netdev - Re: [PATCH] dpaa_eth: fix usage as DSA master, try 3

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Date:   Mon, 25 May 2020 17:58:08 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     olteanv@...il.com
Cc:     andrew@...n.ch, f.fainelli@...il.com, vivien.didelot@...il.com,
        madalin.bucur@....nxp.com, netdev@...r.kernel.org
Subject: Re: [PATCH] dpaa_eth: fix usage as DSA master, try 3

From: Vladimir Oltean <olteanv@...il.com>
Date: Mon, 25 May 2020 00:22:51 +0300

> From: Vladimir Oltean <vladimir.oltean@....com>
> 
> The dpaa-eth driver probes on compatible string for the MAC node, and
> the fman/mac.c driver allocates a dpaa-ethernet platform device that
> triggers the probing of the dpaa-eth net device driver.
> 
> All of this is fine, but the problem is that the struct device of the
> dpaa_eth net_device is 2 parents away from the MAC which can be
> referenced via of_node. So of_find_net_device_by_node can't find it, and
> DSA switches won't be able to probe on top of FMan ports.
> 
> It would be a bit silly to modify a core function
> (of_find_net_device_by_node) to look for dev->parent->parent->of_node
> just for one driver. We're just 1 step away from implementing full
> recursion.
> 
> Actually there have already been at least 2 previous attempts to make
> this work:
> - Commit a1a50c8e4c24 ("fsl/man: Inherit parent device and of_node")
> - One or more of the patches in "[v3,0/6] adapt DPAA drivers for DSA":
>   https://patchwork.ozlabs.org/project/netdev/cover/1508178970-28945-1-git-send-email-madalin.bucur@nxp.com/
>   (I couldn't really figure out which one was supposed to solve the
>   problem and how).
> 
> Point being, it looks like this is still pretty much a problem today.
> On T1040, the /sys/class/net/eth0 symlink currently points to
> 
> ../../devices/platform/ffe000000.soc/ffe400000.fman/ffe4e6000.ethernet/dpaa-ethernet.0/net/eth0
> 
> which pretty much illustrates the problem. The closest of_node we've got
> is the "fsl,fman-memac" at /soc@...000000/fman@...000/ethernet@...00,
> which is what we'd like to be able to reference from DSA as host port.
> 
> For of_find_net_device_by_node to find the eth0 port, we would need the
> parent of the eth0 net_device to not be the "dpaa-ethernet" platform
> device, but to point 1 level higher, aka the "fsl,fman-memac" node
> directly. The new sysfs path would look like this:
> 
> ../../devices/platform/ffe000000.soc/ffe400000.fman/ffe4e6000.ethernet/net/eth0
> 
> And this is exactly what SET_NETDEV_DEV does. It sets the parent of the
> net_device. The new parent has an of_node associated with it, and
> of_dev_node_match already checks for the of_node of the device or of its
> parent.
> 
> Fixes: a1a50c8e4c24 ("fsl/man: Inherit parent device and of_node")
> Fixes: c6e26ea8c893 ("dpaa_eth: change device used")
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>

Applied and queued up for -stable, thanks.