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Message-ID: <PAXPR04MB91857E7BEC3E199D52E4376E897F9@PAXPR04MB9185.eurprd04.prod.outlook.com> Date: Thu, 18 May 2023 13:33:27 +0000 From: Shenwei Wang <shenwei.wang@....com> To: Heiner Kallweit <hkallweit1@...il.com>, Wei Fang <wei.fang@....com>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, Horatiu Vultur <horatiu.vultur@...rochip.com> CC: Clark Wang <xiaoning.wang@....com>, dl-linux-imx <linux-imx@....com>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "imx@...ts.linux.dev" <imx@...ts.linux.dev> Subject: RE: [EXT] Re: [PATCH v2 net] net: fec: add wmb to ensure correct descriptor values > -----Original Message----- > From: Heiner Kallweit <hkallweit1@...il.com> > Sent: Wednesday, May 17, 2023 2:14 PM > To: Shenwei Wang <shenwei.wang@....com>; Wei Fang <wei.fang@....com>; > David S. Miller <davem@...emloft.net>; Eric Dumazet > <edumazet@...gle.com>; Jakub Kicinski <kuba@...nel.org>; Paolo Abeni > <pabeni@...hat.com>; Simon Horman <horms@...nel.org>; Horatiu Vultur > <horatiu.vultur@...rochip.com> > Cc: Clark Wang <xiaoning.wang@....com>; dl-linux-imx <linux-imx@....com>; > netdev@...r.kernel.org; imx@...ts.linux.dev > Subject: [EXT] Re: [PATCH v2 net] net: fec: add wmb to ensure correct descriptor > values > > Caution: This is an external email. Please take care when clicking links or > opening attachments. When in doubt, report the message using the 'Report this > email' button > > > On 17.05.2023 18:15, Shenwei Wang wrote: > > Two wmb() are added in the XDP TX path to ensure proper ordering of > > descriptor and buffer updates: > > 1. A wmb() is added after updating the last BD to make sure > > the updates to rest of the descriptor are visible before > > transferring ownership to FEC. > > 2. A wmb() is also added after updating the tx_skbuff and bdp > > to ensure these updates are visible before updating txq->bd.cur. > > 3. Start the xmit of the frame immediately right after configuring the > > tx descriptor. > > > > Fixes: 6d6b39f180b8 ("net: fec: add initial XDP support") > > Signed-off-by: Shenwei Wang <shenwei.wang@....com> > > --- > > v2: > > - update the inline comments for 2nd wmb per Wei Fang's review. > > > > drivers/net/ethernet/freescale/fec_main.c | 17 +++++++++++------ > > 1 file changed, 11 insertions(+), 6 deletions(-) > > > > diff --git a/drivers/net/ethernet/freescale/fec_main.c > > b/drivers/net/ethernet/freescale/fec_main.c > > index 6d0b46c76924..d210e67a188b 100644 > > --- a/drivers/net/ethernet/freescale/fec_main.c > > +++ b/drivers/net/ethernet/freescale/fec_main.c > > @@ -3834,6 +3834,11 @@ static int fec_enet_txq_xmit_frame(struct > fec_enet_private *fep, > > index = fec_enet_get_bd_index(last_bdp, &txq->bd); > > txq->tx_skbuff[index] = NULL; > > > > + /* Make sure the updates to rest of the descriptor are performed before > > + * transferring ownership. > > + */ > > + wmb(); > > + > > /* Send it on its way. Tell FEC it's ready, interrupt when done, > > * it's the last BD of the frame, and to put the CRC on the end. > > */ > > @@ -3843,8 +3848,14 @@ static int fec_enet_txq_xmit_frame(struct > fec_enet_private *fep, > > /* If this was the last BD in the ring, start at the beginning again. */ > > bdp = fec_enet_get_nextdesc(last_bdp, &txq->bd); > > > > + /* Make sure the update to bdp are performed before txq->bd.cur. */ > > + wmb(); > > + > > Do you really need wmb() here or would a more light-weight smp_wmb() or > dma_wmb() be sufficient? > In this case, both wmb should be changed to dma_wmb. Regards, Shenwei > > txq->bd.cur = bdp; > > > > + /* Trigger transmission start */ > > + writel(0, txq->bd.reg_desc_active); > > + > > return 0; > > } > > > > @@ -3873,12 +3884,6 @@ static int fec_enet_xdp_xmit(struct net_device > *dev, > > sent_frames++; > > } > > > > - /* Make sure the update to bdp and tx_skbuff are performed. */ > > - wmb(); > > - > > - /* Trigger transmission start */ > > - writel(0, txq->bd.reg_desc_active); > > - > > __netif_tx_unlock(nq); > > > > return sent_frames; > > -- > > 2.34.1 > > > >
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