Re: [PATCH] arm64: Enable PCI write-combine resources under sysfs

Jason Gunthorpe
2020-09-14T14:38:51Z

On Mon, Sep 14, 2020 at 02:24:06PM +0000, Clint Sbisa wrote:
> On Mon, Sep 14, 2020 at 11:17:26AM -0300, Jason Gunthorpe wrote:
> > On Fri, Sep 11, 2020 at 09:42:25PM +0000, Clint Sbisa wrote:
> >
> > > There's no DMA involved with this BAR-- the driver writes a portion of the
> > > packet contents in addition to the descriptors, which generally increases the
> > > number of TLPs if write-combine isn't used. Furthermore, this BAR is only used
> > > for writes and never for reads.
> >
> > You use DPDK without DMA? How does receive work?
>
> That was not worded well. DMA is used, but the first X bytes of the packet are
> written directly to this BAR instead of being DMA'd-- the rest of the data is
> DMA'd.

which is back to my original question, how do you do DMA using
/sys/xx/resources? Why not use VFIO like everything else?

Jason