[PATCH 5.8 107/124] net: mscc: ocelot: divide watermark value by 60 when writing to SYS_ATOP

[Greg Kroah-Hartman]

From: Vladimir Oltean <vladimir.olt...@nxp.com>

[ Upstream commit 601e984f23abcaa7cf3eb078c13de4db3cf6a4f0 ]

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.olt...@nxp.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Sasha Levin <sas...@kernel.org>
---
 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 1438839e3f6ea..61bbb7a090042 100644
--- a/drivers/net/ethernet/mscc/ocelot.c
+++ b/drivers/net/ethernet/mscc/ocelot.c
@@ -2001,7 +2001,7 @@ 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;
@@ -2022,12 +2022,12 @@ void ocelot_port_set_maxlen(struct ocelot *ocelot, int 
port, size_t sdu)
        ocelot_rmw_rix(ocelot, SYS_PAUSE_CFG_PAUSE_STOP(pause_stop),
                       SYS_PAUSE_CFG_PAUSE_STOP_M, SYS_PAUSE_CFG, port);
 
-       /* 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