

> I've played around implementing those with a proper struct
> kunit_device and the automatic cleanup on test failure, and thus far
> it -- like root_device_register -- works for all of the tests except
> the drm-test-managed one.
> 
> So if we really wanted to, we could use KUnit-specific helpers for
> just those tests which currently work with root_device_register(), but
> if we're going to try to implement a KUnit bus -- which I think is at
> least worth investigating -- I'd rather not either hold up otherwise
> good tests on helper development, or rush a helper out only to have to
> change it a lot when we see exactly what the bus implementation would
> look like.

It's easy for me to agree.

>> As I said, in my very specific IIO related test the test device does not
>> need a bus. Hence I'll drop the 'generic helpers' from this series.
>>
> 
> I think that sounds like a good strategy for now, and we can work on a
> set of 'generic helpers' which have an associated bus and struct
> kunit_device in the meantime. If we can continue to use
> root_device_register until those are ready, that'd be very convenient.

Would it be a tiny bit more acceptable if we did add a very simple:

#define kunit_root_device_register(name) root_device_register(name)
#define kunit_root_device_unregister(dev) root_device_unregister(dev)

to include/kunit/device.h (or somesuch)

This should help us later to at least spot the places where 
root_device_[un]register() is abused and (potentially mass-)covert them 
to use the proper helpers when they're available.

Yours,
	-- Matti


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

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