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Message-ID: <3232ef43-d568-0851-4511-6fe7c86d9e8a@gmail.com> Date: Fri, 3 May 2019 19:07:37 -0700 From: Florian Fainelli <f.fainelli@...il.com> To: Vladimir Oltean <olteanv@...il.com>, vivien.didelot@...il.com, andrew@...n.ch, davem@...emloft.net Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH net-next 5/9] net: dsa: Add support for deferred xmit On 5/3/2019 6:18 PM, Vladimir Oltean wrote: > Some hardware needs to take some convincing work in order to receive > frames on the CPU port (such as the sja1105 which takes temporary L2 > forwarding rules over SPI that last for a single frame). Such work needs > a sleepable context, and because the regular .ndo_start_xmit is atomic, > this cannot be done in the tagger. So introduce a generic DSA mechanism > that sets up a transmit skb queue and a workqueue for deferred > transmission. > > The new driver callback (.port_deferred_xmit) is in dsa_switch and not > in the tagger because the operations that require sleeping typically > also involve interacting with the hardware, and not simply skb > manipulations. Therefore having it there simplifies the structure a bit > and makes it unnecessary to export functions from the driver to the > tagger. > > The driver is responsible of calling dsa_enqueue_skb which transfers it > to the master netdevice. This is so that it has a chance of performing > some more work afterwards, such as cleanup or TX timestamping. > > To tell DSA that skb xmit deferral is required, I have thought about > changing the return type of the tagger .xmit from struct sk_buff * into > a enum dsa_tx_t that could potentially encode a DSA_XMIT_DEFER value. > > But the trailer tagger is reallocating every skb on xmit and therefore > making a valid use of the pointer return value. So instead of reworking > the API in complicated ways, right now a boolean property in the newly > introduced DSA_SKB_CB is set. > > Signed-off-by: Vladimir Oltean <olteanv@...il.com> > --- [snip] > static inline struct dsa_port *dsa_slave_to_port(const struct net_device *dev) > { > struct dsa_slave_priv *p = netdev_priv(dev); > diff --git a/net/dsa/slave.c b/net/dsa/slave.c > index 8ad9bf957da1..cfb8cba6458c 100644 > --- a/net/dsa/slave.c > +++ b/net/dsa/slave.c > @@ -120,6 +120,9 @@ static int dsa_slave_close(struct net_device *dev) > struct net_device *master = dsa_slave_to_master(dev); > struct dsa_port *dp = dsa_slave_to_port(dev); > > + cancel_work_sync(&dp->xmit_work); > + skb_queue_purge(&dp->xmit_queue); > + > phylink_stop(dp->pl); Don't you also need to do that for dsa_slave_suspend() in case the xmit() raced with netif_device_detach() somehow? -- Florian
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