[PATCH net-next 2/2] net: dsa: microchip: add KSZ8 change_tag_protocol support

[vtpieter@gmail.com]

From: Pieter Van Trappen <pieter.van.trappen@cern.ch>

Add support for changing the KSZ8 switches tag protocol. In fact
these devices can only enable or disable the tail tag, so there's
really only three supported protocols:
- DSA_TAG_PROTO_KSZ8795 for KSZ87xx
- DSA_TAG_PROTO_KSZ9893 for KSZ88x3
- DSA_TAG_PROTO_NONE

When disabled, this can be used as a workaround for the 'Common
pitfalls using DSA setups' [1] to use the conduit network interface as
a regular one, admittedly forgoing most DSA functionality and using
the device as an unmanaged switch whilst allowing control
operations (ethtool, PHY management, WoL). Implementing the new
software-defined DSA tagging protocol tag_8021q [2] for these devices
seems overkill for this use case at the time being.

In addition, shorten certain dev->chip_id checks by using the existing
ksz_is_ksz87xx instead.

Link: https://www.kernel.org/doc/html/latest/networking/dsa/dsa.html [1]
Link: https://lpc.events/event/11/contributions/949/attachments/823/1555/paper.pdf [2]
Signed-off-by: Pieter Van Trappen <pieter.van.trappen@cern.ch>
---
 drivers/net/dsa/microchip/ksz8.h       |  2 ++
 drivers/net/dsa/microchip/ksz8795.c    | 27 ++++++++++++++++++++++++++
 drivers/net/dsa/microchip/ksz_common.c | 24 +++++++++++++++++------
 drivers/net/dsa/microchip/ksz_common.h |  2 ++
 4 files changed, 49 insertions(+), 6 deletions(-)

diff --git a/drivers/net/dsa/microchip/ksz8.h b/drivers/net/dsa/microchip/ksz8.h
index e1c79ff97123..14c7912b854e 100644
--- a/drivers/net/dsa/microchip/ksz8.h
+++ b/drivers/net/dsa/microchip/ksz8.h
@@ -57,6 +57,8 @@ int ksz8_change_mtu(struct ksz_device *dev, int port, int mtu);
 int ksz8_pme_write8(struct ksz_device *dev, u32 reg, u8 value);
 int ksz8_pme_pread8(struct ksz_device *dev, int port, int offset, u8 *data);
 int ksz8_pme_pwrite8(struct ksz_device *dev, int port, int offset, u8 data);
+int ksz8_change_tag_protocol(struct ksz_device *dev,
+			     enum dsa_tag_protocol proto);
 void ksz8_phylink_mac_link_up(struct phylink_config *config,
 			      struct phy_device *phydev, unsigned int mode,
 			      phy_interface_t interface, int speed, int duplex,
diff --git a/drivers/net/dsa/microchip/ksz8795.c b/drivers/net/dsa/microchip/ksz8795.c
index a01079297a8c..41d163e88f03 100644
--- a/drivers/net/dsa/microchip/ksz8795.c
+++ b/drivers/net/dsa/microchip/ksz8795.c
@@ -194,6 +194,33 @@ int ksz8_change_mtu(struct ksz_device *dev, int port, int mtu)
 	return -EOPNOTSUPP;
 }
 
+/**
+ * ksz8_change_tag_protocol - Change tag protocol
+ * @dev: The device structure.
+ * @proto: The requested protocol.
+ *
+ * This function allows changing the tag protocol. In fact the ksz8
+ * devices can only enable or disable the tail tag.
+ *
+ * Return: 0 on success, -EPROTONOSUPPORT in case protocol not supported.
+ */
+int ksz8_change_tag_protocol(struct ksz_device *dev,
+			     enum dsa_tag_protocol proto)
+{
+	const u32 *masks = dev->info->masks;
+	const u16 *regs = dev->info->regs;
+
+	if ((proto == DSA_TAG_PROTO_KSZ8795 && ksz_is_ksz87xx(dev)) ||
+	    (proto == DSA_TAG_PROTO_KSZ9893 && ksz_is_ksz88x3(dev)))
+		ksz_cfg(dev, regs[S_TAIL_TAG_CTRL], masks[SW_TAIL_TAG_ENABLE], true);
+	else if (proto == DSA_TAG_PROTO_NONE)
+		ksz_cfg(dev, regs[S_TAIL_TAG_CTRL], masks[SW_TAIL_TAG_ENABLE], false);
+	else
+		return -EPROTONOSUPPORT;
+
+	return 0;
+}
+
 static int ksz8_port_queue_split(struct ksz_device *dev, int port, int queues)
 {
 	u8 mask_4q, mask_2q;
diff --git a/drivers/net/dsa/microchip/ksz_common.c b/drivers/net/dsa/microchip/ksz_common.c
index cd3991792b69..e5194660ed99 100644
--- a/drivers/net/dsa/microchip/ksz_common.c
+++ b/drivers/net/dsa/microchip/ksz_common.c
@@ -310,6 +310,7 @@ static const struct ksz_dev_ops ksz88x3_dev_ops = {
 	.pme_write8 = ksz8_pme_write8,
 	.pme_pread8 = ksz8_pme_pread8,
 	.pme_pwrite8 = ksz8_pme_pwrite8,
+	.change_tag_protocol = ksz8_change_tag_protocol,
 };
 
 static const struct ksz_dev_ops ksz87xx_dev_ops = {
@@ -345,6 +346,7 @@ static const struct ksz_dev_ops ksz87xx_dev_ops = {
 	.pme_write8 = ksz8_pme_write8,
 	.pme_pread8 = ksz8_pme_pread8,
 	.pme_pwrite8 = ksz8_pme_pwrite8,
+	.change_tag_protocol = ksz8_change_tag_protocol,
 };
 
 static void ksz9477_phylink_mac_link_up(struct phylink_config *config,
@@ -2937,9 +2939,7 @@ static enum dsa_tag_protocol ksz_get_tag_protocol(struct dsa_switch *ds,
 	struct ksz_device *dev = ds->priv;
 	enum dsa_tag_protocol proto = DSA_TAG_PROTO_NONE;
 
-	if (dev->chip_id == KSZ8795_CHIP_ID ||
-	    dev->chip_id == KSZ8794_CHIP_ID ||
-	    dev->chip_id == KSZ8765_CHIP_ID)
+	if (ksz_is_ksz87xx(dev))
 		proto = DSA_TAG_PROTO_KSZ8795;
 
 	if (dev->chip_id == KSZ8830_CHIP_ID ||
@@ -2961,12 +2961,25 @@ static enum dsa_tag_protocol ksz_get_tag_protocol(struct dsa_switch *ds,
 	return proto;
 }
 
+static int ksz_change_tag_protocol(struct dsa_switch *ds,
+				   enum dsa_tag_protocol proto)
+{
+	struct ksz_device *dev = ds->priv;
+
+	if (dev->dev_ops->change_tag_protocol)
+		return dev->dev_ops->change_tag_protocol(dev, proto);
+	else
+		return -EPROTONOSUPPORT;
+}
+
 static int ksz_connect_tag_protocol(struct dsa_switch *ds,
 				    enum dsa_tag_protocol proto)
 {
 	struct ksz_tagger_data *tagger_data;
 
 	switch (proto) {
+	case DSA_TAG_PROTO_NONE:
+		return 0;
 	case DSA_TAG_PROTO_KSZ8795:
 		return 0;
 	case DSA_TAG_PROTO_KSZ9893:
@@ -4208,6 +4221,7 @@ static int ksz_hsr_leave(struct dsa_switch *ds, int port,
 
 static const struct dsa_switch_ops ksz_switch_ops = {
 	.get_tag_protocol	= ksz_get_tag_protocol,
+	.change_tag_protocol    = ksz_change_tag_protocol,
 	.connect_tag_protocol   = ksz_connect_tag_protocol,
 	.get_phy_flags		= ksz_get_phy_flags,
 	.setup			= ksz_setup,
@@ -4443,9 +4457,7 @@ static int ksz9477_drive_strength_write(struct ksz_device *dev,
 		dev_warn(dev->dev, "%s is not supported by this chip variant\n",
 			 props[KSZ_DRIVER_STRENGTH_IO].name);
 
-	if (dev->chip_id == KSZ8795_CHIP_ID ||
-	    dev->chip_id == KSZ8794_CHIP_ID ||
-	    dev->chip_id == KSZ8765_CHIP_ID)
+	if (ksz_is_ksz87xx(dev))
 		reg = KSZ8795_REG_SW_CTRL_20;
 	else
 		reg = KSZ9477_REG_SW_IO_STRENGTH;
diff --git a/drivers/net/dsa/microchip/ksz_common.h b/drivers/net/dsa/microchip/ksz_common.h
index 8094d90d6ca4..e1178063e6e4 100644
--- a/drivers/net/dsa/microchip/ksz_common.h
+++ b/drivers/net/dsa/microchip/ksz_common.h
@@ -363,6 +363,8 @@ struct ksz_dev_ops {
 			  u8 *data);
 	int (*pme_pwrite8)(struct ksz_device *dev, int port, int offset,
 			   u8 data);
+	int (*change_tag_protocol)(struct ksz_device *dev,
+				   enum dsa_tag_protocol proto);
 	void (*freeze_mib)(struct ksz_device *dev, int port, bool freeze);
 	void (*port_init_cnt)(struct ksz_device *dev, int port);
 	void (*phylink_mac_link_up)(struct ksz_device *dev, int port,
-- 
2.43.0