From d577ca429af36a3aea38d53d11be56dff015dfc9 Mon Sep 17 00:00:00 2001 From: Linus Walleij Date: Sat, 9 Dec 2023 23:37:35 +0100 Subject: [PATCH] net: dsa: realtek: Rewrite RTL8366RB MTU handling MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Reviewed-by: Alvin Šipraga Reviewed-by: Florian Fainelli Signed-off-by: Paolo Abeni --- 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 #include #include +#include #include #include #include @@ -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,