diff options
| author | Michael Walle <michael@walle.cc> | 2021-05-10 14:07:08 +0300 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2021-05-11 00:48:55 +0300 |
| commit | 297c4de6f780b63b6d2af75a730720483bf1904a (patch) | |
| tree | 9f7dcaf0f48517ba958bd9e88c8f4ac54bf863b1 /drivers/net/dsa | |
| parent | 3058e01d31bbdbe50e02cafece2b22817a6a0eae (diff) | |
| download | linux-297c4de6f780b63b6d2af75a730720483bf1904a.tar.xz | |
net: dsa: felix: re-enable TAS guard band mode
Commit 316bcffe4479 ("net: dsa: felix: disable always guard band bit for
TAS config") disabled the guard band and broke 802.3Qbv compliance.
There are two issues here:
(1) Without the guard band the end of the scheduling window could be
overrun by a frame in transit.
(2) Frames that don't fit into a configured window will still be sent.
The reason for both issues is that the switch will schedule the _start_
of a frame transmission inside the predefined window without taking the
length of the frame into account. Thus, we'll need the guard band which
will close the gate early, so that a complete frame can still be sent.
Revert the commit and add a note.
For a lengthy discussion see [1].
[1] https://lore.kernel.org/netdev/c7618025da6723418c56a54fe4683bd7@walle.cc/
Fixes: 316bcffe4479 ("net: dsa: felix: disable always guard band bit for TAS config")
Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'drivers/net/dsa')
| -rw-r--r-- | drivers/net/dsa/ocelot/felix_vsc9959.c | 15 |
1 files changed, 10 insertions, 5 deletions
diff --git a/drivers/net/dsa/ocelot/felix_vsc9959.c b/drivers/net/dsa/ocelot/felix_vsc9959.c index 2473bebe48e6..f966a253d1c7 100644 --- a/drivers/net/dsa/ocelot/felix_vsc9959.c +++ b/drivers/net/dsa/ocelot/felix_vsc9959.c @@ -1227,12 +1227,17 @@ static int vsc9959_qos_port_tas_set(struct ocelot *ocelot, int port, if (taprio->num_entries > VSC9959_TAS_GCL_ENTRY_MAX) return -ERANGE; - /* Set port num and disable ALWAYS_GUARD_BAND_SCH_Q, which means set - * guard band to be implemented for nonschedule queues to schedule - * queues transition. + /* Enable guard band. The switch will schedule frames without taking + * their length into account. Thus we'll always need to enable the + * guard band which reserves the time of a maximum sized frame at the + * end of the time window. + * + * Although the ALWAYS_GUARD_BAND_SCH_Q bit is global for all ports, we + * need to set PORT_NUM, because subsequent writes to PARAM_CFG_REG_n + * operate on the port number. */ - ocelot_rmw(ocelot, - QSYS_TAS_PARAM_CFG_CTRL_PORT_NUM(port), + ocelot_rmw(ocelot, QSYS_TAS_PARAM_CFG_CTRL_PORT_NUM(port) | + QSYS_TAS_PARAM_CFG_CTRL_ALWAYS_GUARD_BAND_SCH_Q, QSYS_TAS_PARAM_CFG_CTRL_PORT_NUM_M | QSYS_TAS_PARAM_CFG_CTRL_ALWAYS_GUARD_BAND_SCH_Q, QSYS_TAS_PARAM_CFG_CTRL); |