linux-kernel - Re: [PATCH net-next v5 05/13] net: pcs: add Renesas MII converter driver

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Date:   Fri, 20 May 2022 18:58:15 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Clément Léger <clement.leger@...tlin.com>
Cc:     "Russell King (Oracle)" <linux@...linux.org.uk>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Magnus Damm <magnus.damm@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Herve Codina <herve.codina@...tlin.com>,
        Miquèl Raynal <miquel.raynal@...tlin.com>,
        Milan Stevanovic <milan.stevanovic@...com>,
        Jimmy Lalande <jimmy.lalande@...com>,
        Pascal Eberhard <pascal.eberhard@...com>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v5 05/13] net: pcs: add Renesas MII converter
 driver

On Fri, May 20, 2022 at 05:49:34PM +0200, Clément Léger wrote:
> Le Fri, 20 May 2022 18:44:40 +0300,
> Vladimir Oltean <olteanv@...il.com> a écrit :
> 
> > On Fri, May 20, 2022 at 05:22:44PM +0200, Clément Léger wrote:
> > > Le Fri, 20 May 2022 11:49:14 +0300,
> > > Vladimir Oltean <olteanv@...il.com> a écrit :
> > >  
> > > > On Fri, May 20, 2022 at 09:52:41AM +0200, Clément Léger wrote:  
> > > > > > Also, as a request to unbind this driver would be disasterous to users,
> > > > > > I think you should set ".suppress_bind_attrs = true" to prevent the
> > > > > > sysfs bind/unbind facility being available. This doesn't completely
> > > > > > solve the problem.  
> > > > >
> > > > > Acked. What should I do to make it more robust ? Should I use a
> > > > > refcount per pdev and check that in the remove() callback to avoid
> > > > > removing the pdev if used ?  
> > > >
> > > > I wonder, if you call device_link_add(ds->dev, miic->dev, DL_FLAG_AUTOREMOVE_CONSUMER),
> > > > wouldn't that be enough to auto-unbind the DSA driver when the MII
> > > > converter driver unbinds?  
> > >
> > > I looiked at that a bit and I'm not sure how to achieve that cleanly. If
> > > I need to create this link, then I need to do it once for the dsa switch
> > > device. However, currently, the way I get the references to the MII
> > > converter are via the pcs-handle properties which are for each port.
> > >
> > > So, I'm not sure creating the link multiple times in miic_create() would
> > > be ok and also, I'm not sure how to create the link once without adding
> > > a specific property which points on the MII converter node and use that
> > > to create the link by adding miic_device_add_link() for instance.
> > >
> > > Do you have any preference ?  
> > 
> > The simplest (although not the most elegant) way would probably be to
> > pass the ds->dev as a second argument to miic_create(), and call
> > device_link_add() multiple times, letting all but the first call fail,
> > and ignoring the resulting NULL return code. Maybe others have a better idea.
> 
> That's indeed what I started to do although it's nasty to say the
> least... Moreover, the device_link_del() calls in miic_destroy() would
> have to be carefully made after all miic ports have been
> destroyed. Not sure this is going to be cleaner ! I'll try to think
> about it a bit more.

Wait... the whole idea with AUTOREMOVE_CONSUMER is that you _don't_
remove the device link.. you let it sit there such that the device core
knows there are other consumers it needs to remove when this driver
unbinds from the device.