Re: DMA memory mapping

[Christine Ames <clgisotti@yahoo.com>]

--- David Stroupe <dstroupe@keyed-upsoftware.com> wrote:
> I am developing a framegrabber driver.  I need to map memory for
> the 
> grabber to DMA the images into.  I have it working currently where
> the 
> grab happens into kernel memory and then I copy_to_user to get the 
> buffer into user space.  I think I can eliminate this step by using
> 
> remap_page_range which would allow me to access the grabbed images 
> directly from user space.  The argument to remap_page_range that I
> don't 
> understand is the first argument...the virtual address.  I know how
> big 
> the buffer is, I know the physical address of the buffer allocated
> in 
> the kernel, I have to set the protection such that the pages are
> not 
> swapped...how do I get a virtual address to pass to the driver so
> that 
> this mapping can take place?
> 

__va() will work, but only with low memory addresses.

See http://www.xml.com/ldd/chapter/book/ch13.html#t1

Best of luck, ;-)

--Christine


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