On Mon, 19 Oct 2020 08:57:03 +0000 Joel Stanley wrote:

quoted

diff --git a/drivers/net/ethernet/faraday/ftgmac100.c b/drivers/net/ethernet/faraday/ftgmac100.c
index 00024dd41147..9a99a87f29f3 100644
--- a/drivers/net/ethernet/faraday/ftgmac100.c
+++ b/drivers/net/ethernet/faraday/ftgmac100.c

@@ -804,7 +804,8 @@ static netdev_tx_t ftgmac100_hard_start_xmit(struct sk_buff *skb,
         * before setting the OWN bit on the first descriptor.
         */
        dma_wmb();
-       first->txdes0 = cpu_to_le32(f_ctl_stat);
+       WRITE_ONCE(first->txdes0, cpu_to_le32(f_ctl_stat));
+       READ_ONCE(first->txdes0);  

I understand what you're trying to do here, but I'm not sure that this
is the correct way to go about it.

It does cause the compiler to produce a store and then a load.

+1 @first is system memory from dma_alloc_coherent(), right?

You shouldn't have to do this. Is coherent DMA memory broken 
on your platform?