netdev - RE: [PATCH net-next 0/6] net: stmmac: Improvements for -next

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Date:   Wed, 11 Sep 2019 08:59:45 +0000
From:   Jose Abreu <Jose.Abreu@...opsys.com>
To:     David Miller <davem@...emloft.net>,
        "Jose.Abreu@...opsys.com" <Jose.Abreu@...opsys.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "Joao.Pinto@...opsys.com" <Joao.Pinto@...opsys.com>,
        "peppe.cavallaro@...com" <peppe.cavallaro@...com>,
        "alexandre.torgue@...com" <alexandre.torgue@...com>,
        "mcoquelin.stm32@...il.com" <mcoquelin.stm32@...il.com>,
        "linux-stm32@...md-mailman.stormreply.com" 
        <linux-stm32@...md-mailman.stormreply.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH net-next 0/6] net: stmmac: Improvements for -next

From: David Miller <davem@...emloft.net>
Date: Sep/11/2019, 09:21:55 (UTC+00:00)

> From: Jose Abreu <Jose.Abreu@...opsys.com>
> Date: Tue, 10 Sep 2019 16:41:21 +0200
> 
> > Misc patches for -next. It includes:
> >  - Two fixes for features in -next only
> >  - New features support for GMAC cores (which includes GMAC4 and GMAC5)
> 
> Series applied, but what exactly does "ARP offload" even do?

ARP Offload allows the IP to reply to ARP_REQUEST packets automatically 
without passing by the application.

As net doesn't support this offloading I'm currently using this feature 
to test endianness issues in the IP and check if MAC Address is 
correctly configured, the logic is as follows:
 - MAC is set in loopback mode and ARP offload is activated
 - selftests create a dummy ARP_REQUEST packet and send it out
 - IP will detect the ARP_REQUEST packet and generate an ARP_REPLY 
packet
 - As MAC is in loopback mode then selftests will receive the ARP_REPLY 
packet
 - selftests logic will check if ARP_REPLY packet is correct (i.e. MAC 
address and packet type)

This way if this test fails it probably indicates that MAC address of IP 
is not correctly configured or that endianness of the IP was changed 
from default setting (which is LE).

By default the feature is off because user may not want to reply to 
ARP_REQUEST and I'm more using it as a diagnose facility. Let me know if 
you agree with this approach.

---
Thanks,
Jose Miguel Abreu