netdev - Re: [PATCH v2] sh_eth: use RNC mode for R8A7790/R87791

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Date:	Wed, 04 Jun 2014 00:02:19 +0400
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Ben Dooks <ben.dooks@...ethink.co.uk>,
	David Miller <davem@...emloft.net>
CC:	linux-kernel@...ethink.co.uk, netdev@...r.kernel.org,
	nobuhiro.iwamatsu.yj@...esas.com, magnus.damn@...nsource.se,
	horms@...ge.net.au, yoshihiro.shimoda.uh@...esas.com,
	cm-hiep@...so.co.jp, linux-sh@...r.kernel.org
Subject: Re: [PATCH v2] sh_eth: use RNC mode for R8A7790/R87791

Hello.

On 06/03/2014 03:19 PM, Ben Dooks wrote:

>>>>>>>       Looks like the early SH2/3 SoCs didn't implement the whole
>>>>>>> register.
>>>>>>> Despite that, sh_eth_dev_init() always writes to this register... :-/
>>>>>>> So far, the RMCR.RNC bit was mostly set for the Gigabit-capable
>>>>>>> controllers, however that rule wasn't strictly followed. Well, this
>>>>>>> driver is still a mess, and it's hard to deal with it without the
>>>>>>> necessary documentation.

>>>>>> Why don't we therefore:

>>>>>> 1) Skip the register write if the per-chip value is zero.

>>>>>      I rather thought about not writing when the register is not
>>>>>      implemented.
>>>>> I'll probably look into this when I have time.

>>>>>> 2) Add the RNC bit to all of the gigabit capable controllers.

>>>>>      I probably misspoke -- all the Gigabit controllers already have it
>>>>> set, it's just that some 100 MBbps ones have it set, but most
>>>>> don't.

>>>> So these chips that do not implement the register, they only process
>>>> one RX descriptor at a time until the interrupt handler re-enables
>>>> DMA receive?

>>>      I just don't know. Looks like the driver is broken on SH2/3 even
>>> more than
>>> I thought: it always reads the EDRRR register in sh_eth_rx() trying to
>>> understand if the reception has been stopped but that register doesn't
>>> seem to
>>> exist on SH2/3. Moreover, sh_eth_interrupt() reads EESR in order to
>>> determine
>>> the interrupt status but that register doesn't seem to exist on SH2/3
>>> either!

>>     OK, I've chased down the commit that broke SH2/3 support 3+ years
>> ago; here it is:

>> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=4a55530f38e4eeee3afb06093e81309138fe8360

>>     All the registers I've mentioned did exist on SH2/3, they just got
>> missed in the mapping arrays.

> I suppose it would be a good idea to submit a patch to add these then.

    Not that I'm supposed to fix the old SH machines now but I've just posted 
the patch. :-)

WBR, Sergei

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