netdev - Re: [PATCH net] gianfar: Fix dma check map error when DMA_API

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Date:	Wed, 10 Dec 2014 13:13:47 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	claudiu.manoil@...escale.com
Cc:	netdev@...r.kernel.org, haokexin@...il.com
Subject: Re: [PATCH net] gianfar: Fix dma check map error when
 DMA_API_DEBUG is enabled

From: Claudiu Manoil <claudiu.manoil@...escale.com>
Date: Tue, 9 Dec 2014 16:24:35 +0200

> From: Kevin Hao <haokexin@...il.com>
> 
> We need to use dma_mapping_error() to check the dma address returned
> by dma_map_single/page(). Otherwise we would get warning like this:
 ...
> For TX, we need to unmap the pages which has already been mapped and
> free the skb before return. For RX, just let the rxbdp as unempty.
> We can retry to initialize it to empty in next round.
> 
> Signed-off-by: Kevin Hao <haokexin@...il.com>
> Signed-off-by: Claudiu Manoil <claudiu.manoil@...escale.com>

The RX behavior needs to be adjusted.

You should never leave holes in the RX ring, ever.

Instead, try allocating the new RX skb first, and only if
you are successful should you pass up the original SKB.  If
it fails, then reuse the original SKB in the RX ring.
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