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Message-Id: <20231209-rtl8366rb-mtu-fix-v1-2-df863e2b2b2a@linaro.org>
Date: Sat, 09 Dec 2023 23:37:35 +0100
From: Linus Walleij <linus.walleij@...aro.org>
To: Alvin Šipraga <alsi@...g-olufsen.dk>,
Andrew Lunn <andrew@...n.ch>, Florian Fainelli <f.fainelli@...il.com>,
Vladimir Oltean <olteanv@...il.com>,
"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, Linus Walleij <linus.walleij@...aro.org>
Subject: [PATCH net-next 2/2] net: dsa: realtek: Rewrite RTL8366RB MTU
handling
The MTU callbacks are in layer 1 size, so for example 1500
bytes is a normal setting. Cache this size, and only add
the layer 2 framing right before choosing the setting. On
the CPU port this will however include the DSA tag since
this is transmitted from the parent ethernet interface!
Add the layer 2 overhead such as ethernet and VLAN framing
and FCS before selecting the size in the register.
This will make the code easier to understand.
The rtl8366rb_max_mtu() callback returns a bogus MTU
just subtracting the CPU tag, which is the only thing
we should NOT subtract. Return the correct layer 1
max MTU after removing headers and checksum.
Signed-off-by: Linus Walleij <linus.walleij@...aro.org>
---
drivers/net/dsa/realtek/rtl8366rb.c | 48 +++++++++++++++++++++++--------------
1 file changed, 30 insertions(+), 18 deletions(-)
diff --git a/drivers/net/dsa/realtek/rtl8366rb.c b/drivers/net/dsa/realtek/rtl8366rb.c
index 887afd1392cb..e3b6a470ca67 100644
--- a/drivers/net/dsa/realtek/rtl8366rb.c
+++ b/drivers/net/dsa/realtek/rtl8366rb.c
@@ -15,6 +15,7 @@
#include <linux/bitops.h>
#include <linux/etherdevice.h>
#include <linux/if_bridge.h>
+#include <linux/if_vlan.h>
#include <linux/interrupt.h>
#include <linux/irqdomain.h>
#include <linux/irqchip/chained_irq.h>
@@ -929,15 +930,19 @@ static int rtl8366rb_setup(struct dsa_switch *ds)
if (ret)
return ret;
- /* Set maximum packet length to 1536 bytes */
+ /* Set default maximum packet length to 1536 bytes */
ret = regmap_update_bits(priv->map, RTL8366RB_SGCR,
RTL8366RB_SGCR_MAX_LENGTH_MASK,
RTL8366RB_SGCR_MAX_LENGTH_1536);
if (ret)
return ret;
- for (i = 0; i < RTL8366RB_NUM_PORTS; i++)
- /* layer 2 size, see rtl8366rb_change_mtu() */
- rb->max_mtu[i] = 1532;
+ for (i = 0; i < RTL8366RB_NUM_PORTS; i++) {
+ if (i == priv->cpu_port)
+ /* CPU port need to also accept the tag */
+ rb->max_mtu[i] = ETH_DATA_LEN + RTL8366RB_CPU_TAG_SIZE;
+ else
+ rb->max_mtu[i] = ETH_DATA_LEN;
+ }
/* Disable learning for all ports */
ret = regmap_write(priv->map, RTL8366RB_PORT_LEARNDIS_CTRL,
@@ -1442,24 +1447,29 @@ static int rtl8366rb_change_mtu(struct dsa_switch *ds, int port, int new_mtu)
/* Roof out the MTU for the entire switch to the greatest
* common denominator: the biggest set for any one port will
* be the biggest MTU for the switch.
- *
- * The first setting, 1522 bytes, is max IP packet 1500 bytes,
- * plus ethernet header, 1518 bytes, plus CPU tag, 4 bytes.
- * This function should consider the parameter an SDU, so the
- * MTU passed for this setting is 1518 bytes. The same logic
- * of subtracting the DSA tag of 4 bytes apply to the other
- * settings.
*/
- max_mtu = 1518;
+ max_mtu = ETH_DATA_LEN;
for (i = 0; i < RTL8366RB_NUM_PORTS; i++) {
if (rb->max_mtu[i] > max_mtu)
max_mtu = rb->max_mtu[i];
}
- if (max_mtu <= 1518)
+
+ /* Translate to layer 2 size.
+ * Add ethernet and (possible) VLAN headers, and checksum to the size.
+ * For ETH_DATA_LEN (1500 bytes) this will add up to 1522 bytes.
+ */
+ max_mtu += VLAN_ETH_HLEN;
+ max_mtu += ETH_FCS_LEN;
+
+ if (max_mtu <= 1522)
len = RTL8366RB_SGCR_MAX_LENGTH_1522;
- else if (max_mtu > 1518 && max_mtu <= 1532)
+ else if (max_mtu > 1522 && max_mtu <= 1536)
+ /* This will be the most common default if using VLAN and
+ * CPU tagging on a port as both VLAN and CPU tag will
+ * result in 1518 + 4 + 4 = 1526 bytes.
+ */
len = RTL8366RB_SGCR_MAX_LENGTH_1536;
- else if (max_mtu > 1532 && max_mtu <= 1548)
+ else if (max_mtu > 1536 && max_mtu <= 1552)
len = RTL8366RB_SGCR_MAX_LENGTH_1552;
else
len = RTL8366RB_SGCR_MAX_LENGTH_16000;
@@ -1471,10 +1481,12 @@ static int rtl8366rb_change_mtu(struct dsa_switch *ds, int port, int new_mtu)
static int rtl8366rb_max_mtu(struct dsa_switch *ds, int port)
{
- /* The max MTU is 16000 bytes, so we subtract the CPU tag
- * and the max presented to the system is 15996 bytes.
+ /* The max MTU is 16000 bytes, so we subtract the ethernet
+ * headers with VLAN and checksum and arrive at
+ * 16000 - 18 - 4 = 15978. This does not include the CPU tag
+ * since that is added to the requested MTU by the DSA framework.
*/
- return 15996;
+ return 16000 - VLAN_ETH_HLEN - ETH_FCS_LEN;
}
static int rtl8366rb_get_vlan_4k(struct realtek_priv *priv, u32 vid,
--
2.34.1
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