netdev - Re: [PATCH] driver:net:stmmac: Disable DMA store and forward mode if platform data force_sf_dma

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Message-ID: <CAJxxZ0NFhMMKp2eB+b168=c6+JsmJE6-yva7ZOGKciK3e4b8Yg@mail.gmail.com>
Date:	Mon, 19 Aug 2013 18:51:03 +0800
From:	Sonic Zhang <sonic.adi@...il.com>
To:	Giuseppe CAVALLARO <peppe.cavallaro@...com>
Cc:	netdev <netdev@...r.kernel.org>,
	adi-buildroot-devel@...ts.sourceforge.net,
	Sonic Zhang <sonic.zhang@...log.com>
Subject: Re: [PATCH] driver:net:stmmac: Disable DMA store and forward mode if
 platform data force_sf_dma_mode is negative.

Hi Giuseppe,

On Mon, Aug 19, 2013 at 3:45 PM, Giuseppe CAVALLARO
<peppe.cavallaro@...com> wrote:
> On 8/19/2013 9:31 AM, Sonic Zhang wrote:
>>
>> Hi Giuseppe,
>>
>> On Mon, Aug 19, 2013 at 2:03 PM, Giuseppe CAVALLARO
>> <peppe.cavallaro@...com> wrote:
>>>
>>> Hello Sonic
>>>
>>>
>>> On 8/15/2013 9:37 AM, Sonic Zhang wrote:
>>>>
>>>>
>>>> From: Sonic Zhang <sonic.zhang@...log.com>
>>>>
>>>> Some synopsys ip implementation doesn't support DMA store and forward
>>>> mode,
>>>> such as BF60x. So, define force_sf_dma_mode negative to use DMA
>>>> thresholds
>>>> only.
>>>
>>>
>>>
>>> I think that you should not pass the force_sf_dma_mode platform field
>>> at all (and it doesn't make sense to force it as negative).
>>> To use the threshold you should reset tx_coe. In fact, your HW cannot
>>> perform the Hw csum if SF is not available.
>>> Note that, the HW cap register (if available) can override (set/reset)
>>>   tx_coe.
>>
>>
>> Even if I reset tx_coe, the SF mode is still set to RX DMA in current
>> stmmac_dma_operation_mode(). SF mode is not supported in both RX DMA
>> and TX DMA in Blackfin MAC.
>
>
> yes this is true. the SF is always set for the RX path because I have
> never had and known HW w/o RX csum (since the 209).
>
> So I think the code could be improved to disable/enable the SF also for
> the RX path.
>
>
>>>
>>> I tested, long time ago, this scenario on old mac w/o HW cap register
>>> and w/o SF.
>>
>>
>> Blackfin synopsys MAC IP has the HW cap register with tx_coe set to 1,
>> but the HW tx_coe doesn't really work. I have the other patch to
>> disable HW tx_coe in board file and override the HW cap register.
>
>
> AFAIK the HW shouldn't be able to perform the csum in HW w/o SF.
>
> Maybe, an easy way could be to use a new field to force the threshold
> mode. This should also remove the csum in HW (IMO) and program the
> DMA operation register.
>

The problem is that HW RX csum works perfectly on Blackfin MAC
although the SF mode is not supported in RX DMA. I may need 2 platform
fields to force RX DMA threshold and disable HW tx_coe. One field
doesn't cover both cases well.

Which 2 fields do you prefer?

Thanks

Sonic
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