> 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?
According to https://github.com/torvalds/linux/blob/master/drivers/usb/core/hcd.c#L1557 single sg urb and urb with a configured transfer_buf are managed in a different way. Please not I have not received any confirm that this series fixes the reported issue yet :) > > Also I'm not sure for what this new module parameter is needed ? > This is used to disable sg on usb3.0 since it is enabled by default > > @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. In this case each fragment will be mapped independently I guess Regards, Lorenzo > > Regards > Stanislaw
