On Saturday 29 July 2006 1:37 pm, Alan Stern wrote:
> On Fri, 28 Jul 2006, Pete Zaitcev wrote:
>
> > Why do we even have this bus operation method?
>
> It's documented in usb.c:usb_buffer_alloc. Obviously the idea is to map a
> frequently-used DMA buffer just once instead of over and over.
Erm, no ... buffer allocation and buffer mapping are distinct operations,
that one only affects allocation.
Note by the way that recent kernels added a new dma operation:
dma_mapping_error(dma_addr_t)
returns boolean ... finally, it's at least possible to report mapping
errors, alhough the invalid DMA address is still arch-specific (and usually
all-ones).
> Are you asking why the method is per-bus? I don't know; the current
> implementation doesn't use this feature.
At least sl811-hcd could use it, and in general the dma issues need
to be tied to the underlying usb_bus not a usb_device since that's how
the operations work.
- Dave
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