Soekris 4826 USB failure on FreeBSD 7.0

[Hans Petter Selasky]

On Thursday 24 April 2008, John Baldwin wrote:
>
> This would indicate a bug in the bus_dmamap_load() call (wrong length?) and
> that is going to hose you when you do the bus_dmamap_sync() for systems
> with bounce pages (not enough data will get copied back and forth?).  You
> need to track down the real bug and fix it rather than adding a hack in
> your callback routine.

Hi John,

The minimum segment size is PAGE_SIZE bytes in my DMA-tag. Bus-dma starts 
counting at the memory location of the allocation. And not the memory 
location aligned to PAGE_SIZE bytes.

Memory pages:  |--------------|--------------|
My allocation: |---------XXXXXXXXXXXXX-------|

Sometimes when I allocate DMA memory I can end up having an allocation 
crossing two contiguous memory pages in physical memory. In those cases 
bus_dma does not give me the segment address of the second page in the 
segment list, because the allocation is less than PAGE_SIZE bytes. It fits 
within the values specified in the DMA tag. But in other cases, where the 
pages are not contiguous in RAM, bus_dma will return two different segment 
addresses.

The question is: Is this a bug or is it a feature?

--HPS