netdev - Re: [PATCH net-next] Revert "dpaa2-eth: configure the cache stashing amount on a queue"

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Message-Id: <20190523.093732.2092755980021095694.davem@davemloft.net>
Date:   Thu, 23 May 2019 09:37:32 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     ruxandra.radulescu@....com
Cc:     netdev@...r.kernel.org, ioana.ciornei@....com
Subject: Re: [PATCH net-next] Revert "dpaa2-eth: configure the cache
 stashing amount on a queue"

From: Ioana Radulescu <ruxandra.radulescu@....com>
Date: Thu, 23 May 2019 17:38:22 +0300

> This reverts commit f8b995853444aba9c16c1ccdccdd397527fde96d.
> 
> The reverted change instructed the QMan hardware block to fetch
> RX frame annotation and beginning of frame data to cache before
> the core would read them.
> 
> It turns out that in rare cases, it's possible that a QMan
> stashing transaction is delayed long enough such that, by the time
> it gets executed, the frame in question had already been dequeued
> by the core and software processing began on it. If the core
> manages to unmap the frame buffer _before_ the stashing transaction
> is executed, an SMMU exception will be raised.
> 
> Unfortunately there is no easy way to work around this while keeping
> the performance advantages brought by QMan stashing, so disable
> it altogether.
> 
> Signed-off-by: Ioana Radulescu <ruxandra.radulescu@....com>

Applied.