[PATCH net v7 0/3] Handle new Microchip KSZ 9897 Errata

[PATCH net v7 0/3] Handle new Microchip KSZ 9897 Errata

[Enguerrand de Ribaucourt]

These patches implement some suggested workarounds from the Microchip KSZ 9897
Errata [1].

[1] https://ww1.microchip.com/downloads/aemDocuments/documents/UNG/ProductDocuments/Errata/KSZ9897R-Errata-DS80000758.pdf

---
v7:
 - use dev_crit_once instead of dev_crit_ratelimited
 - add a comment to help users understand the consequences of half-duplex errors
v6: https://lore.kernel.org/netdev/20240614094642.122464-1-enguerrand.de-ribaucourt@savoirfairelinux.com/
 - remove KSZ9897 phy_id workaround (was a configuration issue)
 - use macros for checking link down in monitoring function
 - check if VLAN is enabled before monitoring resources
v5: https://lore.kernel.org/all/20240604092304.314636-1-enguerrand.de-ribaucourt@savoirfairelinux.com/
 - use macros for bitfields
 - rewrap comments
 - check ksz_pread* return values
 - fix spelling mistakes
 - remove KSZ9477 suspend/resume deletion patch
v4: https://lore.kernel.org/all/20240531142430.678198-1-enguerrand.de-ribaucourt@savoirfairelinux.com/
 - Rebase on net/main
 - Add Fixes: tags to the patches
 - reverse x-mas tree order
 - use pseudo phy_id instead of match_phy_device
v3: https://lore.kernel.org/all/20240530102436.226189-1-enguerrand.de-ribaucourt@savoirfairelinux.com/

[PATCH net v7 1/3] net: phy: micrel: add Microchip KSZ 9477 to the device table

[Enguerrand de Ribaucourt]

PHY_ID_KSZ9477 was supported but not added to the device table passed to
MODULE_DEVICE_TABLE.

Fixes: fc3973a1fa09 ("phy: micrel: add Microchip KSZ 9477 Switch PHY support")
Signed-off-by: Enguerrand de Ribaucourt <enguerrand.de-ribaucourt@savoirfairelinux.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
---
v4:
 - rebase on net/main
 - add Fixes tag
v3: https://lore.kernel.org/all/20240530102436.226189-4-enguerrand.de-ribaucourt@savoirfairelinux.com/
---
 drivers/net/phy/micrel.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/phy/micrel.c b/drivers/net/phy/micrel.c
index 5aada7cf3da7..ebafedde0ab7 100644
--- a/drivers/net/phy/micrel.c
+++ b/drivers/net/phy/micrel.c
@@ -5607,6 +5607,7 @@ static struct mdio_device_id __maybe_unused micrel_tbl[] = {
 	{ PHY_ID_KSZ8081, MICREL_PHY_ID_MASK },
 	{ PHY_ID_KSZ8873MLL, MICREL_PHY_ID_MASK },
 	{ PHY_ID_KSZ886X, MICREL_PHY_ID_MASK },
+	{ PHY_ID_KSZ9477, MICREL_PHY_ID_MASK },
 	{ PHY_ID_LAN8814, MICREL_PHY_ID_MASK },
 	{ PHY_ID_LAN8804, MICREL_PHY_ID_MASK },
 	{ PHY_ID_LAN8841, MICREL_PHY_ID_MASK },
-- 
2.34.1

[PATCH net v7 2/3] net: dsa: microchip: use collision based back pressure mode

[Enguerrand de Ribaucourt]

Errata DS80000758 states that carrier sense back pressure mode can cause
link down issues in 100BASE-TX half duplex mode. The datasheet also
recommends to always use the collision based back pressure mode.

Fixes: b987e98e50ab ("dsa: add DSA switch driver for Microchip KSZ9477")
Signed-off-by: Enguerrand de Ribaucourt <enguerrand.de-ribaucourt@savoirfairelinux.com>
Reviewed-by: Woojung Huh <Woojung.huh@microchip.com>
Acked-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
---
v5:
 - define SW_BACK_PRESSURE_COLLISION
v4: https://lore.kernel.org/all/20240531142430.678198-5-enguerrand.de-ribaucourt@savoirfairelinux.com/
 - rebase on net/main
 - add Fixes tag
v3: https://lore.kernel.org/all/20240530102436.226189-5-enguerrand.de-ribaucourt@savoirfairelinux.com/
---
 drivers/net/dsa/microchip/ksz9477.c     | 4 ++++
 drivers/net/dsa/microchip/ksz9477_reg.h | 1 +
 2 files changed, 5 insertions(+)

diff --git a/drivers/net/dsa/microchip/ksz9477.c b/drivers/net/dsa/microchip/ksz9477.c
index f8ad7833f5d9..c2878dd0ad7e 100644
--- a/drivers/net/dsa/microchip/ksz9477.c
+++ b/drivers/net/dsa/microchip/ksz9477.c
@@ -1299,6 +1299,10 @@ int ksz9477_setup(struct dsa_switch *ds)
 	/* Enable REG_SW_MTU__2 reg by setting SW_JUMBO_PACKET */
 	ksz_cfg(dev, REG_SW_MAC_CTRL_1, SW_JUMBO_PACKET, true);
 
+	/* Use collision based back pressure mode. */
+	ksz_cfg(dev, REG_SW_MAC_CTRL_1, SW_BACK_PRESSURE,
+		SW_BACK_PRESSURE_COLLISION);
+
 	/* Now we can configure default MTU value */
 	ret = regmap_update_bits(ksz_regmap_16(dev), REG_SW_MTU__2, REG_SW_MTU_MASK,
 				 VLAN_ETH_FRAME_LEN + ETH_FCS_LEN);
diff --git a/drivers/net/dsa/microchip/ksz9477_reg.h b/drivers/net/dsa/microchip/ksz9477_reg.h
index f3a205ee483f..fb124be8edd3 100644
--- a/drivers/net/dsa/microchip/ksz9477_reg.h
+++ b/drivers/net/dsa/microchip/ksz9477_reg.h
@@ -247,6 +247,7 @@
 #define REG_SW_MAC_CTRL_1		0x0331
 
 #define SW_BACK_PRESSURE		BIT(5)
+#define SW_BACK_PRESSURE_COLLISION	0
 #define FAIR_FLOW_CTRL			BIT(4)
 #define NO_EXC_COLLISION_DROP		BIT(3)
 #define SW_JUMBO_PACKET			BIT(2)
-- 
2.34.1

[PATCH net v7 3/3] net: dsa: microchip: monitor potential faults in half-duplex mode

[Enguerrand de Ribaucourt]

The errata DS80000754 recommends monitoring potential faults in
half-duplex mode for the KSZ9477 family.

half-duplex is not very common so I just added a critical message
when the fault conditions are detected. The switch can be expected
to be unable to communicate anymore in these states and a software
reset of the switch would be required which I did not implement.

Fixes: b987e98e50ab ("dsa: add DSA switch driver for Microchip KSZ9477")
Signed-off-by: Enguerrand de Ribaucourt <enguerrand.de-ribaucourt@savoirfairelinux.com>
---
v7:
 - use dev_crit_once instead of dev_crit_ratelimited
   The condition will remain true forever and the routine called every
   5 seconds. There's no need to repeat the message.
 - add explanations in the comment above the warning to help users
   anticipate the consequences of the fault.
v6: https://lore.kernel.org/netdev/20240614094642.122464-4-enguerrand.de-ribaucourt@savoirfairelinux.com/
 - use macros for PORT_INTF_SPEED_MASK check
 - add VLAN condition before checking the resources
v5: https://lore.kernel.org/all/20240604092304.314636-5-enguerrand.de-ribaucourt@savoirfairelinux.com/
 - use macros for bitmasks
 - check for return values on ksz_pread*
v4: https://lore.kernel.org/all/20240531142430.678198-6-enguerrand.de-ribaucourt@savoirfairelinux.com/
 - rebase on net/main
 - add Fixes tag
 - reverse x-mas tree
v3: https://lore.kernel.org/all/20240530102436.226189-6-enguerrand.de-ribaucourt@savoirfairelinux.com/
---
 drivers/net/dsa/microchip/ksz9477.c     | 51 +++++++++++++++++++++++++
 drivers/net/dsa/microchip/ksz9477.h     |  2 +
 drivers/net/dsa/microchip/ksz9477_reg.h | 10 ++++-
 drivers/net/dsa/microchip/ksz_common.c  | 11 ++++++
 drivers/net/dsa/microchip/ksz_common.h  |  1 +
 5 files changed, 73 insertions(+), 2 deletions(-)

diff --git a/drivers/net/dsa/microchip/ksz9477.c b/drivers/net/dsa/microchip/ksz9477.c
index c2878dd0ad7e..6924b3818357 100644
--- a/drivers/net/dsa/microchip/ksz9477.c
+++ b/drivers/net/dsa/microchip/ksz9477.c
@@ -429,6 +429,57 @@ void ksz9477_freeze_mib(struct ksz_device *dev, int port, bool freeze)
 	mutex_unlock(&p->mib.cnt_mutex);
 }
 
+int ksz9477_errata_monitor(struct ksz_device *dev, int port,
+			   u64 tx_late_col)
+{
+	u32 pmavbc;
+	u8 status;
+	u16 pqm;
+	int ret;
+
+	ret = ksz_pread8(dev, port, REG_PORT_STATUS_0, &status);
+	if (ret)
+		return ret;
+	if (!(FIELD_GET(PORT_INTF_SPEED_MASK, status) == PORT_INTF_SPEED_NONE) &&
+	    !(status & PORT_INTF_FULL_DUPLEX)) {
+		/* Errata DS80000754 recommends monitoring potential faults in
+		 * half-duplex mode. The switch might not be able to communicate anymore
+		 * in these states.
+		 * If you see this message, please read the errata-sheet for more information:
+		 * https://ww1.microchip.com/downloads/aemDocuments/documents/UNG/ProductDocuments/Errata/KSZ9477S-Errata-DS80000754.pdf
+		 * To workaround this issue, half-duplex mode should be avoided.
+		 * A software reset could be implemented to recover from this state.
+		 */
+		dev_warn_once(dev->dev,
+			      "Half-duplex detected on port %d, transmission halt may occur\n",
+			      port);
+		if (tx_late_col != 0) {
+			/* Transmission halt with late collisions */
+			dev_crit_once(dev->dev,
+				      "TX late collisions detected, transmission may be halted on port %d\n",
+				      port);
+		}
+		ret = ksz_read8(dev, REG_SW_LUE_CTRL_0, &status);
+		if (ret)
+			return ret;
+		if (status & SW_VLAN_ENABLE) {
+			ret = ksz_pread16(dev, port, REG_PORT_QM_TX_CNT_0__4, &pqm);
+			if (ret)
+				return ret;
+			ret = ksz_read32(dev, REG_PMAVBC, &pmavbc);
+			if (ret)
+				return ret;
+			if ((FIELD_GET(PMAVBC_MASK, pmavbc) <= PMAVBC_MIN) ||
+			    (FIELD_GET(PORT_QM_TX_CNT_M, pqm) >= PORT_QM_TX_CNT_MAX)) {
+				/* Transmission halt with Half-Duplex and VLAN */
+				dev_crit_once(dev->dev,
+					      "resources out of limits, transmission may be halted\n");
+			}
+		}
+	}
+	return ret;
+}
+
 void ksz9477_port_init_cnt(struct ksz_device *dev, int port)
 {
 	struct ksz_port_mib *mib = &dev->ports[port].mib;
diff --git a/drivers/net/dsa/microchip/ksz9477.h b/drivers/net/dsa/microchip/ksz9477.h
index ce1e656b800b..239a281da10b 100644
--- a/drivers/net/dsa/microchip/ksz9477.h
+++ b/drivers/net/dsa/microchip/ksz9477.h
@@ -36,6 +36,8 @@ int ksz9477_port_mirror_add(struct ksz_device *dev, int port,
 			    bool ingress, struct netlink_ext_ack *extack);
 void ksz9477_port_mirror_del(struct ksz_device *dev, int port,
 			     struct dsa_mall_mirror_tc_entry *mirror);
+int ksz9477_errata_monitor(struct ksz_device *dev, int port,
+			   u64 tx_late_col);
 void ksz9477_get_caps(struct ksz_device *dev, int port,
 		      struct phylink_config *config);
 int ksz9477_fdb_dump(struct ksz_device *dev, int port,
diff --git a/drivers/net/dsa/microchip/ksz9477_reg.h b/drivers/net/dsa/microchip/ksz9477_reg.h
index fb124be8edd3..d5354c600ea1 100644
--- a/drivers/net/dsa/microchip/ksz9477_reg.h
+++ b/drivers/net/dsa/microchip/ksz9477_reg.h
@@ -843,8 +843,8 @@
 
 #define REG_PORT_STATUS_0		0x0030
 
-#define PORT_INTF_SPEED_M		0x3
-#define PORT_INTF_SPEED_S		3
+#define PORT_INTF_SPEED_MASK		GENMASK(4, 3)
+#define PORT_INTF_SPEED_NONE		GENMASK(1, 0)
 #define PORT_INTF_FULL_DUPLEX		BIT(2)
 #define PORT_TX_FLOW_CTRL		BIT(1)
 #define PORT_RX_FLOW_CTRL		BIT(0)
@@ -1168,6 +1168,11 @@
 #define PORT_RMII_CLK_SEL		BIT(7)
 #define PORT_MII_SEL_EDGE		BIT(5)
 
+#define REG_PMAVBC			0x03AC
+
+#define PMAVBC_MASK			GENMASK(26, 16)
+#define PMAVBC_MIN			0x580
+
 /* 4 - MAC */
 #define REG_PORT_MAC_CTRL_0		0x0400
 
@@ -1495,6 +1500,7 @@
 
 #define PORT_QM_TX_CNT_USED_S		0
 #define PORT_QM_TX_CNT_M		(BIT(11) - 1)
+#define PORT_QM_TX_CNT_MAX		0x200
 
 #define REG_PORT_QM_TX_CNT_1__4		0x0A14
 
diff --git a/drivers/net/dsa/microchip/ksz_common.c b/drivers/net/dsa/microchip/ksz_common.c
index 2818e24e2a51..0433109b42e5 100644
--- a/drivers/net/dsa/microchip/ksz_common.c
+++ b/drivers/net/dsa/microchip/ksz_common.c
@@ -1382,6 +1382,7 @@ const struct ksz_chip_data ksz_switch_chips[] = {
 		.tc_cbs_supported = true,
 		.ops = &ksz9477_dev_ops,
 		.phylink_mac_ops = &ksz9477_phylink_mac_ops,
+		.phy_errata_9477 = true,
 		.mib_names = ksz9477_mib_names,
 		.mib_cnt = ARRAY_SIZE(ksz9477_mib_names),
 		.reg_mib_cnt = MIB_COUNTER_NUM,
@@ -1416,6 +1417,7 @@ const struct ksz_chip_data ksz_switch_chips[] = {
 		.num_ipms = 8,
 		.ops = &ksz9477_dev_ops,
 		.phylink_mac_ops = &ksz9477_phylink_mac_ops,
+		.phy_errata_9477 = true,
 		.mib_names = ksz9477_mib_names,
 		.mib_cnt = ARRAY_SIZE(ksz9477_mib_names),
 		.reg_mib_cnt = MIB_COUNTER_NUM,
@@ -1450,6 +1452,7 @@ const struct ksz_chip_data ksz_switch_chips[] = {
 		.num_ipms = 8,
 		.ops = &ksz9477_dev_ops,
 		.phylink_mac_ops = &ksz9477_phylink_mac_ops,
+		.phy_errata_9477 = true,
 		.mib_names = ksz9477_mib_names,
 		.mib_cnt = ARRAY_SIZE(ksz9477_mib_names),
 		.reg_mib_cnt = MIB_COUNTER_NUM,
@@ -1540,6 +1543,7 @@ const struct ksz_chip_data ksz_switch_chips[] = {
 		.tc_cbs_supported = true,
 		.ops = &ksz9477_dev_ops,
 		.phylink_mac_ops = &ksz9477_phylink_mac_ops,
+		.phy_errata_9477 = true,
 		.mib_names = ksz9477_mib_names,
 		.mib_cnt = ARRAY_SIZE(ksz9477_mib_names),
 		.reg_mib_cnt = MIB_COUNTER_NUM,
@@ -1820,6 +1824,7 @@ void ksz_r_mib_stats64(struct ksz_device *dev, int port)
 	struct rtnl_link_stats64 *stats;
 	struct ksz_stats_raw *raw;
 	struct ksz_port_mib *mib;
+	int ret;
 
 	mib = &dev->ports[port].mib;
 	stats = &mib->stats64;
@@ -1861,6 +1866,12 @@ void ksz_r_mib_stats64(struct ksz_device *dev, int port)
 	pstats->rx_pause_frames = raw->rx_pause;
 
 	spin_unlock(&mib->stats64_lock);
+
+	if (dev->info->phy_errata_9477) {
+		ret = ksz9477_errata_monitor(dev, port, raw->tx_late_col);
+		if (ret)
+			dev_err(dev->dev, "Failed to monitor transmission halt\n");
+	}
 }
 
 void ksz88xx_r_mib_stats64(struct ksz_device *dev, int port)
diff --git a/drivers/net/dsa/microchip/ksz_common.h b/drivers/net/dsa/microchip/ksz_common.h
index c784fd23a993..ee7db46e469d 100644
--- a/drivers/net/dsa/microchip/ksz_common.h
+++ b/drivers/net/dsa/microchip/ksz_common.h
@@ -66,6 +66,7 @@ struct ksz_chip_data {
 	bool tc_cbs_supported;
 	const struct ksz_dev_ops *ops;
 	const struct phylink_mac_ops *phylink_mac_ops;
+	bool phy_errata_9477;
 	bool ksz87xx_eee_link_erratum;
 	const struct ksz_mib_names *mib_names;
 	int mib_cnt;
-- 
2.34.1

Re: [PATCH net v7 3/3] net: dsa: microchip: monitor potential faults in half-duplex mode

[Andrew Lunn]

On Fri, Jun 21, 2024 at 04:43:22PM +0200, Enguerrand de Ribaucourt wrote:
> The errata DS80000754 recommends monitoring potential faults in
> half-duplex mode for the KSZ9477 family.
> 
> half-duplex is not very common so I just added a critical message
> when the fault conditions are detected. The switch can be expected
> to be unable to communicate anymore in these states and a software
> reset of the switch would be required which I did not implement.
> 
> Fixes: b987e98e50ab ("dsa: add DSA switch driver for Microchip KSZ9477")
> Signed-off-by: Enguerrand de Ribaucourt <enguerrand.de-ribaucourt@savoirfairelinux.com>

Reviewed-by: Andrew Lunn <andrew@lunn.ch>

    Andrew

Re: [PATCH net v7 0/3] Handle new Microchip KSZ 9897 Errata

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net.git (main)
by David S. Miller <davem@davemloft.net>:

On Fri, 21 Jun 2024 16:43:19 +0200 you wrote:
> These patches implement some suggested workarounds from the Microchip KSZ 9897
> Errata [1].
> 
> [1] https://ww1.microchip.com/downloads/aemDocuments/documents/UNG/ProductDocuments/Errata/KSZ9897R-Errata-DS80000758.pdf
> 
> ---
> v7:
>  - use dev_crit_once instead of dev_crit_ratelimited
>  - add a comment to help users understand the consequences of half-duplex errors
> v6: https://lore.kernel.org/netdev/20240614094642.122464-1-enguerrand.de-ribaucourt@savoirfairelinux.com/
>  - remove KSZ9897 phy_id workaround (was a configuration issue)
>  - use macros for checking link down in monitoring function
>  - check if VLAN is enabled before monitoring resources
> v5: https://lore.kernel.org/all/20240604092304.314636-1-enguerrand.de-ribaucourt@savoirfairelinux.com/
>  - use macros for bitfields
>  - rewrap comments
>  - check ksz_pread* return values
>  - fix spelling mistakes
>  - remove KSZ9477 suspend/resume deletion patch
> v4: https://lore.kernel.org/all/20240531142430.678198-1-enguerrand.de-ribaucourt@savoirfairelinux.com/
>  - Rebase on net/main
>  - Add Fixes: tags to the patches
>  - reverse x-mas tree order
>  - use pseudo phy_id instead of match_phy_device
> v3: https://lore.kernel.org/all/20240530102436.226189-1-enguerrand.de-ribaucourt@savoirfairelinux.com/

Here is the summary with links:
  - [net,v7,1/3] net: phy: micrel: add Microchip KSZ 9477 to the device table
    https://git.kernel.org/netdev/net/c/54a4e5c16382
  - [net,v7,2/3] net: dsa: microchip: use collision based back pressure mode
    https://git.kernel.org/netdev/net/c/d963c95bc984
  - [net,v7,3/3] net: dsa: microchip: monitor potential faults in half-duplex mode
    https://git.kernel.org/netdev/net/c/bf1bff11e497

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html

Re: [PATCH net v7 3/3] net: dsa: microchip: monitor potential faults in half-duplex mode

[Russell King (Oracle)]

On Fri, Jun 21, 2024 at 04:43:22PM +0200, Enguerrand de Ribaucourt wrote:
> The errata DS80000754 recommends monitoring potential faults in
> half-duplex mode for the KSZ9477 family.
> 
> half-duplex is not very common so I just added a critical message
> when the fault conditions are detected. The switch can be expected
> to be unable to communicate anymore in these states and a software
> reset of the switch would be required which I did not implement.
> 
> Fixes: b987e98e50ab ("dsa: add DSA switch driver for Microchip KSZ9477")
> Signed-off-by: Enguerrand de Ribaucourt <enguerrand.de-ribaucourt@savoirfairelinux.com>
> ---
> v7:
>  - use dev_crit_once instead of dev_crit_ratelimited
>    The condition will remain true forever and the routine called every
>    5 seconds. There's no need to repeat the message.
>  - add explanations in the comment above the warning to help users
>    anticipate the consequences of the fault.
> v6: https://lore.kernel.org/netdev/20240614094642.122464-4-enguerrand.de-ribaucourt@savoirfairelinux.com/
>  - use macros for PORT_INTF_SPEED_MASK check
>  - add VLAN condition before checking the resources
> v5: https://lore.kernel.org/all/20240604092304.314636-5-enguerrand.de-ribaucourt@savoirfairelinux.com/
>  - use macros for bitmasks
>  - check for return values on ksz_pread*
> v4: https://lore.kernel.org/all/20240531142430.678198-6-enguerrand.de-ribaucourt@savoirfairelinux.com/
>  - rebase on net/main
>  - add Fixes tag
>  - reverse x-mas tree
> v3: https://lore.kernel.org/all/20240530102436.226189-6-enguerrand.de-ribaucourt@savoirfairelinux.com/
> ---
>  drivers/net/dsa/microchip/ksz9477.c     | 51 +++++++++++++++++++++++++
>  drivers/net/dsa/microchip/ksz9477.h     |  2 +
>  drivers/net/dsa/microchip/ksz9477_reg.h | 10 ++++-
>  drivers/net/dsa/microchip/ksz_common.c  | 11 ++++++
>  drivers/net/dsa/microchip/ksz_common.h  |  1 +
>  5 files changed, 73 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/dsa/microchip/ksz9477.c b/drivers/net/dsa/microchip/ksz9477.c
> index c2878dd0ad7e..6924b3818357 100644
> --- a/drivers/net/dsa/microchip/ksz9477.c
> +++ b/drivers/net/dsa/microchip/ksz9477.c
> @@ -429,6 +429,57 @@ void ksz9477_freeze_mib(struct ksz_device *dev, int port, bool freeze)
>  	mutex_unlock(&p->mib.cnt_mutex);
>  }
>  
> +int ksz9477_errata_monitor(struct ksz_device *dev, int port,
> +			   u64 tx_late_col)
> +{
> +	u32 pmavbc;
> +	u8 status;
> +	u16 pqm;
> +	int ret;
> +
> +	ret = ksz_pread8(dev, port, REG_PORT_STATUS_0, &status);
> +	if (ret)
> +		return ret;
> +	if (!(FIELD_GET(PORT_INTF_SPEED_MASK, status) == PORT_INTF_SPEED_NONE) &&
> +	    !(status & PORT_INTF_FULL_DUPLEX)) {
> +		/* Errata DS80000754 recommends monitoring potential faults in
> +		 * half-duplex mode. The switch might not be able to communicate anymore
> +		 * in these states.
> +		 * If you see this message, please read the errata-sheet for more information:

While I realise that the URL is long, netdev still prefers lines to be
no longer than 80 characters, so please wrap the comment accordingly.
The URL is probably fine (since there isn't any option), and then
dev_warn_once() string shouldn't be broken over separate lones either.

However, also consider whether moving this code block into a function
would tidy things up - the compiler can automatically  inline static
functions (and does in many cases, especially when they only have one
callsite.)

-- 
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