netdev - Re: Bug: mv643xxx fails with highmem

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Message-ID: <5489FDB4.5060701@free-electrons.com>
Date:	Thu, 11 Dec 2014 17:25:24 -0300
From:	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>,
	David Miller <davem@...emloft.net>,
	Nimrod Andy <B38611@...escale.com>,
	Fabio Estevam <fabio.estevam@...escale.com>
CC:	netdev@...r.kernel.org,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Gregory CLEMENT <gregory.clement@...e-electrons.com>
Subject: Re: Bug: mv643xxx fails with highmem

On 12/11/2014 05:25 PM, Russell King - ARM Linux wrote:
> On Thu, Dec 11, 2014 at 03:10:55PM -0500, David Miller wrote:
>> From: Russell King - ARM Linux <linux@....linux.org.uk>
>> Date: Thu, 11 Dec 2014 19:49:20 +0000
>>
>>> Commit 69ad0dd7af22 removed skb_frag_dma_map() in favour of mapping
>>> all fragments with dma_map_single().  This fails when the driver is
>>> used in an environment with highmem.
>>
>> This change looks really buggy to me.
>>
>> Unfortunately, all the changes he subsequently makes for software TSO
>> support depend upon this :-/
>>
>> The change is definitely wrong.
> 
> Thanks for confirming where the bug is.
> 
> Would other drivers need fixing for this as well?  Eg, fec_main.c
> does the following, and this driver is used on iMX6 which can also have
> highmem:
> 
> static int
> fec_enet_txq_submit_frag_skb(struct fec_enet_priv_tx_q *txq,
>                              struct sk_buff *skb,
>                              struct net_device *ndev)
> {
>                 bufaddr = page_address(this_frag->page.p) + this_frag->page_offset;
> ...
>                 addr = dma_map_single(&fep->pdev->dev, bufaddr, frag_len,
>                                       DMA_TO_DEVICE);
> 

And mvneta seems to have that pattern too: see mvneta_tx_frag_process().
-- 
Ezequiel García, Free Electrons
Embedded Linux, Kernel and Android Engineering
http://free-electrons.com
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