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From: Hans Petter Selasky <hselasky@c2i.net>
To: freebsd-usb@freebsd.org
Date: Sat, 8 Nov 2008 13:53:09 +0100
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Cc: freebsd-current@freebsd.org
Subject: Re: (FWD) Serious busdma bug in -current in relation to USB harware.
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On Saturday 08 November 2008, Alexander Motin wrote:
> Hans Petter Selasky wrote:
> > http://perforce.freebsd.org/chv.cgi?CH=152649
> >
> > Change 152649 by hselasky@hselasky_laptop001 on 2008/11/08 09:09:50
> >
> >
> >     Fix a serious BUSDMA bug: The initial virtual page offset is
> >     not retained on the bounce pages, which is what the EHCI and
> >     the OHCI expects.
>
> I'm sorry, but are you sure with this? If bounce page will have the same
> page offset as original data, then how bus_dma_tag_create()'s alignment
> parameter expected to work? What if data are misaligned, but hardware
> require alignment?

Hi,

I'm not saying that my patch is fully correct for all cases, but at least it 
solves the USB case. USB uses an alignment of 1-byte for data.

Probably someone needs to sit down a think this through. Like it is now, it is 
very scary with regard to USB!

Maybe it is time to create a new busdma tag flag? BUS_DMA_NOREALIGN?

If this flag is set, busdma should refuse to load the memory if the memory is 
not aligned already to the given aligment in the DMA tag ?

--HPS