netdev - Re: Bug: mv643xxx fails with highmem

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Message-ID: <20141211202507.GS11285@n2100.arm.linux.org.uk>
Date:	Thu, 11 Dec 2014 20:25:07 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	David Miller <davem@...emloft.net>,
	Nimrod Andy <B38611@...escale.com>,
	Fabio Estevam <fabio.estevam@...escale.com>
Cc:	ezequiel.garcia@...e-electrons.com, netdev@...r.kernel.org
Subject: Re: Bug: mv643xxx fails with highmem

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);

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