Received-SPF: pass (google.com: domain of linux-kernel+bounces-110202-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:4601:e00::3 as permitted sender) client-ip=2604:1380:4601:e00::3;
Date: Thu, 21 Mar 2024 16:10:34 +0100
From: Andrew Lunn <andrew@lunn.ch>
To: Josua Mayer <josua@solid-run.com>
Cc: Jiri Pirko <jiri@resnulli.us>, Florian Fainelli <f.fainelli@gmail.com>,
	Vladimir Oltean <olteanv@gmail.com>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] net: dsa: mv88e6xxx: add warning for truncated mdio bus
 id
Message-ID: <37af3d75-68dd-41ea-b97e-7ce020ebaa8c@lunn.ch>
References: <20240320-mv88e6xxx-truncate-busid-v1-1-cface50b2efb@solid-run.com>
 <Zfrt_dlYvBzlxull@nanopsycho>
 <c76c95af-71cb-4eb6-b3af-846ae318d18d@solid-run.com>
 <793649ff-990c-46f0-9132-bc6e95fcb94f@lunn.ch>
 <78211827-7ffb-41ac-bd78-a2641bca7c00@solid-run.com>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <78211827-7ffb-41ac-bd78-a2641bca7c00@solid-run.com>

On Thu, Mar 21, 2024 at 10:26:54AM +0000, Josua Mayer wrote:
> Am 20.03.24 um 19:57 schrieb Andrew Lunn:
> >> With separators ('!') we have:
> >> cp0!config-space@f2000000!mdio@12a200!ethernet-switch@4!mdio
> >> cp0!config-space@f2000000!mdio@12a200!ethernet-switch@4!mdio-external
> >> Truncated to MII_BUS_ID_SIZE:
> >> cp0!config-space@f2000000!mdio@12a200!ethernet-switch@4!mdi
> >> cp0!config-space@f2000000!mdio@12a200!ethernet-switch@4!mdi
> > This has been made worse by the DT maintainers wanting
> > ethernet-switch@4, not switch@4. And i guess config-space was also
> > something shorter in the past.
> >
> > I think your idea of cropping from the beginning, not the end, is in
> > general a good solution. However, is there any danger of
> >
> > cp0!config-space@f2000000!mdio@12a200!ethernet-switch@4!mdio-external
> >
> > and
> >
> > cp1!config-space@f2000000!mdio@12a200!ethernet-switch@4!mdio-external
> Since these will appear as links in /sys/bus/mdio_bus/devices,
> this danger exists.
> If the prefix is too similar, we can run into duplicates also when
> cropping from the front.
> 
> So we could crop at the front and reduce likelihood of this situation,
> but (imo) should still print a warning since it is not working as intended.

The problem with a warning is, what do you tell people who ask how to
fix the warning? Hack your device tree to short the node names?

A warning is best done when there is something which can be done to
fix the problem. If it is not fixable, it is just noise.

> > Another option would be if the name needs to be truncated, use the
> > fallback as if there was no np:
> >
> >                 bus->name = "mv88e6xxx SMI";
> >                 snprintf(bus->id, MII_BUS_ID_SIZE, "mv88e6xxx-%d", index++);
> >
> > That at least gives you unique names.
> This ensures a unique suffix within a branch of device-tree.
> It could still collide with same structure on a cp1 or cp2.

static int mv88e6xxx_mdio_register(struct mv88e6xxx_chip *chip,
                                   struct device_node *np,
                                   bool external)
{
        static int index;
        struct mv88e6xxx_mdio_bus *mdio_bus;
        struct mii_bus *bus;
        int err;

index is static, so it is simply a counter. So you should get the
names mv88e6xxx-0, mv88e6xxx-1, mv88e6xxx-2, mv88e6xxx-3...

	Andrew