[U-Boot-Users] PATCH: add support for MII-connected ethernet switch for IPX42x

[Ben Warren <bwarren@qstreams.com>]

Michael Schwingen wrote:
> Jean-Christophe PLAGNIOL-VILLARD wrote:
>   
>> 	If you have a switch between your phy and your cpu the speed and
>> 	the duplex must be specified by the phy driver.
>>   
>>     
> Which PHY driver? The NPE code directly calls miiphy_read to acces 
> standard PHY registers, so where does a PHY driver come into play here?
>
>   
The way that you're doing it is correct - there is no PHY driver, only 
access methods. Hopefully this will change soon, but I'm unfortunately 
being distracted.
>> 	The best way is to add a function that request the phy status
>> 	and do not wait the phy autonegociation like done in the kernel
>> 	by read_status callback and it's implementation
>> 	genphy_read_status.
>>   
>>     
> I do not really see how that should work, for multiple reasons:
>  - speed/duplex on the MII bus depend on the attached switch and may be 
> different from the speed/duplex on any of the PHYs that are attached to 
> the switch.
>   
The only thing that matters is the speed/duplexity of the MII bus, which 
is fixed. When connected to a switch the link is always up, and the 
state of the network port needs to be determined by higher layers, most 
likely be a timeout.
>  - most switches (Marvell 88E6060 or similar) have multiple downstream 
> ports with PHYs - which one should I poll to get useful information? 
> Simply waiting for a link on any port will not guarantee that this is 
> the port via which the server is connected, so polling anything is 
> pretty useless IMHO.
>   

>  - there are switches (Marvell 88E6050) that have no MDIO interface - 
> they have a fixed MII speed/duplex, and the CPU has no way to know about 
> the status of any of the PHYs.
>
>   
There are others (Broadcom, anyway) that use SPI as control plane. The 
bottom line is that for fixed interfaces like this, software needs to 
hard-wire the link state, as you've done.
> I am a bit confused - could you please clarify in what direction the 
> code should evolve to solve these problems better than my patch does?
>
>   
Change the CONFIG_MII_ETHSWITCH to CONFIG_FIXED_PHY (as done in Linux) 
and I'll be happy. Later on we need to change things to have port-wise 
granularity, but we're not there yet.
> cu
> Michael
>
>   
regards,
Ben