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

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Date:	Mon, 19 Aug 2013 15:31:13 +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 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.


>
> 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.

Regards,

Sonic

>
> let me know if it is ok
>
> I have just noticed that the no_csum_insertion could be removed and I'll
> provide a patch for it.
>
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