linux-kernel - Re: [PATCH net-next v3 06/10] net: dsa: Migrate to device_find

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Message-ID: <20170119163548.GG27312@n2100.armlinux.org.uk>
Date:   Thu, 19 Jan 2017 16:35:48 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        netdev@...r.kernel.org, Jason Cooper <jason@...edaemon.net>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Gregory Clement <gregory.clement@...e-electrons.com>,
        Vivien Didelot <vivien.didelot@...oirfairelinux.com>,
        "David S. Miller" <davem@...emloft.net>,
        "moderated list:ARM SUB-ARCHITECTURES" 
        <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: 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:
> > > > > 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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