On Tue, Jan 15, 2019 at 04:47:47PM +0100, Lorenzo Bianconi wrote: > Hi Stanislaw, Hi :-) > > Not sure what is the problem , but this patch set look like a workaround > > not fix. If this an issue with IOMMU and sg, seems there is something wrong > > in sg page mappings eigher on mt76 dirver or IOMMU driver. > > The main point here I guess is we do not need sg if fragment number is one (e.g > usb2.0). Moreover this can fix IOMMU reported issues. So there if diffrence for USB host driver when we have one usb->sg sengment and if we just pass the buffer via urb->transfer_buf . I think most USB host drivers behave the same in such cases. For what USB hardware/driver this is needed ? Perhaps simpler fix could be done in USB host driver? Also I'm not sure for what this new module parameter is needed ? > @Rosen: could you please try this series enabling IOMMU? > > > > > If things need to be fixed in mt76 I whould check if page mappings for > > sg are correct. Or remove sg usage from mt76_usb completly, mt76 MMIO > > version do not use sg for framgments, so most likely USB don't need it > > as well. > > usb scatter-gather is used to properly support non-linear skbs (A-MSDU, > with usb3.0) since the hw (unlike pci counterpart) does not support it, > so we need it. Ok, having separe URB for each fragment make no sense since we have embedded sg structure in URB. Regards Stanislaw
