linux-kernel - Re: [linux-dvb] Re: [PATCH] Re: More than 2Gb problem (dvb related) ?

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Date:	Mon, 30 Apr 2007 02:22:36 +0200
From:	Oliver Endriss <o.endriss@....de>
To:	linux-dvb@...uxtv.org
Cc:	Jon Burgess <jburgess777@...glemail.com>,
	linux-kernel@...r.kernel.org, v4l-dvb-maintainer@...uxtv.org,
	Lee Revell <rlrevell@...-job.com>,
	Gregoire Favre <Gregoire.Favre@...il.com>
Subject: Re: [linux-dvb] Re: [PATCH] Re: More than 2Gb problem (dvb related) ?

Jon Burgess wrote:
> On Sat, 2007-04-28 at 18:17 +0100, Jon Burgess wrote:
> > On Fri, 2007-04-27 at 18:06 -0400, Lee Revell wrote:
> > > On 4/27/07, Jon Burgess <jburgess777@...glemail.com> wrote:
> > > > Interesting - I see similar symptoms after upgrading my PC:
> > > > * old PC was AMD Athlon 64 3000 w/ 2GB of RAM which had no issues
> > > > * new PC is a Intel Core 2 Duo w/ 4GB of RAM and fails in the way you
> > > > describe.
> > > 
> > > Driver using an incorrect DMA mask?
> > > 
> > > Lee
> > 
> > It appears the problem is that the driver is using streamed PCI and
> > needs to explicitly sync the data otherwise it breaks when the SWIOTLB
> > is in use. A call to pci_unmap_sg() was missing too.
> > 
> > This patch is against the current v4l-dvb HG tree.
> > 
> > I've only tested the change with a budget-ci card.
> > 
> > 	Jon
> > 
> > Signed-off-by: Jon Burgess <jburgess777@...glemail.com>
> 
> While the above patch works, it seems the underlying causes is that
> vmalloc_32() is providing memory above 4Gb on x86-64 which is not what
> the driver expects. This same issue came up a few weeks ago with regards
> to DRM on radeon http://lkml.org/lkml/2007/4/1/257
> 
> Andi Kleen included a patch to ensure vmalloc_32() returns memory <4Gb
> in a patch which is currently in -mm
>  http://kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.21-rc7/2.6.21-rc7-mm2/broken-out/x86_64-mm-vmalloc-32.patch
> 
> With this patch applied the current driver appears to work OK. 
> 
> Attached is a smaller patch against v4l-dvb which just adds the missing
> pci_unmap_sg() call.

Imo your patch is correct and should be applied.
Any objections?

After digging through the code, kernel DMA docs and the saa7146
datasheet, I think that we should remove the scatter-gatter voodoo
from the budget and av7110 driver. ;-)

What about the attached patch?
- easy to understand and maintain
- saves 1 page of memory (page table of the SAA7146 MMU)
- saves PCI bandwidth (SAA7146 does not read page table anymore)

Comments?

CU
Oliver

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