Pavel Machek <pa...@ucw.cz> : [...] > Considering the memory barriers... is something like this neccessary > in the via-rhine ?
Yes. > AFAICT... we need a barrier after making sure that descriptor is no > longer owned by DMA (to make sure we don't get stale data in rest of > descriptor)... and we need a barrier before giving the descriptor to > the dma, to make sure DMA engine sees the complete update....? I would not expect stale data while processing a single transmit descriptor as the transmit completion does not use the rest of the descriptor at all in the via-rhine driver. However I agree that transmit descriptors should be read by the cpu with adequate ordering so the dma_rmb() should stay. Same kind of narrative for dma_wmb rhine_rx (s/read/written/ and s/cpu/device/). > diff --git a/drivers/net/ethernet/via/via-rhine.c > b/drivers/net/ethernet/via/via-rhine.c > index ba5c542..3806e72 100644 > --- a/drivers/net/ethernet/via/via-rhine.c > +++ b/drivers/net/ethernet/via/via-rhine.c [...] > @@ -2061,6 +2062,7 @@ static int rhine_rx(struct net_device *dev, int limit) > > if (desc_status & DescOwn) > break; > + dma_rmb(); > I agree with your explanation for this one (late vlan processing in a different word from the same descriptor). -- Ueimor
