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Subject: Re: [PATCH net 2/4] net: ravb: Allow RX loop to move past DMA mapping
 errors
To: Paul Barker <paul.barker.ct@bp.renesas.com>, "David S. Miller"
	<davem@davemloft.net>, Eric Dumazet <edumazet@google.com>, Jakub Kicinski
	<kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
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	Geert Uytterhoeven <geert+renesas@glider.be>
CC: <netdev@vger.kernel.org>, <linux-renesas-soc@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>
References: <20240411114434.26186-1-paul.barker.ct@bp.renesas.com>
 <20240411114434.26186-3-paul.barker.ct@bp.renesas.com>
From: Sergey Shtylyov <s.shtylyov@omp.ru>
Organization: Open Mobile Platform
Message-ID: <e7fea01d-d549-cd8c-8d7f-ed403ca980fa@omp.ru>
Date: Thu, 11 Apr 2024 19:37:50 +0300
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On 4/11/24 2:44 PM, Paul Barker wrote:

> The RX loops in ravb_rx_gbeth() and ravb_rx_rcar() skip to the next loop
> interation if a zero-length descriptor is seen (indicating a DMA mapping

   Iteration. :-)

> error). However, the current rx descriptor index `priv->cur_rx[q]` was

   RX?

> incremented at the end of the loop and so would not be incremented when
> we skip to the next loop iteration. This would cause the loop to keep
> seeing the same zero-length descriptor instead of moving on to the next
> descriptor.
> 
> As the loop counter `i` still increments, the loop would eventually
> terminate so there is no risk of being stuck here forever - but we
> should still fix this to avoid wasting cycles.
> 
> To fix this, the rx descriptor index is incremented at the top of the

   RX?

> loop, in the for statement itself. The assignments of `entry` and `desc`
> are brought into the loop to avoid the need for duplication.
> 
> Fixes: d8b48911fd24 ("ravb: fix ring memory allocation")
> Signed-off-by: Paul Barker <paul.barker.ct@bp.renesas.com>

Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>

[...]

MBR, Sergey