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

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Date:   Thu, 23 Mar 2023 15:02:03 +0200
From:   Matti Vaittinen <mazziesaccount@...il.com>
To:     Maxime Ripard <maxime@...no.tech>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Matti Vaittinen <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-kselftest@...r.kernel.org,
        kunit-dev@...glegroups.com, Stephen Boyd <sboyd@...nel.org>,
        Jonathan Cameron <jic23@...nel.org>, linux-iio@...r.kernel.org
Subject: Re: [PATCH v5 1/8] drivers: kunit: Generic helpers for test device
 creation

On 3/23/23 14:29, Maxime Ripard wrote:
> On Thu, Mar 23, 2023 at 02:16:52PM +0200, Matti Vaittinen wrote:
> 
> This is the description of what was happening:
> https://lore.kernel.org/dri-devel/20221117165311.vovrc7usy4efiytl@houat/
Thanks Maxime. Do I read this correcty. The devm_ unwinding not being 
done when root_device_register() is used is not because 
root_device_unregister() would not trigger the unwinding - but rather 
because DRM code on top of this device keeps the refcount increased?

If this is the case, then it sounds like a DRM specific issue to me. 
Whether it is a feature or bug is beyond my knowledge. Still, I would 
not say using the root_device_[un]register() in generic code is not 
feasible - unless all other subsytems have similar refcount handling.

Sure thing using root_device_register() root_device_unregister() in DRM 
does not work as such. This, however, does not mean the generic kunit 
helpers should use platform_devices to force unwinding?

Well, It's almost the best season for ice-fishing in Finland so opening 
a can of worms is not that bad, right? :)

Thanks for the education people! I did learn a thing or two Today.

Yours,
	-- Matti

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

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