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Re: [PATCH V2 2/4] MIPS: Add board support for Loongson1B

To: Kelvin Cheung <keguang.zhang@gmail.com>
Subject: Re: [PATCH V2 2/4] MIPS: Add board support for Loongson1B
From: Giuseppe CAVALLARO <peppe.cavallaro@st.com>
Date: Mon, 24 Oct 2011 17:35:17 +0200
Cc: Wu Zhangjin <wuzhangjin@gmail.com>, linux-mips@linux-mips.org, linux-kernel@vger.kernel.org, ralf@linux-mips.org, r0bertz@gentoo.org, netdev@vger.kernel.org
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On 10/24/2011 4:05 PM, Kelvin Cheung wrote:
> 2011/10/24, Giuseppe CAVALLARO <peppe.cavallaro@st.com>:
>> Hello Kelvin.
>>
>> On 10/24/2011 12:36 PM, Kelvin Cheung wrote:
>>
>> [snip]
>>
>>> According to datasheet of Loongson 1B, the buffer size in RX/TX
>>> descriptor is only 2KB. So the Loongson1B's GMAC could not handle
>>> jumbo frames. And the second buffer is useless in this case. Am I
>>> right? Is there a better way than ifdef CONFIG_MACH_LOONGSON1 to
>>> avoid duplicate code?
>>
>> Sorry for my misunderstanding.
>>
>> I think you have to use the normal descriptor and remove the enh_desc
>> from the platform w/o modifying the driver at all.
>>
>> The driver will be able to select/configure all automatically (also jumbo).
>>
>> Let me know.
> 
> That's the problem.
> The bitfield definition of Loongson1B is also different from normal 
> descriptor.

The problem is not in the Loongson1B gmac.

The normal descriptor fields in the stmmac refer to an old synopsys
databook.
New chips have the same structure you have added; so we should fix this
in the driver w/o breaking the compatibility for old chips.
I kindly ask you to confirm if the currently normal descriptor structure
(w/o your changes) doesn't work on your platform.
Did you test it?

> Moreover, I want to enable the TX checksum offload function which is
> not supported in normal descriptor.
> Any suggestions?

It is supported but you have to pass from the platform: tx_coe = 1.

Peppe
> 
>> Note:
>> IIRC, there is a bit difference in case of normal descriptors for
>> Synopsys databook newer than the 1.91 (I used for testing this mode).
>> In any case, I remember that, on some platforms, the normal descriptors
>> have been used w/o problems also on these new chip generations.
>>
>> Peppe
>>
>>
> 
> 


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