Re: [v6 08/14] iio: imu: add Bosch Sensortec BNO055 core driver

From: Andrea Merello <andrea.merello@gmail.com>
To: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Andrea Merello <Andrea.Merello@iit.it>,
	Jonathan Cameron <jic23@kernel.org>,
	Mauro Carvalho Chehab <mchehab+huawei@kernel.org>,
	linux-iio <linux-iio@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	devicetree <devicetree@vger.kernel.org>,
	Lars-Peter Clausen <lars@metafoo.de>,
	Rob Herring <robh+dt@kernel.org>,
	Matt Ranostay <matt.ranostay@konsulko.com>,
	Alexandru Ardelean <ardeleanalex@gmail.com>,
	jmondi <jacopo@jmondi.org>
Subject: Re: [v6 08/14] iio: imu: add Bosch Sensortec BNO055 core driver
Date: Tue, 14 Jun 2022 17:27:32 +0200	[thread overview]
Message-ID: <CAN8YU5PDoAaFcp83NMBZLcMJ99FWOxDc9DXLJthE9uNkK-izHg@mail.gmail.com> (raw)
In-Reply-To: <CAHp75Vd_w1WOp9ntbNqxtuuVXi0kMGbX=OZ7cioNxoh2yUa1ag@mail.gmail.com>

Il giorno mar 14 giu 2022 alle ore 17:11 Andy Shevchenko
<andy.shevchenko@gmail.com> ha scritto:
>
> On Tue, Jun 14, 2022 at 2:15 PM Andrea Merello <Andrea.Merello@iit.it> wrote:
>
> ...
>
> > >> >> +       devm_add_action_or_reset(priv->dev, bno055_debugfs_remove, priv->debugfs);
> > >> >
> > >> >Shouldn't we report the potential error here? It's not directly
> > >> >related to debugfs, but something which is not directly related.
> > >>
> > >> The error eventually comes out from something that has nothing to do with debugs per se (i.e. the devm stuff), but it will only affect debugfs indeed.
> > >>
> > >> Assuming that we don't want to make the whole driver fail in case debugfs stuff fails (see last part of the comment above debugfs_create_file() implementation), and given that the devm_add_action_or_reset(), should indeed "reset" in case of failure (i.e.  we should be in a clean situation anyway), I would say it should be OK not to propagate the error and let things go on.
> > >
> > >As I said, it's not directly related to debugfs. Here is the resource
> > >leak possible or bad things happen if you probe the driver, that fails
> > >to add this call for removal, remove it, and try to insert again, in
> > >such case the debugfs will be stale.
> >
> > Hum, I would say this shouldn't ever happen: AFAICS devm_add_action_or_reset() is a wrapper around devm_add_action() and it's purpose is exactly to add a check for failure; devm_add_action_or_reset() immediately invokes the action handler in case devm_add_action() fails. IOW in case of failure to add the devm stuff, the debugfs file is removed immediately and it shouldn't cause any mess with next times probe()s; just the driver will go on without the debugfs file being here.
> >
> > I think this is the point of using devm_add_action_or_reset() instead of dev_add_action()  indeed, or am I missing something?
>
> Reading that code again and I think you are right, so dev_warn() will
> be sufficient to show that we fail. OTOH, what is the point of adding
> a resource for the failed debugfs call?

Ah, you are right here: I'll make the call to
devm_add_action_or_reset() conditional to success of
debugfs_create_file(). In case any of the two fails we can also warn
the user.

> --
> With Best Regards,
> Andy Shevchenko