RE: [PATCH net] net: hns: Fix the device being used for dma mapping during TX

[Salil Mehta]

> -----Original Message-----
> From: Lino Sanfilippo [mailto:LinoSanfilippo@xxxxxx]
> Sent: Thursday, February 09, 2017 10:25 AM
> To: Salil Mehta
> Cc: davem@xxxxxxxxxxxxx; Salil Mehta; Zhuangyuzeng (Yisen);
> mehta.salil.lnk@xxxxxxxxx; netdev@xxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; Linuxarm; Yankejian (Hackim Yim)
> Subject: Re: [PATCH net] net: hns: Fix the device being used for dma
> mapping during TX
> 
> Hi,
> 
> > From: Kejian Yan <yankejian@xxxxxxxxxx>
> >
> > This patch fixes the device being used to DMA map skb->data.
> > Erroneous device assignment causes the crash when SMMU is enabled.
> > This happens during TX since buffer gets DMA mapped with device
> > correspondign to net_device and gets unmapped using the device
> > related to DSAF.
> >
> > Signed-off-by: Kejian Yan <yankejian@xxxxxxxxxx>
> > Reviewed-by: Yisen Zhuang <yisen.zhuang@xxxxxxxxxx>
> > Signed-off-by: Salil Mehta <salil.mehta@xxxxxxxxxx>
> > ---
> >  drivers/net/ethernet/hisilicon/hns/hns_enet.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/ethernet/hisilicon/hns/hns_enet.c
> b/drivers/net/ethernet/hisilicon/hns/hns_enet.c
> > index 672b646..2b52a12 100644
> > --- a/drivers/net/ethernet/hisilicon/hns/hns_enet.c
> > +++ b/drivers/net/ethernet/hisilicon/hns/hns_enet.c
> > @@ -305,7 +305,7 @@ int hns_nic_net_xmit_hw(struct net_device *ndev,
> >  			struct hns_nic_ring_data *ring_data)
> >  {
> >  	struct hns_nic_priv *priv = netdev_priv(ndev);
> > -	struct device *dev = priv->dev;
> > +	struct device *dev = ring_to_dev(ring_data->ring);
> >  	struct hnae_ring *ring = ring_data->ring;
> >  	struct netdev_queue *dev_queue;
> >  	struct skb_frag_struct *frag;
> > --
> 
> I would say it should be the other way around: Use priv->dev for
> mapping and
> unmapping instead of ring_to_dev().
Yes, you got it right. Ideally, it should be per-port and for
legacy reasons we have it this way. In the current design, we have
SMMU node per-dsaf and I guess we will not land in the right
dma-ops if we use per-netdev platform-device/device right now.

Best regards
Salil
> 
> Regards,
> Lino