Re: [alsa-devel] USB transfer_buffer allocations on 64bit systems

[FUJITA Tomonori]

On Fri, 7 May 2010 10:51:10 -0400 (EDT)
Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:

> On Fri, 7 May 2010, Daniel Mack wrote:
> 
> > > At least the audio class and ua101 drivers don't do this and fill the
> > > buffers before they are submitted.
> > 
> > Gnaa, you're right. I _thought_ my code does it the way I described, but
> > what I wrote is how I _wanted_ to do it, not how it's currently done. I
> > have a plan to change this in the future.
> > 
> > So unfortunately, that doesn't explain it either. Sorry for the noise.
> 
> At one point we tried an experiment, printing out the buffer and DMA 
> addresses.  I don't recall seeing anything obviously wrong, but if an 
> IOMMU was in use then that might not mean anything.  Is it possible 
> that the IOMMU mappings sometimes get messed up for addresses above 4 
> GB?

You mean that an IOMMU could allocate an address above 4GB wrongly? If
so, IIRC, all the IOMMU implementations use dev->dma_mask and
dev->coherent_dma_mask properly. And the DMA address space of the
majority of IOMMUs are limited less than 4GB.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/