RE: [PATCH v4 4/6] infiniband: cxgb4: Eliminate duplicate barriers on weakly-ordered archs

[Steve Wise]

> > On Mon, Mar 19, 2018 at 10:47:46PM -0400, Sinan Kaya wrote:
> > > Code includes wmb() followed by writel(). writel() already has a
barrier
> on
> > > some architectures like arm64.
> > >
> > > This ends up CPU observing two barriers back to back before executing
> > the
> > > register write.
> > >
> > > Since code already has an explicit barrier call, changing writel() to
> > > writel_relaxed().
> > >
> > > Signed-off-by: Sinan Kaya <okaya@xxxxxxxxxxxxxx>
> > >  drivers/infiniband/hw/cxgb4/t4.h | 14 +++++++-------
> > >  1 file changed, 7 insertions(+), 7 deletions(-)
> > >
> > > diff --git a/drivers/infiniband/hw/cxgb4/t4.h
> > b/drivers/infiniband/hw/cxgb4/t4.h
> > > index 8369c7c..6e5658a 100644
> > > +++ b/drivers/infiniband/hw/cxgb4/t4.h
> > > @@ -457,7 +457,7 @@ static inline void pio_copy(u64 __iomem *dst,
> u64
> > *src)
> > >  	int count = 8;
> > >
> > >  	while (count) {
> > > -		writeq(*src, dst);
> > > +		writeq_relaxed(*src, dst);
> > >  		src++;
> > >  		dst++;
> > >  		count--;
> >
> > This is another case where writes can be re-ordered.. IIRC dst is WC
> > BAR memory, so the NIC should tolerate re-ordering, but Steve will
> > have to ack this.
> >
> 
> Yes, this is WC BAR memory.  The goal is that pio_copy() will enable
write-
> combining this into a single 64B pci-e transaction.
> 


I'd like to see the PPC issue resolved...but

Acked-by: Steve Wise <swise@xxxxxxxxxxxxxxxxxxxxx>