Messages in this thread | | | Subject | Re: [PATCH v2 1/2] net: nps_enet: Sync access to packet sent flag | From | Lino Sanfilippo <> | Date | Tue, 10 May 2016 20:32:49 +0200 |
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Hi Elad,
On 08.05.2016 15:44, Elad Kanfi wrote:
> > After reviewing the code and your suggestion, it seems that we can do without the flag tx_packet_sent and therefor the first issue becomes irrelevant. > The indication that a packet was sent is (tx_skb != NULL) , and the sequence will be: > > CPU A: > 1. tx_skb = skb > 2. wmb() /* make sure tx_skb reaches the RAM before the HW is informed and the IRQ is fired */ > 3. nps_enet_reg_set(priv, NPS_ENET_REG_TX_CTL, tx_ctrl.value); /* send frame */ > > CPU B: > 1. read tx_skb > 2. if( tx_skb != NULL ) handle tx_skb > 3. tx_skb = NULL > >
Ok, without the tx_packet_sent flag the code becomes simpler. But it does not mean that we can toss the smp_rmb in the irq handler completely. We still have to use a read barrier there to ensure that we see the most recent value of tx_skb. E.g like this:
if (priv->tx_skb != NULL ) { smp_rmb() / * handle tx_skb */ }
With both barriers in place the code should work as expected.
Regards, Lino
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