netdev - Re: [RFC PATCH v2 0/2] nb8800 suspend/resume support

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Date:   Wed, 2 Aug 2017 17:52:59 +0200
From:   Mason <slash.tmp@...e.fr>
To:     Mans Rullgard <mans@...sr.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC PATCH v2 0/2] nb8800 suspend/resume support

On 02/08/2017 17:36, Måns Rullgård wrote:

> Mason wrote:
> 
>> Looking at the tango-specific integration, I note this nugget:
>>
>> 1.5.4 Stopping & Starting the DMA
>>
>> This feature has been added to allow the software to stop and start
>> the DMA without any issues.
>>
>> Procedure:
>> 1- STOP:
>> 2- Stop RX core;
>> 3- Set OWN bit of all descriptor of the chain to 1;
>> 4- Stop DMA by writing dma_stop bit to 1 in  RX_DMA_Stop register
>> 5- Wait around 100 clock cycles.
>>
>> The pending packets are held until the system will re-start.
>>
>> RE-START:
>> 1- Clear dma_stop bit (note that if at the time of stopping the DMA,
>> the next packet in the FIFO was an UDP packet, when clearing dma_stop,
>> this packet will directly start being written in the DRAM since UDP
>> packets are not controlled by the descriptor mechanism);
>> 2- Program a new chain of descriptor;
>> 3- Re-enable DMA (rx_ctrl register)
>>
>> rx_dma_stop:
>> Software control to stop the Rx DMA.
>> A write to this bit with "1" will gracefully stop the Rx DMA by after
>> transferring the current packet. If more packets are pending they will
>> be held until the software clears this bit.
>>
>> Hmmm, what do you think? This looks promising...
> 
> This is only available in the more recent Sigma versions.  Although it
> is nicer, I didn't think it was worth the trouble to support both
> methods since the older method should work on all chips.

Well, from my perspective, the older method does not
work on newer chips :-)

The "new" method is available on the SMP8670 onward
(released Jan 2011). I might try implementing it for
"sigma,smp8734-ethernet" boards.

Regards.