linux-kernel - Re: [PATCH 3/8] kunit: Add test managed platform

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Date:   Wed, 15 Mar 2023 09:27:56 +0100
From:   Maxime Ripard <maxime@...no.tech>
To:     Stephen Boyd <sboyd@...nel.org>
Cc:     David Gow <davidgow@...gle.com>,
        Michael Turquette <mturquette@...libre.com>,
        linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org,
        patches@...ts.linux.dev,
        Brendan Higgins <brendan.higgins@...ux.dev>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Johannes Berg <johannes@...solutions.net>,
        Vincent Whitchurch <vincent.whitchurch@...s.com>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Christian Marangi <ansuelsmth@...il.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        devicetree@...r.kernel.org, linux-um@...ts.infradead.org,
        linux-kselftest@...r.kernel.org, kunit-dev@...glegroups.com
Subject: Re: [PATCH 3/8] kunit: Add test managed platform_device/driver APIs

Hi Stephen,

On Thu, Mar 09, 2023 at 03:31:15PM -0800, Stephen Boyd wrote:
> Quoting Maxime Ripard (2023-03-03 06:35:28)
> > On Fri, Mar 03, 2023 at 03:15:31PM +0800, David Gow wrote:
> > > 
> > > DRM has a similar thing already (albeit with a root_device, which is
> > > more common with KUnit tests generally):
> > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/drm/drm_kunit_helpers.h
> > > 
> > > But that's reasonably drm-specific, so it makes sense that it lives
> > > with DRM stuff. platform_device is a bit more generic.
> > 
> > I'd be very happy to get something from the core to address the same
> > thing.
> > 
> > I think the main thing we needed that isn't covered by this patch is we
> > wanted the device to be bound to its driver, so with probe being called
> > before calling the test (see 57a84a97bbda).
>
> Can you clarify? This patch makes a poor attempt at waiting for the
> platform driver to bind, but in reality it may not be bound by the time
> the driver register function returns.

The issue was that devm will only clean up the resources if the device
was bound to a driver so we were exhausting resources when running
dozens of test in a sequence.

The way I solved it for vc4 was to create a dumb platform driver with a
waitqueue, and wait for probe to be called.

I think we could make it more generic by allowing a pointer to a probe
function and calling it into our own probe implementation. What do you
think?

Maxime

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