netdev - Re: [PATCH net 2/2] dpaa_eth: fix usage as DSA master, try 4

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Date:   Tue, 16 Jun 2020 14:51:31 +0000
From:   Joakim Tjernlund <Joakim.Tjernlund@...inera.com>
To:     "olteanv@...il.com" <olteanv@...il.com>,
        "davem@...emloft.net" <davem@...emloft.net>
CC:     "vivien.didelot@...il.com" <vivien.didelot@...il.com>,
        "madalin.bucur@....nxp.com" <madalin.bucur@....nxp.com>,
        "fido_max@...ox.ru" <fido_max@...ox.ru>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "andrew@...n.ch" <andrew@...n.ch>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net 2/2] dpaa_eth: fix usage as DSA master, try 4

On Tue, 2020-06-16 at 17:41 +0300, Vladimir Oltean wrote:
> 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.
> 
> On T1040, the /sys/class/net/eth0 symlink currently points to:
> 
> ../../devices/platform/ffe000000.soc/ffe400000.fman/ffe4e6000.ethernet/net/eth0

Just want to point out that on 4.19.x, the above patch still exists:
cd /sys
find -name eth0
./devices/platform/ffe000000.soc/ffe400000.fman/ffe4e6000.ethernet/net/eth0
./class/net/eth

> 
> 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/dpaa-ethernet.0/net/eth0
> 
> Actually this has worked before, through the SET_NETDEV_DEV mechanism,
> which sets the parent of the net_device as the parent of the platform
> device. But the device which was set as sysfs parent was inadvertently
> changed through commit 060ad66f9795 ("dpaa_eth: change DMA device"),
> which did not take into consideration the effect it would have upon
> of_find_net_device_by_node. So restore the old sysfs parent to make that
> work correctly.
> 
> Fixes: 060ad66f9795 ("dpaa_eth: change DMA device")
> 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 c4416a5f8816..2972244e6eb0 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
>