path: root/drivers/net
diff options
authorVladimir Oltean <olteanv@gmail.com>2020-01-04 02:37:09 +0200
committerDavid S. Miller <davem@davemloft.net>2020-01-05 15:13:12 -0800
commit0a51826c6e05c5b6cc423b376b81c311e9e485b0 (patch)
treeda44bcc48f616410d04f10c11cce8fbf16a5bf58 /drivers/net
parentMerge branch 'Fix-10G-PHY-interface-types' (diff)
net: dsa: sja1105: Always send through management routes in slot 0
I finally found out how the 4 management route slots are supposed to be used, but.. it's not worth it. The description from the comment I've just deleted in this commit is still true: when more than 1 management slot is active at the same time, the switch will match frames incoming [from the CPU port] on the lowest numbered management slot that matches the frame's DMAC. My issue was that one was not supposed to statically assign each port a slot. Yes, there are 4 slots and also 4 non-CPU ports, but that is a mere coincidence. Instead, the switch can be used like this: every management frame gets a slot at the right of the most recently assigned slot: Send mgmt frame 1 through S0: S0 x x x Send mgmt frame 2 through S1: S0 S1 x x Send mgmt frame 3 through S2: S0 S1 S2 x Send mgmt frame 4 through S3: S0 S1 S2 S3 The difference compared to the old usage is that the transmission of frames 1-4 doesn't need to wait until the completion of the management route. It is safe to use a slot to the right of the most recently used one, because by protocol nobody will program a slot to your left and "steal" your route towards the correct egress port. So there is a potential throughput benefit here. But mgmt frame 5 has no more free slot to use, so it has to wait until _all_ of S0, S1, S2, S3 are full, in order to use S0 again. And that's actually exactly the problem: I was looking for something that would bring more predictable transmission latency, but this is exactly the opposite: 3 out of 4 frames would be transmitted quicker, but the 4th would draw the short straw and have a worse worst-case latency than before. Useless. Things are made even worse by PTP TX timestamping, which is something I won't go deeply into here. Suffice to say that the fact there is a driver-level lock on the SPI bus offsets any potential throughput gains that parallelism might bring. So there's no going back to the multi-slot scheme, remove the "mgmt_slot" variable from sja1105_port and the dummy static assignment made at probe time. While passing by, also remove the assignment to casc_port altogether. Don't pretend that we support cascaded setups. Signed-off-by: Vladimir Oltean <olteanv@gmail.com> Reviewed-by: Florian Fainelli <f.fainelli@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'drivers/net')
1 files changed, 1 insertions, 25 deletions
diff --git a/drivers/net/dsa/sja1105/sja1105_main.c b/drivers/net/dsa/sja1105/sja1105_main.c
index 1da5ac111499..79dd965227bc 100644
--- a/drivers/net/dsa/sja1105/sja1105_main.c
+++ b/drivers/net/dsa/sja1105/sja1105_main.c
@@ -426,14 +426,6 @@ static int sja1105_init_general_params(struct sja1105_private *priv)
.tpid2 = ETH_P_SJA1105,
struct sja1105_table *table;
- int i, k = 0;
- for (i = 0; i < SJA1105_NUM_PORTS; i++) {
- if (dsa_is_dsa_port(priv->ds, i))
- default_general_params.casc_port = i;
- else if (dsa_is_user_port(priv->ds, i))
- priv->ports[i].mgmt_slot = k++;
- }
table = &priv->static_config.tables[BLK_IDX_GENERAL_PARAMS];
@@ -1827,30 +1819,14 @@ static netdev_tx_t sja1105_port_deferred_xmit(struct dsa_switch *ds, int port,
struct sk_buff *skb)
struct sja1105_private *priv = ds->priv;
- struct sja1105_port *sp = &priv->ports[port];
- int slot = sp->mgmt_slot;
struct sk_buff *clone;
- /* The tragic fact about the switch having 4x2 slots for installing
- * management routes is that all of them except one are actually
- * useless.
- * If 2 slots are simultaneously configured for two BPDUs sent to the
- * same (multicast) DMAC but on different egress ports, the switch
- * would confuse them and redirect first frame it receives on the CPU
- * port towards the port configured on the numerically first slot
- * (therefore wrong port), then second received frame on second slot
- * (also wrong port).
- * So for all practical purposes, there needs to be a lock that
- * prevents that from happening. The slot used here is utterly useless
- * (could have simply been 0 just as fine), but we are doing it
- * nonetheless, in case a smarter idea ever comes up in the future.
- */
/* The clone, if there, was made by dsa_skb_tx_timestamp */
clone = DSA_SKB_CB(skb)->clone;
- sja1105_mgmt_xmit(ds, port, slot, skb, !!clone);
+ sja1105_mgmt_xmit(ds, port, 0, skb, !!clone);
if (!clone)
goto out;