linux-kernel - [PATCH v2] net: dsa: mv88e6xxx: fix external smi for mv88e6176

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Message-Id: <20250616162023.2795566-1-quantumcross@gmail.com>
Date: Mon, 16 Jun 2025 12:20:25 -0400
From: Robert Cross <quantumcross@...il.com>
To: netdev@...r.kernel.org
Cc: bpf@...r.kernel.org,
	andrew@...n.ch,
	olteanv@...il.com,
	davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	linux-kernel@...r.kernel.org,
	Robert Cross <quantumcross@...il.com>
Subject: [PATCH v2] net: dsa: mv88e6xxx: fix external smi for mv88e6176

(Sorry this is my second attempt, I fixed my email client)

I was trying to enable external SMI on a mv88e6176.
mv88e6390_g2_scratch_gpio_set_smi() would return -EBUSY when checking
the scratch register Config DATA2 p0 mode to ensure that the external
smi pins are free, but on my device, bit 4 of p0_mode was always 1,
even if the port was completely disabled.

Unless someone with the datasheet can prove me wrong, I believe that
at least for the 6176, the mode mask here is 3 bits wide, and the
fourth bit is irrelevant or reserved.

To fix this, I add a field in mv88e6xxx_info to denote a
p0_mode_mask_override to use. If this is set to the default
value of 0, then the definition of
MV88E6352_G2_SCRATCH_CONFIG_DATA2_P0_MODE_MASK will be used as normal.

I can confirm that this allows me to use external smi on my mv88e6176!

Fixes: 2510babcfaf0 ("net: dsa: mv88e6xxx: scratch registers and external MDIO pins")
Signed-off-by: Robert Cross <quantumcross@...il.com>
---
 drivers/net/dsa/mv88e6xxx/chip.c            | 1 +
 drivers/net/dsa/mv88e6xxx/chip.h            | 7 +++++++
 drivers/net/dsa/mv88e6xxx/global2_scratch.c | 7 ++++++-
 3 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
index 2281d6ab8c9ab..0fe7b6fc7016c 100644
--- a/drivers/net/dsa/mv88e6xxx/chip.c
+++ b/drivers/net/dsa/mv88e6xxx/chip.c
@@ -6013,6 +6013,7 @@ static const struct mv88e6xxx_info mv88e6xxx_table[] = {
 		.multi_chip = true,
 		.edsa_support = MV88E6XXX_EDSA_SUPPORTED,
 		.ops = &mv88e6176_ops,
+		.p0_mode_mask_override = 0x7,
 	},
 
 	[MV88E6185] = {
diff --git a/drivers/net/dsa/mv88e6xxx/chip.h b/drivers/net/dsa/mv88e6xxx/chip.h
index 7d00482f53a3b..6307c225ce94c 100644
--- a/drivers/net/dsa/mv88e6xxx/chip.h
+++ b/drivers/net/dsa/mv88e6xxx/chip.h
@@ -178,6 +178,13 @@ struct mv88e6xxx_info {
 	 * port 0, 1 means internal PHYs range starts at port 1, etc
 	 */
 	unsigned int internal_phys_offset;
+
+	/* Some chips use 3 bits for the port mode in scratch
+         * register CONFIG Data2.
+         * If this is set to 0x0, it will use the default mask of
+         * MV88E6352_G2_SCRATCH_CONFIG_DATA2_P0_MODE_MASK
+         */
+	u8 p0_mode_mask_override;
 };
 
 struct mv88e6xxx_atu_entry {
diff --git a/drivers/net/dsa/mv88e6xxx/global2_scratch.c b/drivers/net/dsa/mv88e6xxx/global2_scratch.c
index 53a6d3ed63b32..7f1657eba7a4e 100644
--- a/drivers/net/dsa/mv88e6xxx/global2_scratch.c
+++ b/drivers/net/dsa/mv88e6xxx/global2_scratch.c
@@ -255,6 +255,7 @@ int mv88e6390_g2_scratch_gpio_set_smi(struct mv88e6xxx_chip *chip,
 	int config_data1 = MV88E6352_G2_SCRATCH_CONFIG_DATA1;
 	int config_data2 = MV88E6352_G2_SCRATCH_CONFIG_DATA2;
 	bool no_cpu;
+	u8 p0_mode_mask;
 	u8 p0_mode;
 	int err;
 	u8 val;
@@ -263,7 +264,11 @@ int mv88e6390_g2_scratch_gpio_set_smi(struct mv88e6xxx_chip *chip,
 	if (err)
 		return err;
 
-	p0_mode = val & MV88E6352_G2_SCRATCH_CONFIG_DATA2_P0_MODE_MASK;
+	p0_mode_mask = chip->info->p0_mode_mask_override;
+	if( p0_mode_mask == 0x0) {
+		p0_mode_mask = MV88E6352_G2_SCRATCH_CONFIG_DATA2_P0_MODE_MASK;
+	}
+	p0_mode = val & p0_mode_mask;
 
 	if (p0_mode == 0x01 || p0_mode == 0x02)
 		return -EBUSY;
-- 
2.39.5