Am Dienstag, 5. Juni 2007 schrieb Pete Zaitcev:
> On Mon, 04 Jun 2007 10:38:44 +0200, Marcel Holtmann <[EMAIL PROTECTED]> wrote:
>
> > static void urb_destroy(struct kref *kref)
> > {
> > struct urb *urb = to_urb(kref);
> > +
> > + if (urb->transfer_flags & URB_FREE_BUFFER)
> > + usb_buffer_free(urb->dev, urb->transfer_buffer_length,
> > + urb->transfer_buffer, urb->transfer_dma);
> > +
> > kfree(urb);
> > }
>
> This looks good to me, although it's useless for the vast majority
> of drivers, because they use kmalloc, or should use kmalloc, but
> use usb_buffer_alloc due to confusion. I'm actually wondering now
> if your driver is one of the latter...
OK, we need to discuss this.
>From Documentation/usb/dma.txt about usb_buffer_alloc():
The memory buffer returned is "dma-coherent"; sometimes you might need to
force a consistent memory access ordering by using memory barriers. It's
not using a streaming DMA mapping, so it's good for small transfers on
systems where the I/O would otherwise tie up an IOMMU mapping. (See
Documentation/DMA-mapping.txt for definitions of "coherent" and "streaming"
void *hcd_buffer_alloc(
struct usb_bus *bus,
size_t size,
gfp_t mem_flags,
dma_addr_t *dma
)
{
struct usb_hcd *hcd = bus_to_hcd(bus);
int i;
/* some USB hosts just use PIO */
if (!bus->controller->dma_mask) {
*dma = ~(dma_addr_t) 0;
return kmalloc(size, mem_flags);
}
for (i = 0; i < HCD_BUFFER_POOLS; i++) {
if (size <= pool_max [i])
return dma_pool_alloc(hcd->pool [i], mem_flags, dma);
}
return dma_alloc_coherent(hcd->self.controller, size, dma, 0);
}
This takes reasonably care of granularity.
So what exactly is the problem? Is the documentation wrong?
Regards
Oliver
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