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

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Message-ID: <5335DDC7.8040400@cogentembedded.com>
Date:	Fri, 28 Mar 2014 23:38:31 +0300
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Ben Dooks <ben.dooks@...ethink.co.uk>, netdev@...r.kernel.org
CC:	linux-sh@...r.kernel.org, magnus.damm@...nsource.se,
	nobuhiro.iwamatsu.yj@...esas.com
Subject: Re: [RFC] sh_eth: use RNC mode for R8A7790

Hello.

On 03/28/2014 07:46 PM, Ben Dooks 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.

WBR, Sergei

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