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

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Message-Id: <20200524212251.3311546-1-olteanv@gmail.com>
Date:   Mon, 25 May 2020 00:22:51 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     davem@...emloft.net
Cc:     andrew@...n.ch, f.fainelli@...il.com, vivien.didelot@...il.com,
        madalin.bucur@....nxp.com, netdev@...r.kernel.org
Subject: [PATCH] dpaa_eth: fix usage as DSA master, try 3

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>
---
 drivers/net/ethernet/freescale/dpaa/dpaa_eth.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
index 2cd1f8efdfa3..6bfa7575af94 100644
--- a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
+++ b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
@@ -2914,7 +2914,7 @@ static int dpaa_eth_probe(struct platform_device *pdev)
 	}

 	/* Do this here, so we can be verbose early */
-	SET_NETDEV_DEV(net_dev, dev);
+	SET_NETDEV_DEV(net_dev, dev->parent);
 	dev_set_drvdata(dev, net_dev);

 	priv = netdev_priv(net_dev);
-- 
2.25.1