On 02/04/15 12:34, Laurent Pinchart wrote:

Hi Florian,

On Wednesday 04 February 2015 11:56:58 Florian Echtler wrote:

quoted

On 04.02.2015 11:22, Hans Verkuil wrote:

quoted

On 02/04/15 11:08, Florian Echtler wrote:

quoted

On 04.02.2015 09:08, Hans Verkuil wrote:

quoted

You can also make a version with vmalloc and I'll merge that, and then
you can look more into the DMA issues. That way the driver is merged,
even if it is perhaps not yet optimal, and you can address that part
later.

OK, that sounds sensible, I will try that route. When using
videobuf2-vmalloc, what do I pass back for alloc_ctxs in queue_setup?

vmalloc doesn't need those, so you can just drop any alloc_ctx related
code.

That's what I assumed, however, I'm running into the same problem as
with dma-sg when I switch to vmalloc...?

I don't expect vmalloc to work, as you can't DMA to vmalloc memory directly 
without any IOMMU in the general case (the allocated memory being physically 
fragmented).

dma-sg should work though, but you won't be able to use usb_bulk_msg(). You 
need to create the URBs manually, set their sg and num_sgs fields and submit 
them.

So it works for other usb media drivers because they allocate memory
using kmalloc (and presumably the usb core can DMA to that), and then memcpy
it to the vmalloc-ed buffers?

Anyway Florian, based on Laurent's explanation I think trying to make
dma-sg work seems to be the best solution. And I've learned something
new :-)

Regards,

	Hans

quoted

I've sent a "proper" patch submission again, which has all the other
issues from the previous submission fixed. I'm hoping you can maybe have
a closer look and see if I'm doing anything subtly wrong which causes
both vmalloc and dma-sg to fail while dma-contig works.