[PATCH net 0/2] Fix tail dropping watermarks for Ocelot switches

[PATCH net 0/2] Fix tail dropping watermarks for Ocelot switches

[Vladimir Oltean]

This series adds a missing division by 60, and a warning to prevent that
in the future.

Vladimir Oltean (2):
  net: mscc: ocelot: divide watermark value by 60 when writing to
    SYS_ATOP
  net: mscc: ocelot: warn when encoding an out-of-bounds watermark value

 drivers/net/dsa/ocelot/felix_vsc9959.c     |  2 ++
 drivers/net/dsa/ocelot/seville_vsc9953.c   |  2 ++
 drivers/net/ethernet/mscc/ocelot.c         | 12 ++++++------
 drivers/net/ethernet/mscc/ocelot_vsc7514.c |  2 ++
 4 files changed, 12 insertions(+), 6 deletions(-)

-- 
2.25.1

[PATCH net 1/2] net: mscc: ocelot: divide watermark value by 60 when writing to SYS_ATOP

[Vladimir Oltean]

Tail dropping is enabled for a port when:

1. A source port consumes more packet buffers than the watermark encoded
   in SYS:PORT:ATOP_CFG.ATOP.

AND

2. Total memory use exceeds the consumption watermark encoded in
   SYS:PAUSE_CFG:ATOP_TOT_CFG.

The unit of these watermarks is a 60 byte memory cell. That unit is
programmed properly into ATOP_TOT_CFG, but not into ATOP. Actually when
written into ATOP, it would get truncated and wrap around.

Fixes: a556c76adc05 ("net: mscc: Add initial Ocelot switch support")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
---
 drivers/net/ethernet/mscc/ocelot.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/mscc/ocelot.c b/drivers/net/ethernet/mscc/ocelot.c
index e026617d6133..f435dc4d5573 100644
--- a/drivers/net/ethernet/mscc/ocelot.c
+++ b/drivers/net/ethernet/mscc/ocelot.c
@@ -1253,7 +1253,7 @@ void ocelot_port_set_maxlen(struct ocelot *ocelot, int port, size_t sdu)
 	struct ocelot_port *ocelot_port = ocelot->ports[port];
 	int maxlen = sdu + ETH_HLEN + ETH_FCS_LEN;
 	int pause_start, pause_stop;
-	int atop_wm;
+	int atop, atop_tot;
 
 	if (port == ocelot->npi) {
 		maxlen += OCELOT_TAG_LEN;
@@ -1274,12 +1274,12 @@ void ocelot_port_set_maxlen(struct ocelot *ocelot, int port, size_t sdu)
 	ocelot_fields_write(ocelot, port, SYS_PAUSE_CFG_PAUSE_STOP,
 			    pause_stop);
 
-	/* Tail dropping watermark */
-	atop_wm = (ocelot->shared_queue_sz - 9 * maxlen) /
+	/* Tail dropping watermarks */
+	atop_tot = (ocelot->shared_queue_sz - 9 * maxlen) /
 		   OCELOT_BUFFER_CELL_SZ;
-	ocelot_write_rix(ocelot, ocelot->ops->wm_enc(9 * maxlen),
-			 SYS_ATOP, port);
-	ocelot_write(ocelot, ocelot->ops->wm_enc(atop_wm), SYS_ATOP_TOT_CFG);
+	atop = (9 * maxlen) / OCELOT_BUFFER_CELL_SZ;
+	ocelot_write_rix(ocelot, ocelot->ops->wm_enc(atop), SYS_ATOP, port);
+	ocelot_write(ocelot, ocelot->ops->wm_enc(atop_tot), SYS_ATOP_TOT_CFG);
 }
 EXPORT_SYMBOL(ocelot_port_set_maxlen);
 
-- 
2.25.1

[PATCH net 2/2] net: mscc: ocelot: warn when encoding an out-of-bounds watermark value

[Vladimir Oltean]

There is an upper bound to the value that a watermark may hold. That
upper bound is not immediately obvious during configuration, and it
might be possible to have accidental truncation.

Actually this has happened already, add a warning to prevent it from
happening again.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
---
 drivers/net/dsa/ocelot/felix_vsc9959.c     | 2 ++
 drivers/net/dsa/ocelot/seville_vsc9953.c   | 2 ++
 drivers/net/ethernet/mscc/ocelot_vsc7514.c | 2 ++
 3 files changed, 6 insertions(+)

diff --git a/drivers/net/dsa/ocelot/felix_vsc9959.c b/drivers/net/dsa/ocelot/felix_vsc9959.c
index 4fc67ff212de..cb0f3d28ecac 100644
--- a/drivers/net/dsa/ocelot/felix_vsc9959.c
+++ b/drivers/net/dsa/ocelot/felix_vsc9959.c
@@ -998,6 +998,8 @@ static int vsc9959_prevalidate_phy_mode(struct ocelot *ocelot, int port,
  */
 static u16 vsc9959_wm_enc(u16 value)
 {
+	WARN_ON(value >= 16 * BIT(8));
+
 	if (value >= BIT(8))
 		return BIT(8) | (value / 16);
 
diff --git a/drivers/net/dsa/ocelot/seville_vsc9953.c b/drivers/net/dsa/ocelot/seville_vsc9953.c
index e993f3eac3eb..76576cf0ba8a 100644
--- a/drivers/net/dsa/ocelot/seville_vsc9953.c
+++ b/drivers/net/dsa/ocelot/seville_vsc9953.c
@@ -1049,6 +1049,8 @@ static int vsc9953_prevalidate_phy_mode(struct ocelot *ocelot, int port,
  */
 static u16 vsc9953_wm_enc(u16 value)
 {
+	WARN_ON(value >= 16 * BIT(9));
+
 	if (value >= BIT(9))
 		return BIT(9) | (value / 16);
 
diff --git a/drivers/net/ethernet/mscc/ocelot_vsc7514.c b/drivers/net/ethernet/mscc/ocelot_vsc7514.c
index f3e54589e6d6..79b88bc69c75 100644
--- a/drivers/net/ethernet/mscc/ocelot_vsc7514.c
+++ b/drivers/net/ethernet/mscc/ocelot_vsc7514.c
@@ -754,6 +754,8 @@ static int ocelot_reset(struct ocelot *ocelot)
  */
 static u16 ocelot_wm_enc(u16 value)
 {
+	WARN_ON(value >= 16 * BIT(8));
+
 	if (value >= BIT(8))
 		return BIT(8) | (value / 16);
 
-- 
2.25.1

Re: [PATCH net 0/2] Fix tail dropping watermarks for Ocelot switches

[David Miller]

From: Vladimir Oltean <vladimir.oltean@nxp.com>
Date: Mon,  5 Oct 2020 12:09:10 +0300

> This series adds a missing division by 60, and a warning to prevent that
> in the future.

Series applied, thank you.