> On Tue, Feb 12, 2019 at 03:09:53PM +0100, Lorenzo Bianconi wrote:
> > >
> > > (repost with corrected Lorenzo email)
> > >
> > > On Tue, Feb 12, 2019 at 02:45:50PM +0100, Stanislaw Gruszka wrote:
> > > > On Tue, Feb 12, 2019 at 02:24:47PM +0100, LorenzoBianconilorenzo@xxxxxxxxxx wrote:
> > > > > From: Lorenzo Bianconi <lorenzo@xxxxxxxxxx>
> > > > >
> > > > > Use linear fragment and not a single usb scatter-gather buffer in mt76u
> > > > > {tx,rx} datapath if the usb controller has sg data length constraints.
> > > > > Moreover add disable_usb_sg module parameter in order to explicitly
> > > > > disable scatter-gather. SG I/O is not supported by all host drivers and
> > > > > some users have reported sg issues on AMD IOMMU.
> > > >
> > > > Again. This is not right approach. SG issues should be fixed
> > > > not workarounded.
> >
> > Hi Stanislaw,
> >
> > here we do not use SG, so num_sg is 0 and we use transfer_buffer. I do
> > not see how I am working around the issue.
>
> By avoiding SG buffer allocation and configuration which most likely
> need to be fixed.
In my series I:
1- set num_sg to 0
2- use transfer_buffer
please correct me if I am wrong but in your solution you did the same since AFAIK
PageHighMem is always 0 so you end up setting num_sg to 0 and using
transfer_buffer as well. Is my understanding correct?
>
> > Moreover with this approach we avoid some unnecessary operation in the hotpath
>
> What unnecessary operation ?
the ones in mt76u_fill_bulk_urb()
Regards,
Lorenzo
>
> Stanislaw
