linux-kernel - [PATCH net v3] net: dsa: mv88e6xxx: Wait for EEPROM done before HW reset

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Message-ID: <20230815001323.24739-1-l00g33k@gmail.com>
Date:   Mon, 14 Aug 2023 17:13:23 -0700
From:   Alfred Lee <l00g33k@...il.com>
To:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     andrew@...n.ch, olteanv@...il.com, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        sgarzare@...hat.com, AVKrasnov@...rdevices.ru,
        Alfred Lee <l00g33k@...il.com>
Subject: [PATCH net v3] net: dsa: mv88e6xxx: Wait for EEPROM done before HW reset

If the switch is reset during active EEPROM transactions, as in
just after an SoC reset after power up, the I2C bus transaction
may be cut short leaving the EEPROM internal I2C state machine
in the wrong state.  When the switch is reset again, the bad
state machine state may result in data being read from the wrong
memory location causing the switch to enter unexpected mode
rendering it inoperational.

Fixes: a3dcb3e7e70c ("net: dsa: mv88e6xxx: Wait for EEPROM done after HW reset")
Signed-off-by: Alfred Lee <l00g33k@...il.com>
---
 drivers/net/dsa/mv88e6xxx/chip.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
index c7d51a539451..7af2f08a62f1 100644
--- a/drivers/net/dsa/mv88e6xxx/chip.c
+++ b/drivers/net/dsa/mv88e6xxx/chip.c
@@ -3034,6 +3034,14 @@ static void mv88e6xxx_hardware_reset(struct mv88e6xxx_chip *chip)
 
 	/* If there is a GPIO connected to the reset pin, toggle it */
 	if (gpiod) {
+		/* If the switch has just been reset and not yet completed
+		 * loading EEPROM, the reset may interrupt the I2C transaction
+		 * mid-byte, causing the first EEPROM read after the reset
+		 * from the wrong location resulting in the switch booting
+		 * to wrong mode and inoperable.
+		 */
+		mv88e6xxx_g1_wait_eeprom_done(chip);
+
 		gpiod_set_value_cansleep(gpiod, 1);
 		usleep_range(10000, 20000);
 		gpiod_set_value_cansleep(gpiod, 0);
-- 
2.41.0