linux-brain/net/dsa/tag_8021q.c

// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2019, Vladimir Oltean <olteanv@gmail.com>
 *
 * This module is not a complete tagger implementation. It only provides
 * primitives for taggers that rely on 802.1Q VLAN tags to use. The
 * dsa_8021q_netdev_ops is registered for API compliance and not used
 * directly by callers.
 */
#include <linux/if_bridge.h>
#include <linux/if_vlan.h>

#include "dsa_priv.h"

/* Binary structure of the fake 12-bit VID field (when the TPID is
 * ETH_P_DSA_8021Q):
 *
 * | 11  | 10  |  9  |  8  |  7  |  6  |  5  |  4  |  3  |  2  |  1  |  0  |
 * +-----------+-----+-----------------+-----------+-----------------------+
 * |    DIR    | RSV |    SWITCH_ID    |    RSV    |          PORT         |
 * +-----------+-----+-----------------+-----------+-----------------------+
 *
 * DIR - VID[11:10]:
 *	Direction flags.
 *	* 1 (0b01) for RX VLAN,
 *	* 2 (0b10) for TX VLAN.
 *	These values make the special VIDs of 0, 1 and 4095 to be left
 *	unused by this coding scheme.
 *
 * RSV - VID[9]:
 *	To be used for further expansion of SWITCH_ID or for other purposes.
 *	Must be transmitted as zero and ignored on receive.
 *
 * SWITCH_ID - VID[8:6]:
 *	Index of switch within DSA tree. Must be between 0 and
 *	DSA_MAX_SWITCHES - 1.
 *
 * RSV - VID[5:4]:
 *	To be used for further expansion of PORT or for other purposes.
 *	Must be transmitted as zero and ignored on receive.
 *
 * PORT - VID[3:0]:
 *	Index of switch port. Must be between 0 and DSA_MAX_PORTS - 1.
 */

#define DSA_8021Q_DIR_SHIFT		10
#define DSA_8021Q_DIR_MASK		GENMASK(11, 10)
#define DSA_8021Q_DIR(x)		(((x) << DSA_8021Q_DIR_SHIFT) & \
						 DSA_8021Q_DIR_MASK)
#define DSA_8021Q_DIR_RX		DSA_8021Q_DIR(1)
#define DSA_8021Q_DIR_TX		DSA_8021Q_DIR(2)

#define DSA_8021Q_SWITCH_ID_SHIFT	6
#define DSA_8021Q_SWITCH_ID_MASK	GENMASK(8, 6)
#define DSA_8021Q_SWITCH_ID(x)		(((x) << DSA_8021Q_SWITCH_ID_SHIFT) & \
						 DSA_8021Q_SWITCH_ID_MASK)

#define DSA_8021Q_PORT_SHIFT		0
#define DSA_8021Q_PORT_MASK		GENMASK(3, 0)
#define DSA_8021Q_PORT(x)		(((x) << DSA_8021Q_PORT_SHIFT) & \
						 DSA_8021Q_PORT_MASK)

/* Returns the VID to be inserted into the frame from xmit for switch steering
 * instructions on egress. Encodes switch ID and port ID.
 */
u16 dsa_8021q_tx_vid(struct dsa_switch *ds, int port)
{
	return DSA_8021Q_DIR_TX | DSA_8021Q_SWITCH_ID(ds->index) |
	       DSA_8021Q_PORT(port);
}
EXPORT_SYMBOL_GPL(dsa_8021q_tx_vid);

/* Returns the VID that will be installed as pvid for this switch port, sent as
 * tagged egress towards the CPU port and decoded by the rcv function.
 */
u16 dsa_8021q_rx_vid(struct dsa_switch *ds, int port)
{
	return DSA_8021Q_DIR_RX | DSA_8021Q_SWITCH_ID(ds->index) |
	       DSA_8021Q_PORT(port);
}
EXPORT_SYMBOL_GPL(dsa_8021q_rx_vid);

/* Returns the decoded switch ID from the RX VID. */
int dsa_8021q_rx_switch_id(u16 vid)
{
	return (vid & DSA_8021Q_SWITCH_ID_MASK) >> DSA_8021Q_SWITCH_ID_SHIFT;
}
EXPORT_SYMBOL_GPL(dsa_8021q_rx_switch_id);

/* Returns the decoded port ID from the RX VID. */
int dsa_8021q_rx_source_port(u16 vid)
{
	return (vid & DSA_8021Q_PORT_MASK) >> DSA_8021Q_PORT_SHIFT;
}
EXPORT_SYMBOL_GPL(dsa_8021q_rx_source_port);

static int dsa_8021q_restore_pvid(struct dsa_switch *ds, int port)
{
	struct bridge_vlan_info vinfo;
	struct net_device *slave;
	u16 pvid;
	int err;

	if (!dsa_is_user_port(ds, port))
		return 0;

	slave = ds->ports[port].slave;

	err = br_vlan_get_pvid(slave, &pvid);
	if (!pvid || err < 0)
		/* There is no pvid on the bridge for this port, which is
		 * perfectly valid. Nothing to restore, bye-bye!
		 */
		return 0;

	err = br_vlan_get_info(slave, pvid, &vinfo);
	if (err < 0) {
		dev_err(ds->dev, "Couldn't determine PVID attributes\n");
		return err;
	}

	return dsa_port_vid_add(&ds->ports[port], pvid, vinfo.flags);
}

/* If @enabled is true, installs @vid with @flags into the switch port's HW
 * filter.
 * If @enabled is false, deletes @vid (ignores @flags) from the port. Had the
 * user explicitly configured this @vid through the bridge core, then the @vid
 * is installed again, but this time with the flags from the bridge layer.
 */
static int dsa_8021q_vid_apply(struct dsa_switch *ds, int port, u16 vid,
			       u16 flags, bool enabled)
{
	struct dsa_port *dp = &ds->ports[port];
	struct bridge_vlan_info vinfo;
	int err;

	if (enabled)
		return dsa_port_vid_add(dp, vid, flags);

	err = dsa_port_vid_del(dp, vid);
	if (err < 0)
		return err;

	/* Nothing to restore from the bridge for a non-user port.
	 * The CPU port VLANs are restored implicitly with the user ports,
	 * similar to how the bridge does in dsa_slave_vlan_add and
	 * dsa_slave_vlan_del.
	 */
	if (!dsa_is_user_port(ds, port))
		return 0;

	err = br_vlan_get_info(dp->slave, vid, &vinfo);
	/* Couldn't determine bridge attributes for this vid,
	 * it means the bridge had not configured it.
	 */
	if (err < 0)
		return 0;

	/* Restore the VID from the bridge */
	err = dsa_port_vid_add(dp, vid, vinfo.flags);
	if (err < 0)
		return err;

	vinfo.flags &= ~BRIDGE_VLAN_INFO_PVID;

	return dsa_port_vid_add(dp->cpu_dp, vid, vinfo.flags);
}

/* RX VLAN tagging (left) and TX VLAN tagging (right) setup shown for a single
 * front-panel switch port (here swp0).
 *
 * Port identification through VLAN (802.1Q) tags has different requirements
 * for it to work effectively:
 *  - On RX (ingress from network): each front-panel port must have a pvid
 *    that uniquely identifies it, and the egress of this pvid must be tagged
 *    towards the CPU port, so that software can recover the source port based
 *    on the VID in the frame. But this would only work for standalone ports;
 *    if bridged, this VLAN setup would break autonomous forwarding and would
 *    force all switched traffic to pass through the CPU. So we must also make
 *    the other front-panel ports members of this VID we're adding, albeit
 *    we're not making it their PVID (they'll still have their own).
 *    By the way - just because we're installing the same VID in multiple
 *    switch ports doesn't mean that they'll start to talk to one another, even
 *    while not bridged: the final forwarding decision is still an AND between
 *    the L2 forwarding information (which is limiting forwarding in this case)
 *    and the VLAN-based restrictions (of which there are none in this case,
 *    since all ports are members).
 *  - On TX (ingress from CPU and towards network) we are faced with a problem.
 *    If we were to tag traffic (from within DSA) with the port's pvid, all
 *    would be well, assuming the switch ports were standalone. Frames would
 *    have no choice but to be directed towards the correct front-panel port.
 *    But because we also want the RX VLAN to not break bridging, then
 *    inevitably that means that we have to give them a choice (of what
 *    front-panel port to go out on), and therefore we cannot steer traffic
 *    based on the RX VID. So what we do is simply install one more VID on the
 *    front-panel and CPU ports, and profit off of the fact that steering will
 *    work just by virtue of the fact that there is only one other port that's
 *    a member of the VID we're tagging the traffic with - the desired one.
 *
 * So at the end, each front-panel port will have one RX VID (also the PVID),
 * the RX VID of all other front-panel ports, and one TX VID. Whereas the CPU
 * port will have the RX and TX VIDs of all front-panel ports, and on top of
 * that, is also tagged-input and tagged-output (VLAN trunk).
 *
 *               CPU port                               CPU port
 * +-------------+-----+-------------+    +-------------+-----+-------------+
 * |  RX VID     |     |             |    |  TX VID     |     |             |
 * |  of swp0    |     |             |    |  of swp0    |     |             |
 * |             +-----+             |    |             +-----+             |
 * |                ^ T              |    |                | Tagged         |
 * |                |                |    |                | ingress        |
 * |    +-------+---+---+-------+    |    |    +-----------+                |
 * |    |       |       |       |    |    |    | Untagged                   |
 * |    |     U v     U v     U v    |    |    v egress                     |
 * | +-----+ +-----+ +-----+ +-----+ |    | +-----+ +-----+ +-----+ +-----+ |
 * | |     | |     | |     | |     | |    | |     | |     | |     | |     | |
 * | |PVID | |     | |     | |     | |    | |     | |     | |     | |     | |
 * +-+-----+-+-----+-+-----+-+-----+-+    +-+-----+-+-----+-+-----+-+-----+-+
 *   swp0    swp1    swp2    swp3           swp0    swp1    swp2    swp3
 */
int dsa_port_setup_8021q_tagging(struct dsa_switch *ds, int port, bool enabled)
{
	int upstream = dsa_upstream_port(ds, port);
	u16 rx_vid = dsa_8021q_rx_vid(ds, port);
	u16 tx_vid = dsa_8021q_tx_vid(ds, port);
	int i, err;

	/* The CPU port is implicitly configured by
	 * configuring the front-panel ports
	 */
	if (!dsa_is_user_port(ds, port))
		return 0;

	/* Add this user port's RX VID to the membership list of all others
	 * (including itself). This is so that bridging will not be hindered.
	 * L2 forwarding rules still take precedence when there are no VLAN
	 * restrictions, so there are no concerns about leaking traffic.
	 */
	for (i = 0; i < ds->num_ports; i++) {
		u16 flags;

		if (i == upstream)
			continue;
		else if (i == port)
			/* The RX VID is pvid on this port */
			flags = BRIDGE_VLAN_INFO_UNTAGGED |
				BRIDGE_VLAN_INFO_PVID;
		else
			/* The RX VID is a regular VLAN on all others */
			flags = BRIDGE_VLAN_INFO_UNTAGGED;

		err = dsa_8021q_vid_apply(ds, i, rx_vid, flags, enabled);
		if (err) {
			dev_err(ds->dev, "Failed to apply RX VID %d to port %d: %d\n",
				rx_vid, port, err);
			return err;
		}
	}

	/* CPU port needs to see this port's RX VID
	 * as tagged egress.
	 */
	err = dsa_8021q_vid_apply(ds, upstream, rx_vid, 0, enabled);
	if (err) {
		dev_err(ds->dev, "Failed to apply RX VID %d to port %d: %d\n",
			rx_vid, port, err);
		return err;
	}

	/* Finally apply the TX VID on this port and on the CPU port */
	err = dsa_8021q_vid_apply(ds, port, tx_vid, BRIDGE_VLAN_INFO_UNTAGGED,
				  enabled);
	if (err) {
		dev_err(ds->dev, "Failed to apply TX VID %d on port %d: %d\n",
			tx_vid, port, err);
		return err;
	}
	err = dsa_8021q_vid_apply(ds, upstream, tx_vid, 0, enabled);
	if (err) {
		dev_err(ds->dev, "Failed to apply TX VID %d on port %d: %d\n",
			tx_vid, upstream, err);
		return err;
	}

	if (!enabled)
		err = dsa_8021q_restore_pvid(ds, port);

	return err;
}
EXPORT_SYMBOL_GPL(dsa_port_setup_8021q_tagging);

struct sk_buff *dsa_8021q_xmit(struct sk_buff *skb, struct net_device *netdev,
			       u16 tpid, u16 tci)
{
	/* skb->data points at skb_mac_header, which
	 * is fine for vlan_insert_tag.
	 */
	return vlan_insert_tag(skb, htons(tpid), tci);
}
EXPORT_SYMBOL_GPL(dsa_8021q_xmit);

static const struct dsa_device_ops dsa_8021q_netdev_ops = {
	.name		= "8021q",
	.proto		= DSA_TAG_PROTO_8021Q,
	.overhead	= VLAN_HLEN,
};

MODULE_LICENSE("GPL v2");
MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_8021Q);

module_dsa_tag_driver(dsa_8021q_netdev_ops);