> On Wed, Jan 16, 2019 at 02:40:46PM +0100, Lorenzo Bianconi wrote: > > On Jan 16, Stanislaw Gruszka wrote: > > > On Wed, Jan 16, 2019 at 12:44:33PM +0100, Lorenzo Bianconi wrote: > > > > > 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. > > > > > > But this should not make any difference for underlying low level USB > > > host driver, since we map 1 buffer of the same size, just by using > > > different routines for that. > > > > probably amd iommu has some constraints on sg buffer layout respect to intel > > one, not sure > > > > > > > > > Please not I have not received any confirm that this series fixes the reported issue > > > > yet :) > > > > > > What is reported issue ? > > > > https://marc.info/?l=linux-wireless&m=154716096506037&w=2 > > So, this if for AMD IOMMU issue as I thought initally. For the moment I > thought you are trying to fix some diffrent problem with some > non-standart usb host controler. Why not standard? Most of net usb drivers do not use sg :) > > I still think not using sg is just workaround for the problem not worth > to do, since we have already workaround in form of disabling IOMMU. > Right fix will be fixing AMD IOMMU driver or fix sg usage in mt76-usb > if it does something wrong. I agree with you that this is not strictly a fix for IOMMU issue but I think we could avoid using sg when we are working just with linear skbs. But first I guess we need some feedbacks from users Regards, Lorenzo > > Regards > Stanislaw
