// 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);

/* 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);
	struct dsa_port *dp = &ds->ports[port];
	struct dsa_port *upstream_dp = &ds->ports[upstream];
	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++) {
		struct dsa_port *other_dp = &ds->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;

		if (enabled)
			err = dsa_port_vid_add(other_dp, rx_vid, flags);
		else
			err = dsa_port_vid_del(other_dp, rx_vid);
		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.
	 */
	if (enabled)
		err = dsa_port_vid_add(upstream_dp, rx_vid, 0);
	else
		err = dsa_port_vid_del(upstream_dp, rx_vid);
	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 */
	if (enabled)
		err = dsa_port_vid_add(dp, tx_vid, BRIDGE_VLAN_INFO_UNTAGGED);
	else
		err = dsa_port_vid_del(dp, tx_vid);
	if (err) {
		dev_err(ds->dev, "Failed to apply TX VID %d on port %d: %d\n",
			tx_vid, port, err);
		return err;
	}
	if (enabled)
		err = dsa_port_vid_add(upstream_dp, tx_vid, 0);
	else
		err = dsa_port_vid_del(upstream_dp, tx_vid);
	if (err) {
		dev_err(ds->dev, "Failed to apply TX VID %d on port %d: %d\n",
			tx_vid, upstream, err);
		return err;
	}

	return 0;
}
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);

/* In the DSA packet_type handler, skb->data points in the middle of the VLAN
 * tag, after tpid and before tci. This is because so far, ETH_HLEN
 * (DMAC, SMAC, EtherType) bytes were pulled.
 * There are 2 bytes of VLAN tag left in skb->data, and upper
 * layers expect the 'real' EtherType to be consumed as well.
 * Coincidentally, a VLAN header is also of the same size as
 * the number of bytes that need to be pulled.
 *
 * skb_mac_header                                      skb->data
 * |                                                       |
 * v                                                       v
 * |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
 * +-----------------------+-----------------------+-------+-------+-------+
 * |    Destination MAC    |      Source MAC       |  TPID |  TCI  | EType |
 * +-----------------------+-----------------------+-------+-------+-------+
 * ^                                               |               |
 * |<--VLAN_HLEN-->to                              <---VLAN_HLEN--->
 * from            |
 *       >>>>>>>   v
 *       >>>>>>>   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
 *       >>>>>>>   +-----------------------+-----------------------+-------+
 *       >>>>>>>   |    Destination MAC    |      Source MAC       | EType |
 *                 +-----------------------+-----------------------+-------+
 *                 ^                                                       ^
 * (now part of    |                                                       |
 *  skb->head)     skb_mac_header                                  skb->data
 */
struct sk_buff *dsa_8021q_remove_header(struct sk_buff *skb)
{
	u8 *from = skb_mac_header(skb);
	u8 *dest = from + VLAN_HLEN;

	memmove(dest, from, ETH_HLEN - VLAN_HLEN);
	skb_pull(skb, VLAN_HLEN);
	skb_push(skb, ETH_HLEN);
	skb_reset_mac_header(skb);
	skb_reset_mac_len(skb);
	skb_pull_rcsum(skb, ETH_HLEN);

	return skb;
}
EXPORT_SYMBOL_GPL(dsa_8021q_remove_header);

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);