Re: [PATCH 22/28] sgiseeq: convert from dma_cache_sync to dma_sync_single_for_device

On Thu, Sep 03, 2020 at 10:43:02AM +0200, Christoph Hellwig wrote:

On Tue, Sep 01, 2020 at 07:38:10PM +0200, Thomas Bogendoerfer wrote:

quoted

this is the problem:

       /* Always check for received packets. */
        sgiseeq_rx(dev, sp, hregs, sregs);

so the driver will look at the rx descriptor on every interrupt, so
we cache the rx descriptor on the first interrupt and if there was
$no rx packet, we will only see it, if cache line gets flushed for
some other reason.

That means a transfer back to device ownership is missing after a
(negative) check.

E.g. something like this for the particular problem, although there
might be other hiding elsewhere:

diff --git a/drivers/net/ethernet/seeq/sgiseeq.c b/drivers/net/ethernet/seeq/sgiseeq.c
index 8507ff2420143a..a1c7be8a0d1e5d 100644
--- a/drivers/net/ethernet/seeq/sgiseeq.c
+++ b/drivers/net/ethernet/seeq/sgiseeq.c

@@ -403,6 +403,8 @@ static inline void sgiseeq_rx(struct net_device *dev, struct sgiseeq_private *sp
 		rd = &sp->rx_desc[sp->rx_new];
 		dma_sync_desc_cpu(dev, rd);
 	}
+	dma_sync_desc_dev(dev, rd);
+
 	dma_sync_desc_cpu(dev, &sp->rx_desc[orig_end]);
 	sp->rx_desc[orig_end].rdma.cntinfo &= ~(HPCDMA_EOR);
 	dma_sync_desc_dev(dev, &sp->rx_desc[orig_end]);