net: mscc: ocelot: divide watermark value by 60 when writing to SYS_ATOP

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>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ethernet/mscc/ocelot.c b/drivers/net/ethernet/mscc/ocelot.c
index 8518e1d..aa002db 100644 (file)
--- 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);