netdev - Re: [PATCH] 8139cp: set ring address after enabling C+ mode

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Message-Id: <20121125.155457.1039099162410338935.davem@davemloft.net>
Date:	Sun, 25 Nov 2012 15:54:57 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	dwmw2@...radead.org
Cc:	jgarzik@...ox.com, jasowang@...hat.com, netdev@...r.kernel.org
Subject: Re: [PATCH] 8139cp: set ring address after enabling C+ mode

From: David Woodhouse <dwmw2@...radead.org>
Date: Wed, 21 Nov 2012 20:27:19 +0000

> This fixes (for me) a regression introduced by commit b01af457 ("8139cp:
> set ring address before enabling receiver"). That commit configured the
> descriptor ring addresses earlier in the initialisation sequence, in
> order to avoid the possibility of triggering stray DMA before the
> correct address had been set up.
> 
> Unfortunately, it seems that the hardware will scribble garbage into the
> TxRingAddr registers when we enable "plus mode" Tx in the CpCmd
> register. Observed on a Traverse Geos router board.
> 
> To deal with this, while not reintroducing the problem which led to the
> original commit, we augment cp_start_hw() to write to the CpCmd register
> *first*, then set the descriptor ring addresses, and then finally to
> enable Rx and Tx in the original 8139 Cmd register. The datasheet
> actually indicates that we should enable Tx/Rx in the Cmd register
> *before* configuring the descriptor addresses, but that would appear to
> re-introduce the problem that the offending commit b01af457 was trying
> to solve. And this variant appears to work fine on real hardware.
> 
> Signed-off-by: David Woodhouse <David.Woodhouse@...el.com>

Applied to net-next.
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