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

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Date:	Mon, 14 Apr 2014 18:35:21 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Ben Dooks <ben.dooks@...ethink.co.uk>
Cc:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Linux-sh list <linux-sh@...r.kernel.org>,
	magnus.damm@...nsource.se,
	Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@...esas.com>
Subject: Re: [RFC] sh_eth: use RNC mode for R8A7790

Hi Ben,

On Mon, Apr 14, 2014 at 2:47 PM, Ben Dooks <ben.dooks@...ethink.co.uk> wrote:
> On 28/03/14 20:38, Sergei Shtylyov wrote:
>> 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.
>
> 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.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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