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

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Message-ID: <ZBrvhfX/NNrJefgt@kroah.com>
Date:   Wed, 22 Mar 2023 13:07:33 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Matti Vaittinen <mazziesaccount@...il.com>
Cc:     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>,
        Maxime Ripard <maxime@...no.tech>,
        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 Wed, Mar 22, 2023 at 11:05:55AM +0200, Matti Vaittinen wrote:
> --- /dev/null
> +++ b/drivers/base/test/test_kunit_device.c
> @@ -0,0 +1,83 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * These helpers have been extracted from drm test code at
> + * drm_kunit_helpers.c which was authored by
> + * Maxime Ripard <maxime@...no.tech>
> + */
> +
> +#include <linux/device.h>
> +#include <linux/platform_device.h>
> +
> +#include <kunit/platform_device.h>
> +
> +#define KUNIT_DEVICE_NAME	"test-kunit-mock-device"
> +
> +static int fake_probe(struct platform_device *pdev)

Please do not abuse platform devices and drivers for things that are not
actually platform devices and drivers.

> +{
> +	return 0;
> +}
> +
> +static int fake_remove(struct platform_device *pdev)
> +{
> +	return 0;
> +}
> +
> +static struct platform_driver fake_platform_driver = {
> +	.probe	= fake_probe,
> +	.remove	= fake_remove,
> +	.driver = {
> +		.name	= KUNIT_DEVICE_NAME,
> +	},
> +};

Why do you need this fake platform driver at all?

Why not just use a virtual device?

> +
> +/**
> + * test_kunit_helper_alloc_device - Allocate a mock device for a KUnit test
> + * @test: The test context object
> + *
> + * This allocates a fake struct &device to create a mock for a KUnit
> + * test. The device will also be bound to a fake driver. It will thus be
> + * able to leverage the usual infrastructure and most notably the
> + * device-managed resources just like a "real" device.

What specific "usual infrastructure" are you wanting to access here?

And again, if you want a fake device, make a virtual one, by just
calling device_create().

Or are you wanting to do "more" with that device pointer than
device_create() can give you?

Again, please do not abuse the platform device infrastructure for things
it was never ment to do (i.e. create fake devices that are not really a
platform device.)

thanks,

greg k-h