Re: [RFC] sh_eth: use RNC mode for R8A7790

[Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>]

Hello.

On 04/14/2014 08:48 PM, Geert Uytterhoeven wrote:

>>>>> The current behaviour of the sh_eth driver is not to use the RNC bit
>>>>> for the receive ring. This means that every packet recieved is not only
>>>>> generating an IRQ but it also stops the receive ring DMA as well until
>>>>> the driver re-enables it after unloading the packet.

>>>>> This means that a number of the following errors are generated due to
>>>>> the receive packet FIFO overflowing due to nowhere to put packets:

>>>>>      net eth0: Receive FIFO Overflow

>>>>> Setting the RMCR_RNC configuration has so far been tested with an NFS
>>>>> root filesystem and the driver has not failed yet. It is not yet known
>>>>> why this is not set for R8A779x operation

>>>>      The reason is simple: it's not set on almost all 100 Mbs devices
>>>> except SH7757 (and most recently added R7S72100), so this was a matter
>>>> of copy-paste. I've had setting this bit on at least R-Car devices on my
>>>> aganda for some time but couldn't get to it yet.

>>>>> (Feedback on this issue or other testing is welcome)

>>>>      OK, I'll try it with netperf UDP test known to generate handful of
>>>> the aforementioned errors, when I have time.

>>> Has anyone had time to look at this?

>> I gave it a try on Koelsch (it does apply to r8a7791, too, right?), and didn't
>> see any good or ill effects. Just using NFS root and generating some I/O,
>> so nothing fancy.

> FWIW, I still have "renesas,no-ether-link" in the ethernet node in DT.

    You shouldn't need it anymore if you're using recent devel branch of the 
renesas.git repo: it already has the necessary PHY driver and device tree 
changes to avoid the issue which specifying that prop fixed.

> Gr{oetje,eeting}s,

WBR, Sergei