Subject: Re: bus_dma
To: Matt Thomas <>
From: Kamal R. Prasad <>
List: tech-kern
Date: 12/11/2004 21:41:31
--- Matt Thomas <> wrote:

> At 03:20 AM 12/11/2004, Kamal R. Prasad wrote:
> >Hello,
> >
> >  Can someone point me to src code that uses
> bus_dma to
> >share a block of memory between kernel and user
> space?
> uh, bus_dma isn't used for that.  

I looked at the paper by Jason Thorpe sometime back
and I BELIEVE it says it is used for kernel<-->user 
exchange of bulk data. Nevertheless, the suggestion to
use bus_dma is not mine.

> Could you explain
> what
> you are really trying to do?
I have written an mmap() interface for a usb device.
Userland does an mmap() to read in a block of data
without involving a copyout(). I am using vtophys()
[on freebsd for the moment] to map kernel virtual
address to a physical interface which is returned in
I have been given to understand that vtophys() will
not be available in future and I should use bus_dma in
future. The link below is the text of that email.

While my code is being developed on Freebsd, it will
be moved to arm-netbsd [after I get the hw in hand].

Thanks for any help.

> -- 
> Matt Thomas                     email:
> 3am Software Foundry              www:
> Cupertino, CA              disclaimer: I avow all
> knowledge of this message.

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