net: mscc: ocelot: add ops for decoding watermark threshold and occupancy

We'll need to read back the watermark thresholds and occupancy from
hardware (for devlink-sb integration), not only to write them as we did
so far in ocelot_port_set_maxlen. So introduce 2 new functions in struct
ocelot_ops, similar to wm_enc, and implement them for the 3 supported
mscc_ocelot switches.

Remove the INUSE and MAXUSE unpacking helpers for the QSYS_RES_STAT
register, because that doesn't scale with the number of switches that
mscc_ocelot supports now. They have different bit widths for the
watermarks, and we need function pointers to abstract that difference
away.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/dsa/ocelot/felix_vsc9959.c

@@ -1006,9 +1006,27 @@ static u16 vsc9959_wm_enc(u16 value)
 	return value;
 }
 
+static u16 vsc9959_wm_dec(u16 wm)
+{
+	WARN_ON(wm & ~GENMASK(8, 0));
+
+	if (wm & BIT(8))
+		return (wm & GENMASK(7, 0)) * 16;
+
+	return wm;
+}
+
+static void vsc9959_wm_stat(u32 val, u32 *inuse, u32 *maxuse)
+{
+	*inuse = (val & GENMASK(23, 12)) >> 12;
+	*maxuse = val & GENMASK(11, 0);
+}
+
 static const struct ocelot_ops vsc9959_ops = {
 	.reset			= vsc9959_reset,
 	.wm_enc			= vsc9959_wm_enc,
+	.wm_dec			= vsc9959_wm_dec,
+	.wm_stat		= vsc9959_wm_stat,
 	.port_to_netdev		= felix_port_to_netdev,
 	.netdev_to_port		= felix_netdev_to_port,
 };

drivers/net/dsa/ocelot/seville_vsc9953.c

@@ -1057,9 +1057,27 @@ static u16 vsc9953_wm_enc(u16 value)
 	return value;
 }
 
+static u16 vsc9953_wm_dec(u16 wm)
+{
+	WARN_ON(wm & ~GENMASK(9, 0));
+
+	if (wm & BIT(9))
+		return (wm & GENMASK(8, 0)) * 16;
+
+	return wm;
+}
+
+static void vsc9953_wm_stat(u32 val, u32 *inuse, u32 *maxuse)
+{
+	*inuse = (val & GENMASK(25, 13)) >> 13;
+	*maxuse = val & GENMASK(12, 0);
+}
+
 static const struct ocelot_ops vsc9953_ops = {
 	.reset			= vsc9953_reset,
 	.wm_enc			= vsc9953_wm_enc,
+	.wm_dec			= vsc9953_wm_dec,
+	.wm_stat		= vsc9953_wm_stat,
 	.port_to_netdev		= felix_port_to_netdev,
 	.netdev_to_port		= felix_netdev_to_port,
 };