Hi David, On Wednesday 09 May 2007, David Brownell wrote: > On Wednesday 09 May 2007, Laurent Pinchart wrote: > > I wasn't aware of those functions. Just to make sure I get this right, am > > I right to say that URB buffers should be allocated as contiguous cache > > coherent physical memory (using usb_buffer_alloc, which in turns call > > dma_alloc_coherent for big DMAable buffers) > > Not many applications need cache-coherent buffers. > Few of them involve "big" transfers. > > > or as normal memory using scatter-gather routines ? > > Likewise not many stacks hand you scatterlists. If you > get a scatterlist, there's no real option about how to > do that I/O: either dma map yourself, or let usbcore > handle it for you (using the usb_sg_* calls) > > > I currently allocate big bulk buffers using usb_buffer_alloc, which puts > > a lot of pressure on the memory allocator. > > Bad answer, unless you really need that kind of buffer. > From what you've said, you don't need them, and should > not use those allocator calls.
Could you elaborate a bit on the subject ? Which allocator calls should I use ? Just kmalloc ? When does a USB driver need cache coherent buffers ? > > Using scatter-gather mappings would > > help. However, if I'm not mistaken, the usb_sg_* routines are designed > > for synchronous use (with usb_sg_wait), and thus can't be used for > > streaming data. > > Right. Scatterlists come from the block layer, which > doesn't stream. Thanks for your help. Laurent Pinchart ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
