Subject: Re: [PATCH] ethernet: atheros: Add nss-gmac driver

From: [email-masked]
Date: Mon, 19 Jan 2015 21:58:09 -0000

> On Thursday 15 January 2015 08:12:51 [email-masked] wrote:
>>
>> The nss-gmac driver is for the internal GMAC IP in the Qualcomm IPQ806x
>> SoC. There are 2 ARM cores and 2 NSS cores inside the IPQ806x SoC. The
>> main purpose of these NSS cores is to offload the networking stack from
>> the ARM cores to achieve high performance at routing/ipsec..etc without
>> exhausting the ARM core CPU cycles. There is another nss-drv driver for
>> the NSS cores.
>
> I see.
>
>> The nss-gmac driver is designed to work standalone or with the nss-drv
>> driver so the switchable data plane overlay was implemented. When it
>> worked standalone, the data plane is running on the ARM core as a
>> standard
>> networking driver.
>
> How do you decide which way it gets used on a particular system?
>

By default the GMAC driver uses a native (Host ARM CPU) based data plane. 
If the configuration loads the offload nss-drv driver, the offload driver
registers an overlay with the GMAC.

>> The nss-drv driver can take over the data plane and
>> offload it to the NSS cores. The STMicro stmmac driver does not have
>> this
>> kind of overlay design so is not suitable for IPQ806x. This is why we
>> don't based on the stmmac driver
>
> Which kind of offload is implemented specifically? 'data plane' sounds
> fairly generic and could mean anything, and the code isn't readable enough
> in its current form for me to find out.

The Network Subsystem (NSS core) provides a GMAC pass-through until it is
given a rule to offload work.  Once a rule is given, it is capable of
performing: bridging, IPv4 NAT/FWD, IPv6 NAT/FWD, IPSec, LAG, and other
protocols.
> 	Arnd

Hope this clarify your question!

Thanks,
Stephen

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