Subject: Re: DMA buffers
To: Marcus Comstedt <>
From: Jason R Thorpe <>
List: port-dreamcast
Date: 01/19/2001 10:32:59
On Wed, Jan 10, 2001 at 01:06:52AM +0100, Marcus Comstedt wrote:

 > For the Maple Bus driver, I need to allocate some contiguous physical
 > memory for use as DMA buffers.  The code I use currently looks in
 > principle like this:
 >  paddr_t dmabuf = SH3_P2SEG_TO_PHYS(vtophys(uvm_km_alloc(phys_map, SIZE)))
 > Can someone confirm that this is the right way to do it?  I'm a little
 > confused that the vtophys function returns a P2 address rather than a
 > physical address...

Not even that is completely safe.

The Right Thing To Do would be to implement the framework described in
bus_dma(9).  This is particularly important for when you get the broadband
adapter working, which as I understand it, is a SHB->PCI bridge with a
PCI Ethernet chip on the other side.

        -- Jason R. Thorpe <>