Message-ID: <ZBx/mO/z3t3dQCAx@smile.fi.intel.com>
Date:   Thu, 23 Mar 2023 18:34:32 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Daniel Scally <djrscally@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Jakub Kicinski <kuba@...nel.org>, linux-acpi@...r.kernel.org,
        netdev@...r.kernel.org, Paolo Abeni <pabeni@...hat.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Vladimir Oltean <olteanv@...il.com>
Subject: Re: [PATCH RFC net-next 3/7] net: dsa: use fwnode_get_phy_mode() to
 get phy interface mode

On Thu, Mar 23, 2023 at 04:18:15PM +0000, Russell King (Oracle) wrote:
> On Thu, Mar 23, 2023 at 03:23:12PM +0000, Russell King (Oracle) wrote:
> > On Thu, Mar 23, 2023 at 05:00:08PM +0200, Andy Shevchenko wrote:
> > > On Thu, Mar 23, 2023 at 02:49:01PM +0000, Russell King (Oracle) wrote:
> > > > On Thu, Mar 23, 2023 at 04:38:29PM +0200, Andy Shevchenko wrote:
> > > > > Do you modify its content on the fly?
> > > > 
> > > > Do you want to litter code with casts to get rid of the const?
> > > > 
> > > > > For fwnode as a basic object type we want to reduce the scope of the possible
> > > > > modifications. If you don't modify and APIs you call do not require non-const
> > > > > object, use const for fwnode.
> > > > 
> > > > Let's start here. We pass this fwnode to fwnode_get_phy_mode():
> > > > 
> > > > include/linux/property.h:int fwnode_get_phy_mode(struct fwnode_handle *fwnode);
> > > > 
> > > > Does fwnode_get_phy_mode() alter the contents of the fwnode? Probably
> > > > not, but it doesn't take a const pointer. Therefore, to declare my
> > > > fwnode as const, I'd need to cast the const-ness away before calling
> > > > this.
> > > 
> > > So, fix the fwnode_get_phy_mode(). Is it a problem?
> > 
> > No, I refuse. That's for a different patch set.
> > 
> > > > Then there's phylink_create(). Same problem.
> > > 
> > > So, fix that. Is it a problem?
> > 
> > No for the same reason.
> > 
> > > > So NAK to this const - until such time that we have a concerted effort
> > > > to making functions we call which do not modify the "fwnode" argument
> > > > constify that argument. Otherwise it's just rediculously crazy to
> > > > declare a variable const only to then litter the code with casts to get
> > > > rid of it at every call site.
> > > > 
> > > > Please do a bit of research before making suggestions. Thanks.
> > > 
> > > So, MAK to your patch. You can fix that, and you know that.
> > 
> > Sorry, I don't accept your NAK. While you have a valid point about
> > these things being const, that is not the fault of this patch series,
> > and is something that should be addressed separately.
> > 
> > The lack of const-ness that has been there for quite some time is no
> > reason to NAK a patch that has nothing to do with this.
> 
> To illustrate how rediculous this is:

It's not. But does it make difference?

> $ git grep 'struct fwnode_handle \*.*='
> 
> gives 134 instances. Of those, only five are const, which means 129
> aren't. So I question - why are you singling mine out for what appears
> to be special treatment.
> 
> 
> Let's look at other parts of the fwnode API.
> 
> void __iomem *fwnode_iomap(struct fwnode_handle *fwnode, int index);
> 
> Does that modify the fwnode it was passed? It calls:
> 
>         void __iomem *(*iomap)(struct fwnode_handle *fwnode, int index);
> 
> in struct fwnode_operations, so that would need to be made const as well.
> The only implementation of that which I can find is of_fwnode_iomap()
> which uses to_of_node() on that, which casts away the const-ness. So
> this would be a candidate to making const.

Correct.

> bool fwnode_is_ancestor_of(struct fwnode_handle *ancestor, struct fwnode_handle *child);
> 
> I'd be surprised if that modifies either of those fwnodes.

It does. Now your time to be surprised.

> It seems
> to use fwnode_for_each_parent_node() from the child, which passes
> "child" to fwnode_get_parent(), which itself is const. Therefore, it
> seems there's no reason not to make "child" const. "ancestor" can
> also be made const since it's only being used for pointer-compares.

All getters return _different_ fwnode which is not const due to modification
of the _returned_ fwnode.

Do a bit of investigation, please. Thanks.

> unsigned int fwnode_graph_get_endpoint_count(struct fwnode_handle *fwnode,
>                                              unsigned long flags);
> 
> Similar story with this, although it uses
> fwnode_graph_for_each_endpoint(), which seems to mean that "fwnode"
> can also be const.

Correct.

> My point is that there are several things in the fwnode API that
> should be made const but that aren't, but which should likely be
> fixed before requiring const-ness of those fwnode_handle
> declarations in people's code.

OK.

I started doing something about this as you may easily check with `git log`.
Now, instead of playing a good citizen of the community you are trying to
diminish the others' asks.

I think the further continuation of this discussion doesn't make much sense.
But thank you for your opinion.

-- 
With Best Regards,
Andy Shevchenko

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