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Date: Sun, 30 Nov 2014 11:27:48 -0800 From: Eric Dumazet <eric.dumazet@...il.com> To: Wei Yang <weiyang@...ux.vnet.ibm.com> Cc: netdev@...r.kernel.org, davem@...emloft.net, gideonn@...lanox.com, Eric Dumazet <edumazet@...gle.com>, Amir Vadai <amirv@...lanox.com> Subject: Re: [PATCH net] net/mlx4_en: correct the endianness of doorbell_qpn on big endian platform On Sun, 2014-11-30 at 10:43 +0800, Wei Yang wrote: > In commit 6a4e812 (net/mlx4_en: Avoid calling bswap in tx fast path), we store > doorbell_qpn in big endian to avoid bswap(). Then we try to write it directly > by iowrite32() instead of iowrite32be(). > > This works fine on little endian platform, while has some problem on big > endian platform. Here is the definition in general: > > #define iowrite32(v, addr) writel((v), (addr)) > #define writel(b,addr) __raw_writel(__cpu_to_le32(b),addr) Oh well... > > On little endian platform, the value is not swapped before write. While on big > endian platform, the value is swapped. This is not expected to happen. > > This patch does the swap on big endian platform before it is written. > > Signed-off-by: Wei Yang <weiyang@...ux.vnet.ibm.com> > CC: Eric Dumazet <edumazet@...gle.com> > CC: Amir Vadai <amirv@...lanox.com> > --- > drivers/net/ethernet/mellanox/mlx4/en_tx.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/net/ethernet/mellanox/mlx4/en_tx.c b/drivers/net/ethernet/mellanox/mlx4/en_tx.c > index 454d9fe..76f028b 100644 > --- a/drivers/net/ethernet/mellanox/mlx4/en_tx.c > +++ b/drivers/net/ethernet/mellanox/mlx4/en_tx.c > @@ -954,7 +954,7 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev) > tx_desc->ctrl.owner_opcode = op_own; > if (send_doorbell) { > wmb(); > - iowrite32(ring->doorbell_qpn, > + iowrite32(__cpu_to_le32(ring->doorbell_qpn), > ring->bf.uar->map + MLX4_SEND_DOORBELL); > } else { > ring->xmit_more++; Well, whole idea of the patch was to perform the swap (if any) out of the fast path. ring->doorbell_qpn is a cache of whatever value. Have you tried to convert it to a __le32 instead of __be32 ? Thanks -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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