On Mon, Jan 16, 2017 at 12:01:02PM -0800, Florian Fainelli wrote:
> On 01/15/2017 11:16 AM, Andrew Lunn wrote:
> >>> What exactly is the relationship between these devices (a ascii-art tree
> >>> or sysfs tree output might be nice) so I can try to understand what is
> >>> going on here.
> >
> > Hi Greg, Florian
> >
> > A few diagrams and trees which might help understand what is going on.
> >
> > The first diagram comes from the 2008 patch which added all this code:
> >
> > +-----------+ +-----------+
> > | | RGMII | |
> > | +-------+ +------ 1000baseT MDI ("WAN")
> > | | | 6-port +------ 1000baseT MDI ("LAN1")
> > | CPU | | ethernet +------ 1000baseT MDI ("LAN2")
> > | |MIImgmt| switch +------ 1000baseT MDI ("LAN3")
> > | +-------+ w/5 PHYs +------ 1000baseT MDI ("LAN4")
> > | | | |
> > +-----------+ +-----------+
> >
> > We have an ethernet switch and a host CPU. The switch is connected to
> > the CPU in two different ways. RGMII allows us to get Ethernet frames
> > from the CPU into the switch. MIImgmt, is the management bus normally
> > used for Ethernet PHYs, but Marvell switches also use it for Managing
> > switches.
> >
> > The diagram above is the simplest setup. You can have multiple
> > Ethernet switches, connected together via switch ports. Each switch
> > has its own MIImgmt connect to the CPU, but there is only one RGMII
> > link.
> >
> > When this code was designed back in 2008, it was decided to represent
> > this is a platform device, and it has a platform_data, which i have
> > slightly edited to keep it simple:
> >
> > struct dsa_platform_data {
> > /*
> > * Reference to a Linux network interface that connects
> > * to the root switch chip of the tree.
> > */
> > struct device *netdev;
> >
> > /*
> > * Info structs describing each of the switch chips
> > * connected via this network interface.
> > */
> > int nr_chips;
> > struct dsa_chip_data *chip;
> > };
> >
> > This netdev is the CPU side of the RGMII interface.
> >
> > Each switch has a dsa_chip_data, again edited:
> >
> > struct dsa_chip_data {
> > /*
> > * How to access the switch configuration registers.
> > */
> > struct device *host_dev;
> > int sw_addr;
> > ...
> > }
> >
> > The host_dev is the CPU side of the MIImgmt, and we have the address
> > the switch is using on the bus.
> >
> > During probe of this platform device, we need to get from the
> > struct device *netdev to a struct net_device *dev.
> >
> > So the code looks in the device net class to find the device
> >
> > | | | |-- f1074000.ethernet
> > | | | | |-- deferred_probe
> > | | | | |-- driver -> ../../../../../bus/platform/drivers/mvneta
> > | | | | |-- driver_override
> > | | | | |-- modalias
> > | | | | |-- net
> > | | | | | `-- eth1
> > | | | | | |-- addr_assign_type
> > | | | | | |-- address
> > | | | | | |-- addr_len
> > | | | | | |-- broadcast
> > | | | | | |-- carrier
> > | | | | | |-- carrier_changes
> > | | | | | |-- deferred_probe
> > | | | | | |-- device -> ../../../f1074000.ethernet
> >
> > and then use container_of() to get the net_device.
> >
> > Similarly, the code needs to get from struct device *host_dev to a struct
> > mii_bus *.
> >
> > | | | |-- f1072004.mdio
> > | | | | |-- deferred_probe
> > | | | | |-- driver -> ../../../../../bus/platform/drivers/orion-mdio
> > | | | | |-- driver_override
> > | | | | |-- mdio_bus
> > | | | | | `-- f1072004.mdio-mi
> > | | | | | |-- deferred_probe
> > | | | | | |-- device -> ../../../f1072004.mdio
> >
>
> Thanks Andrew! Greg, does that make it clearer how these devices
> references are used, do you still think the way this is done is wrong,
> too cautious, or valid?
I'm still not sold on it, I think there is something odd here with your
use/assumptions of the driver model. Give me a few days to catch up
with other stuff to respond back please...
thanks,
greg k-h
