[PATCH net-next 1/3] net: dsa: microchip: ksz9477: apply a shorter ageing time at once

[Oleksij Rempel]

On a KSZ9893 a new Age Period applies only after the running one has
ended, and an entry keeps the Age Count it was stored with. When the
bridge shortens the ageing time for an STP topology change, stale
entries outlive the topology change: 61 to 79 s were measured at
forward_delay 4 s, where the bridge asks for 8 s.

Pulse Fast Aging when the programmed ageing time gets shorter or the Age
Count smaller. On a KSZ9893 it removed the dynamic entries of the user
ports and started the new period at once; 2 ms was enough, the datasheet
gives no pulse length.

Tested on a KSZ9893 with kernel STP. Other chips using this function
were not tested.

Signed-off-by: Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx>
---
 drivers/net/dsa/microchip/ksz9477.c | 36 ++++++++++++++++++++++++++++++++----
 1 file changed, 32 insertions(+), 4 deletions(-)

diff --git a/drivers/net/dsa/microchip/ksz9477.c b/drivers/net/dsa/microchip/ksz9477.c
index 72528a53b67d2d269d9a0505b0cc0c2348f06fad..b54f388b227f19c58c35ce3642935387c11e9356 100644
--- a/drivers/net/dsa/microchip/ksz9477.c
+++ b/drivers/net/dsa/microchip/ksz9477.c
@@ -1289,13 +1289,16 @@ static void ksz9477_phylink_get_caps(struct dsa_switch *ds, int port,
 	ksz_phylink_get_caps(ds, port, config);
 }
 
+/* No pulse length in the datasheet; this one worked on a KSZ9893. */
+#define KSZ9477_FAST_AGE_PULSE_US	(2 * USEC_PER_MSEC)
+
 static int ksz9477_set_ageing_time(struct dsa_switch *ds, unsigned int msecs)
 {
 	struct ksz_device *dev = ds->priv;
+	u8 data, mult, value, old_period;
+	u32 old_secs, new_secs, max_val;
 	u32 secs = msecs / 1000;
-	u8 data, mult, value;
-	u32 max_val;
-	int ret;
+	int ret, err;
 
 #define MAX_TIMER_VAL	((1 << 8) - 1)
 
@@ -1314,8 +1317,13 @@ static int ksz9477_set_ageing_time(struct dsa_switch *ds, unsigned int msecs)
 	if (ret < 0)
 		return ret;
 
+	ret = ksz_read8(dev, REG_SW_LUE_CTRL_3, &old_period);
+	if (ret < 0)
+		return ret;
+
 	/* Check whether there is need to update the multiplier. */
 	mult = FIELD_GET(SW_AGE_CNT_M, value);
+	old_secs = mult * old_period;
 	max_val = MAX_TIMER_VAL;
 	if (mult > 0) {
 		/* Try to use the same multiplier already in the register as
@@ -1337,7 +1345,27 @@ static int ksz9477_set_ageing_time(struct dsa_switch *ds, unsigned int msecs)
 	}
 
 	value = DIV_ROUND_UP(secs, data);
-	return ksz_write8(dev, REG_SW_LUE_CTRL_3, value);
+	ret = ksz_write8(dev, REG_SW_LUE_CTRL_3, value);
+	if (ret < 0)
+		return ret;
+
+	/* On a KSZ9893 a new period applies only when the running one ends,
+	 * and entries keep the Age Count they were stored with. If the total
+	 * time or the Age Count got smaller, pulse Fast Aging; on a KSZ9893
+	 * that removed the dynamic entries and started the new period.
+	 */
+	new_secs = data * value;
+	if (new_secs >= old_secs && data >= mult)
+		return 0;
+
+	ret = ksz_rmw8(dev, REG_SW_LUE_CTRL_1, SW_FAST_AGING, SW_FAST_AGING);
+	if (!ret)
+		fsleep(KSZ9477_FAST_AGE_PULSE_US);
+
+	/* Clear the bit even after an error. */
+	err = ksz_rmw8(dev, REG_SW_LUE_CTRL_1, SW_FAST_AGING, 0);
+
+	return ret ?: err;
 }
 
 void ksz9477_port_queue_split(struct ksz_device *dev, int port)

-- 
2.47.3