net: dsa: b53: fix ageing time for BCM53101

For some reason Broadcom decided that BCM53101 uses 0.5s increments for
the ageing time register, but kept the field width the same [1]. Due to
this, the actual ageing time was always half of what was configured.

Fix this by adapting the limits and value calculation for BCM53101.

So far it looks like this is the only chip with the increased tick
speed:

$ grep -l -r "Specifies the aging time in 0.5 seconds" cdk/PKG/chip | sort
cdk/PKG/chip/bcm53101/bcm53101_a0_defs.h

$ grep -l -r "Specifies the aging time in seconds" cdk/PKG/chip | sort
cdk/PKG/chip/bcm53010/bcm53010_a0_defs.h
cdk/PKG/chip/bcm53020/bcm53020_a0_defs.h
cdk/PKG/chip/bcm53084/bcm53084_a0_defs.h
cdk/PKG/chip/bcm53115/bcm53115_a0_defs.h
cdk/PKG/chip/bcm53118/bcm53118_a0_defs.h
cdk/PKG/chip/bcm53125/bcm53125_a0_defs.h
cdk/PKG/chip/bcm53128/bcm53128_a0_defs.h
cdk/PKG/chip/bcm53134/bcm53134_a0_defs.h
cdk/PKG/chip/bcm53242/bcm53242_a0_defs.h
cdk/PKG/chip/bcm53262/bcm53262_a0_defs.h
cdk/PKG/chip/bcm53280/bcm53280_a0_defs.h
cdk/PKG/chip/bcm53280/bcm53280_b0_defs.h
cdk/PKG/chip/bcm53600/bcm53600_a0_defs.h
cdk/PKG/chip/bcm89500/bcm89500_a0_defs.h

[1] https://github.com/Broadcom/OpenMDK/blob/a5d3fc9b12af3eeb68f2ca0ce7ec4056cd14d6c2/cdk/PKG/chip/bcm53101/bcm53101_a0_defs.h#L28966

Fixes: e39d14a ("net: dsa: b53: implement setting ageing time")
Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://patch.msgid.link/20250905124507.59186-1-jonas.gorski@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: KanjiMonster

drivers/net/dsa/b53/b53_common.c

@@ -1273,9 +1273,15 @@ static int b53_setup(struct dsa_switch *ds)
 	 */
 	ds->untag_vlan_aware_bridge_pvid = true;
 
-	/* Ageing time is set in seconds */
-	ds->ageing_time_min = 1 * 1000;
-	ds->ageing_time_max = AGE_TIME_MAX * 1000;
+	if (dev->chip_id == BCM53101_DEVICE_ID) {
+		/* BCM53101 uses 0.5 second increments */
+		ds->ageing_time_min = 1 * 500;
+		ds->ageing_time_max = AGE_TIME_MAX * 500;
+	} else {
+		/* Everything else uses 1 second increments */
+		ds->ageing_time_min = 1 * 1000;
+		ds->ageing_time_max = AGE_TIME_MAX * 1000;
+	}
 
 	ret = b53_reset_switch(dev);
 	if (ret) {
@@ -2559,7 +2565,10 @@ int b53_set_ageing_time(struct dsa_switch *ds, unsigned int msecs)
 	else
 		reg = B53_AGING_TIME_CONTROL;
 
-	atc = DIV_ROUND_CLOSEST(msecs, 1000);
+	if (dev->chip_id == BCM53101_DEVICE_ID)
+		atc = DIV_ROUND_CLOSEST(msecs, 500);
+	else
+		atc = DIV_ROUND_CLOSEST(msecs, 1000);
 
 	if (!is5325(dev) && !is5365(dev))
 		atc |= AGE_CHANGE;