linux-kernel - Re: Driver: PCIe: 'pci_map_sg' returning invalid bus address?

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Date:	Sun, 15 Aug 2010 21:31:29 -0600
From:	Robert Hancock <hancockrwd@...il.com>
To:	Evan Lavelle <sa212+lkml@...onix.com>
CC:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Driver: PCIe: 'pci_map_sg' returning invalid bus address?

On 08/14/2010 09:25 AM, Evan Lavelle wrote:
> Thanks guys. I had to get this working quickly so I just stuck with my
> bounce buffer code. I'm not sure that it's technically a 'bounce
> buffer'; it just so happens that 'pci_alloc_consistent' returns an
> address in the low 32 bits. This may stop working if the user installs
> more than 4Gig of memory but I can live with that for now. Performance

That should be safe as far as x86-32 goes - pci_alloc_consistent will 
return a low memory address which will be below 1GB.

> isn't great (~110Mbytes/s on 4-channel PCIe) but it's good enough.
>
> It's disappointing that LDD didn't have anything to say about this; it's
> pretty fundamental to DMA on x86_32 and PAE.

The situation kind of sucks with that combination, yes. The block and 
network subsystems have their own workarounds but other drivers just 
have to sort of hack something together.
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