From: Stephen Hemminger <shemminger@osdl•org>
To: "Amit S. Kale" <amitkale@netxen•com>
Cc: netdev@vger•kernel.org, brazilnut@us•ibm.com, jeff@garzik•org,
wendyx@us•ibm.com, sanjeev@netxen•com, rob@netxen•com,
netxenproj@linsyssoft•com
Subject: Re: [PATCH 3/3] NetXen: 64-bit memory fixes, driver cleanup
Date: Tue, 28 Nov 2006 10:40:32 -0800 [thread overview]
Message-ID: <20061128104032.6d3121ac@freekitty> (raw)
In-Reply-To: <Pine.LNX.4.64.0611280733110.6776@dut39>
On Tue, 28 Nov 2006 08:04:40 -0800 (PST)
"Amit S. Kale" <amitkale@netxen•com> wrote:
> Hi Stephen,
>
> <SNIP>
> > > > you need explicit bounce buffers. If you can't DMA from unaligned
> address,
> > > > > the write a small routine to copy the skb to a new one.
> > > >
> > > >
> > > > The hardware supports DMA into 35 bit addresses. The intent is to
> > > > enable DMA into addresses upto 32G.
> > > >
> > >
> > > You should then set the same value for pci_set_dma_mask, because then
> the IOMMU
> > > can help. See both b44 or tg3 drivers, they have to deal with odd size
> masks.
> > > I don't think you have to do all the bounce buffer work in the driver.
>
> Using bounce buffers has following tradeoffs:
> 1. Overhead of code maintenance.
> 2. Slow performance.
> Also on some ia64 machines we saw reduced performance because of larger
> ring sizes.
>
> But if we remove bounce buffers and use IOMMU instead, it might not
> work for some Opteron configurations. On one of our Opterons we could not
> set the IOMMU from kernel command line (it asked to set it from the BIOS where there was no
> such option in the BIOS)
>
> So what do you suggest, should we use the IOMMU or should we keep the
> bounce buffers as they are?
>
> Thanks,
> Amit Kale.
I don't mind workarounds, it is just that the problem is not unique to your driver
and we need a platform or general solution. There are lots of devices that stupid
hardware and need smaller masks.
--
Stephen Hemminger <shemminger@osdl•org>
next prev parent reply other threads:[~2006-11-28 19:05 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-11-28 16:04 Re: [PATCH 3/3] NetXen: 64-bit memory fixes, driver cleanup Amit S. Kale
2006-11-28 18:40 ` Stephen Hemminger [this message]
-- strict thread matches above, loose matches on Subject: below --
2006-11-17 15:36 Linsys Contractor Amit S. Kale
2006-11-17 16:40 ` Stephen Hemminger
2006-11-18 10:28 ` Sanjeev Jorapur
2006-11-20 18:45 ` Stephen Hemminger
2006-11-23 16:32 ` Sanjeev Jorapur
2006-11-27 18:23 ` Stephen Hemminger
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