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net: dsa: realtek: Rewrite RTL8366RB MTU handling

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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@linaro.org>
Reviewed-by: Alvin Šipraga <alsi@bang-olufsen.dk>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Linus Walleij 2023-12-09 23:37:35 +01:00 committed by Paolo Abeni
parent 389119c842
commit d577ca429a
1 changed files with 30 additions and 18 deletions
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48
drivers/net/dsa/realtek/rtl8366rb.c
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@ -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,