linux-kernel - Re: [PATCH v2 08/11] driver core: fw_devlink: Make cycle detection more robust

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Message-ID: <Y9e09qUa9CDxHFcb@smile.fi.intel.com>
Date:   Mon, 30 Jan 2023 14:15:50 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Cristian Marussi <cristian.marussi@....com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>, Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Magnus Damm <magnus.damm@...il.com>,
        Len Brown <lenb@...nel.org>,
        Daniel Scally <djrscally@...il.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Tony Lindgren <tony@...mide.com>,
        Linux Kernel Functional Testing <lkft@...aro.org>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        Abel Vesa <abel.vesa@...aro.org>,
        Alexander Stein <alexander.stein@...tq-group.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        John Stultz <jstultz@...gle.com>,
        Doug Anderson <dianders@...omium.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Maxim Kiselev <bigunclemax@...il.com>,
        Maxim Kochetkov <fido_max@...ox.ru>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Luca Weiss <luca.weiss@...rphone.com>,
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        Martin Kepplinger <martin.kepplinger@...i.sm>,
        Jean-Philippe Brucker <jpb@...nel.org>,
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        devicetree@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        linux-acpi@...r.kernel.org
Subject: Re: [PATCH v2 08/11] driver core: fw_devlink: Make cycle detection
 more robust

On Fri, Jan 27, 2023 at 11:34:28PM -0800, Saravana Kannan wrote:
> On Fri, Jan 27, 2023 at 1:43 AM Andy Shevchenko
> <andriy.shevchenko@...ux.intel.com> wrote:
> > On Thu, Jan 26, 2023 at 04:11:35PM -0800, Saravana Kannan wrote:

...

> Lol, you are the king of nit picks :)

Not always, only when it comes with something else.

...

> > > + * Return true if one or more cycles were found. Otherwise, return false.
> >
> > Return:
> 
> I'm following the rest of the function docs in this file.

Okay, it makes sense. We will need to address them all.

> > (you may run `kernel-doc -v ...` to see all warnings)
> 
> Hmmm I ran it on the patch file and it didn't give me anything useful.
> Running it on the whole file is just a lot of lines to dig through.

The function description missing Return section. Something like this
I can get from the kernel doc without it.

...

> > > +static bool __fw_devlink_relax_cycles(struct device *con,
> > > +                              struct fwnode_handle *sup_handle)
> > > +{
> > > +     struct fwnode_link *link;
> > > +     struct device_link *dev_link;
> >
> > > +     struct device *sup_dev = NULL, *par_dev = NULL;
> >
> > You can put it the first line since it's long enough.
> 
> Wait, is that a style guideline to have the longer lines first?

No, but it's easier to read.

> > But why do you need sup_dev assignment?
> 
> Defensive programming I suppose. I can see this function being
> refactored in the future where a goto out; is inserted before sup_dev
> is assigned. And then the put_device(sup_dev) at "out" will end up
> operating on some junk value and causing memory corruption.

We don't need to be defensive here. Moreover, it's harder and easy to make
a mistake with predefined values (it's actually better NOT to define anything
qr at least define as closest to its user as possible, so you want miss the
compiler warnings as I believe you run your compiler with `make W=1 ...`, and
if not, I highly recommend to get this habit).

...

> > > +     sup_dev = get_dev_from_fwnode(sup_handle);
> > > +
> >
> > I would put it closer to the condition:
> >
> > > +     /* Termination condition. */
> > > +     if (sup_dev == con) {
> >
> >         /* Get supplier device and check for termination condition */
> >         sup_dev = get_dev_from_fwnode(sup_handle);
> >         if (sup_dev == con) {
> 
> I put it the way it is because sup_dev is used for more than just
> checking for termination condition.

Yes, but still it's better to see what you are actually checking.

> > > +             ret = true;
> > > +             goto out;
> > > +     }

...

> > > +             if (__fw_devlink_relax_cycles(con,
> > > +                                           dev_link->supplier->fwnode)) {
> >
> > Keep it on one line.
> 
> It'll make it > 80. Is this some recent change about allowing > 80
> cols? I'm leaving it as is for now.

Is it a problem? Do you have any tool that complains about it?

-- 
With Best Regards,
Andy Shevchenko