linux-kernel - Re: Regarding tx-nocache-copy in the Sheevaplug

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Message-ID: <20141015215701.GA4109@f1.synalogic.ca>
Date:	Wed, 15 Oct 2014 14:57:01 -0700
From:	Benjamin Poirier <benjamin.poirier@...il.com>
To:	Lluís Batlle i Rossell <viric@...ic.name>
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	Carles Pagès <page@...ata.homelinux.net>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: Regarding tx-nocache-copy in the Sheevaplug

On 2014/10/13 12:52, Lluís Batlle i Rossell wrote:
> Hello,
> 
> on the 7th of January 2014 ths patch was applied:
> https://lkml.org/lkml/2014/1/7/307
> 
> [PATCH v2] net: Do not enable tx-nocache-copy by default
>         
> In the Sheevaplug (ARM Feroceon 88FR131 from Marvell) this made packets to be
> sent corrupted. I think this machine has something special about the cache.
> 
> Enabling back this tx-nocache-copy (as it used to be before the patch) the
> transfers work fine again. I think that most people, encountering this problem,
> completely disable the tx offload instead of enabling back this setting.
> 
> Is this an ARM kernel problem regarding this platform?

This is odd, only x86 defines ARCH_HAS_NOCACHE_UACCESS. On arm,
skb_do_copy_data_nocache() should end up using __copy_from_user()
regardless of tx-nocache-copy.
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