Alan Stern wrote: > On Mon, 1 Mar 2010, Albert Herranz wrote: > >>> If transfer_buffer_length is 0 then do nothing. >>> Otherwise if num_sgs > 0 then do nothing. >>> Otherwise if URB_NO_TRANSFER_DMA_MAP and transfer_dma >>> are both set (this avoids your HCD_NO_COHERENT_MEM >>> case) then do nothing. >>> >> I see. This case would include the PIO case too (for which dma_handle >> is set to all 1s). > > The test above should be transfer_dma != ~0, not transfer_dma != 0, > since ~0 means the DMA address isn't set. In fact I forgot to > include the PIO case; it should be handled by changing the remaining > tests as follows: > > Otherwise if hcd->self.uses_dma is set then > If this URB doesn't require PIO then call dma_map_single > Otherwise if HCD_LOCAL_MEM is set then call hcd_alloc_coherent > Otherwise do nothing (PIO case). > > Currently "this URB doesn't require PIO" is always true, but in the > future it won't be. > Can this be currently tested? Should I make provisions for this check now too? >> So this assumes that transfer_dma should be set initially to 0 when >> allocating USB buffers for HCD_NO_COHERENT_MEM. > > No, it should be set to ~0, the same as when buffers are allocated for > a PIO-based controller. > This logic now resembles more the one in my v2 proposal although with different formal checks. I think I'll code and post another iteration of the 8/9 patch with your proposed checks and then we can continue further discussion on it. I'll try to add explanatory comments for each check. > Alan Stern > Thanks a lot for your input, Albert -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
