| Message ID | 20210510110708.11504-1-michael@walle.cc (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 297c4de6f780b63b6d2af75a730720483bf1904a |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [net] net: dsa: felix: re-enable TAS guard band mode | expand |
| Context | Check | Description |
|---|---|---|
| netdev/cover_letter | success | Link |
| netdev/fixes_present | success | Link |
| netdev/patch_count | success | Link |
| netdev/tree_selection | success | Clearly marked for net |
| netdev/subject_prefix | success | Link |
| netdev/cc_maintainers | success | CCed 11 of 11 maintainers |
| netdev/source_inline | success | Was 0 now: 0 |
| netdev/verify_signedoff | success | Link |
| netdev/module_param | success | Was 0 now: 0 |
| netdev/build_32bit | success | Errors and warnings before: 0 this patch: 0 |
| netdev/kdoc | success | Errors and warnings before: 0 this patch: 0 |
| netdev/verify_fixes | success | Link |
| netdev/checkpatch | success | total: 0 errors, 0 warnings, 0 checks, 22 lines checked |
| netdev/build_allmodconfig_warn | success | Errors and warnings before: 0 this patch: 0 |
| netdev/header_inline | success | Link |
On Mon, May 10, 2021 at 01:07:08PM +0200, Michael Walle wrote: > 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>
Hello: This patch was applied to netdev/net.git (refs/heads/master): On Mon, 10 May 2021 13:07:08 +0200 you wrote: > 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. > > [...] Here is the summary with links: - [net] net: dsa: felix: re-enable TAS guard band mode https://git.kernel.org/netdev/net/c/297c4de6f780 You are awesome, thank you! -- Deet-doot-dot, I am a bot. https://korg.docs.kernel.org/patchwork/pwbot.html
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);
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> --- drivers/net/dsa/ocelot/felix_vsc9959.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-)