Re: [PATCH net-next v3 06/10] net: dsa: Migrate to device_find_class()

On Thu, Jan 19, 2017 at 05:30:13PM +0100, Greg KH wrote:

On Thu, Jan 19, 2017 at 03:53:15PM +0100, Andrew Lunn wrote:

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struct dsa_platform_data {
        /*
         * Reference to a Linux network interface that connects
         * to the root switch chip of the tree.
         */
        struct device   *netdev;

This I think is the oddest thing, why do you need to have the "root
switch" here?  You seem to have dropped the next value in this
structure:
	struct net_device *of_netdev;

We are implementing platform_data for devices which don't support
device tree. When using OF, we don't have any of these issues. We can
go straight to the device.

It is a bit convoluted, but look at
arch/arm/mach-orion5x/rd88f5181l-ge-setup.c. It defines the start of
the dsa_platform_data in that file. It then gets passed through
common.c: orion5x_eth_switch_init() to 
arch/arm/plat-orion/common.c:orion_ge00_switch_init() :

void __init orion_ge00_switch_init(struct dsa_platform_data *d)
{
        int i;

        d->netdev = &orion_ge00.dev;
        for (i = 0; i < d->nr_chips; i++)
                d->chip[i].host_dev = &orion_ge_mvmdio.dev;

        platform_device_register_data(NULL, "dsa", 0, d, sizeof(d));
}

Where we have

static struct platform_device orion_ge00 = {
        .name           = MV643XX_ETH_NAME,
        .id             = 0,
        .num_resources  = 1,
        .resource       = orion_ge00_resources,
        .dev            = {
                .coherent_dma_mask      = DMA_BIT_MASK(32),
        },
};

So this is the platform device for the Ethernet device. We cannot go
to the net_device, because it does not exist until this Ethernet
platform device is instantiated.

Ok, fine, but why isn't the ethernet device a child of this platform
device?  Why is it floating around somewhere else?  You don't see that
happening for other devices.

The ethernet device is not a child of the DSA device.  I'm going to
send a mail I've had queued up for a few hours redoing Andrew's
ASCII art, because I think that's what's causing the confusion here,
provided I haven't discarded it.

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