On Tue, Sep 01, 2020 at 07:12:41PM +0200, Thomas Bogendoerfer wrote:
> On Tue, Sep 01, 2020 at 05:22:09PM +0200, Thomas Bogendoerfer wrote:
> > On Wed, Aug 19, 2020 at 08:55:49AM +0200, Christoph Hellwig wrote:
> > > Use the proper modern API to transfer cache ownership for incoherent DMA.
> > >
> > > Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> > > ---
> > > drivers/net/ethernet/seeq/sgiseeq.c | 12 ++++++++----
> > > 1 file changed, 8 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/net/ethernet/seeq/sgiseeq.c b/drivers/net/ethernet/seeq/sgiseeq.c
> > > index 39599bbb5d45b6..f91dae16d69a19 100644
> > > --- a/drivers/net/ethernet/seeq/sgiseeq.c
> > > +++ b/drivers/net/ethernet/seeq/sgiseeq.c
> > > @@ -112,14 +112,18 @@ struct sgiseeq_private {
> > >
> > > static inline void dma_sync_desc_cpu(struct net_device *dev, void *addr)
> > > {
> > > - dma_cache_sync(dev->dev.parent, addr, sizeof(struct sgiseeq_rx_desc),
> > > - DMA_FROM_DEVICE);
> > > + struct sgiseeq_private *sp = netdev_priv(dev);
> > > +
> > > + dma_sync_single_for_cpu(dev->dev.parent, VIRT_TO_DMA(sp, addr),
> > > + sizeof(struct sgiseeq_rx_desc), DMA_BIDIRECTIONAL);
> > > }
> > >
> > > static inline void dma_sync_desc_dev(struct net_device *dev, void *addr)
> > > {
> > > - dma_cache_sync(dev->dev.parent, addr, sizeof(struct sgiseeq_rx_desc),
> > > - DMA_TO_DEVICE);
> > > + struct sgiseeq_private *sp = netdev_priv(dev);
> > > +
> > > + dma_sync_single_for_device(dev->dev.parent, VIRT_TO_DMA(sp, addr),
> > > + sizeof(struct sgiseeq_rx_desc), DMA_BIDIRECTIONAL);
> > > }
> >
> > this breaks ethernet on IP22 completely, but I haven't figured out why, yet.
>
> the problem is that dma_sync_single_for_cpu() doesn't flush anything
> for IP22, because it only flushes for CPUs which do speculation. So
> either MIPS arch_sync_dma_for_cpu() should always flush or sgiseeq
> needs to use a different sync funktion, when it wants to re-read descriptors
> from memory.
Well, if IP22 doesn't speculate (which I'm pretty sure is the case),
dma_sync_single_for_cpu should indeeed be a no-op. But then there
also shouldn't be anything in the cache, as the previous
dma_sync_single_for_device should have invalidated it. So it seems like
we are missing one (or more) ownership transfers to the device. I'll
try to look at the the ownership management in a little more detail
tomorrow.
