netdev - Re: ixp4xx eth broken in 3.7.0/3.8-rc5?

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Message-ID: <20744.61933.566806.942439@pilspetsen.it.uu.se>
Date:	Wed, 30 Jan 2013 11:11:57 +0100
From:	Mikael Pettersson <mikpe@...uu.se>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	Xi Wang <xi.wang@...il.com>, Mikael Pettersson <mikpe@...uu.se>,
	<linux-arm-kernel@...ts.infradead.org>,
	Imre Kaloz <kaloz@...nwrt.org>,
	Krzysztof Halasa <khc@...waw.pl>, <netdev@...r.kernel.org>
Subject: Re: ixp4xx eth broken in 3.7.0/3.8-rc5?

Ben Hutchings writes:
 > On Tue, 2013-01-29 at 19:32 -0500, Xi Wang wrote:
 > > On 1/29/13 7:11 PM, Mikael Pettersson wrote:
 > > > A git bisect identified the following as the culprit:
 > > > 
 > > >   > From 1a4901177574083c35fafc24c4d151c2a7c7647c Mon Sep 17 00:00:00 2001
 > > >   > From: Xi Wang <xi.wang@...il.com>
 > > >   > Date: Sat, 17 Nov 2012 20:25:09 +0000
 > > >   > Subject: [PATCH] ixp4xx_eth: avoid calling dma_pool_create() with NULL dev
 > > >   >
 > > >   > Use &port->netdev->dev instead of NULL since dma_pool_create() doesn't
 > > >   > allow NULL dev.
 > > >   >
 > > >   > Signed-off-by: Xi Wang <xi.wang@...il.com>
 > > >   > Cc: Andrew Morton <akpm@...ux-foundation.org>
 > > >   > Signed-off-by: David S. Miller <davem@...emloft.net>
 > > >   > ---
 > > >   >  drivers/net/ethernet/xscale/ixp4xx_eth.c |    8 +++++---
 > > >   >  1 files changed, 5 insertions(+), 3 deletions(-)
 > > > 
 > > > Reverting this unbreaks ixp4xx_eth on my ixp4xx machine with kernels
 > > > 3.7.0 and 3.8-rc5.
 > > 
 > > Thanks.  The problem was that in init_queues(), the dma_pool_create()
 > > call requires a non-null dev.
 > > 
 > >   dma_pool = dma_pool_create(DRV_NAME, ??, ...);

I had a look around in the 3.8-rc5 kernel source.

mm/dmapool.c:dma_pool_create() needs a non-NULL dev in the CONFIG_NUMA case,
because it calls dev_to_node(dev) which dereferences dev if CONFIG_NUMA.
But in the non-CONFIG_NUMA case there is no dereference of dev, and in fact
there is an explicit check for dev being NULL or not towards the end of
dma_pool_create().  So that explains why ixp4xx works without the change:
it's not NUMA.

A quick grep found three calls to dma_pool_create() with a NULL dev parameter,
two in drivers/usb/gadget/amd5536udc.c and one in arch/arm/mach-s3c64xx/dma.c.
These would all be broken with CONFIG_NUMA but Ok otherwise.

 > > 
 > > What do you think would work here?
 > 
 > For DMA purposes I would expect the right device to be the parent bus
 > device, i.e. port->netdev->dev.parent.  The driver might also need to
 > set its DMA masks.

At least on ixp4xx the DMA masks are normally set by the platform PCI init
code (it has a 64MB PCI DMA window limitation).

I can give the port->netdev->dev.parent variant a try later this evening.

/Mikael
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