[PATCH] net: dsa: mv88e6xxx: Avoid EEPROM timeout when EEPROM is absent

[Fabio Estevam]

From: Fabio Estevam <festevam@xxxxxxx>

Since commit 23d775f12dcd ("net: dsa: mv88e6xxx: Wait for EEPROM done
before HW reset") the following error is seen on a imx8mn board with
a 88E6320 switch:

mv88e6085 30be0000.ethernet-1:00: Timeout waiting for EEPROM done

This board does not have an EEPROM attached to the switch though.

This problem is well explained by Andrew Lunn:

"If there is an EEPROM, and the EEPROM contains a lot of data, it could
be that when we perform a hardware reset towards the end of probe, it
interrupts an I2C bus transaction, leaving the I2C bus in a bad state,
and future reads of the EEPROM do not work.

The work around for this was to poll the EEInt status and wait for it
to go true before performing the hardware reset.

However, we have discovered that for some boards which do not have an
EEPROM, EEInt never indicates complete. As a result,
mv88e6xxx_g1_wait_eeprom_done() spins for a second and then prints a
warning.

We probably need a different solution than calling
mv88e6xxx_g1_wait_eeprom_done(). The datasheet for 6352 documents the
EEPROM Command register:

bit 15 is:

  EEPROM Unit Busy. This bit must be set to a one to start an EEPROM
  operation (see EEOp below). Only one EEPROM operation can be
  executing at one time so this bit must be zero before setting it to
  a one.  When the requested EEPROM operation completes this bit will
  automatically be cleared to a zero. The transition of this bit from
  a one to a zero can be used to generate an interrupt (the EEInt in
  Global 1, offset 0x00).

and more interesting is bit 11:

  Register Loader Running. This bit is set to one whenever the
  register loader is busy executing instructions contained in the
  EEPROM."

Change to calling mv88e6xxx_g1_wait_eeprom_done() to fix the timeout
error when the EEPROM chip is not present.
  
Fixes: 23d775f12dcd ("net: dsa: mv88e6xxx: Wait for EEPROM done before HW reset")
Suggested-by: Andrew Lunn <andrew@xxxxxxx>
Signed-off-by: Fabio Estevam <festevam@xxxxxxx>
---
Alfred,

Please test it, if you have a chance. I want to be sure that your usecase
still works well.

 drivers/net/dsa/mv88e6xxx/chip.c    | 6 ++++--
 drivers/net/dsa/mv88e6xxx/global2.c | 2 +-
 drivers/net/dsa/mv88e6xxx/global2.h | 2 ++
 3 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
index a73008b9e0b3..ba906dfab055 100644
--- a/drivers/net/dsa/mv88e6xxx/chip.c
+++ b/drivers/net/dsa/mv88e6xxx/chip.c
@@ -3012,14 +3012,16 @@ static void mv88e6xxx_hardware_reset(struct mv88e6xxx_chip *chip)
 		 * from the wrong location resulting in the switch booting
 		 * to wrong mode and inoperable.
 		 */
-		mv88e6xxx_g1_wait_eeprom_done(chip);
+		if (chip->info->ops->get_eeprom)
+			mv88e6xxx_g2_eeprom_wait(chip);
 
 		gpiod_set_value_cansleep(gpiod, 1);
 		usleep_range(10000, 20000);
 		gpiod_set_value_cansleep(gpiod, 0);
 		usleep_range(10000, 20000);
 
-		mv88e6xxx_g1_wait_eeprom_done(chip);
+		if (chip->info->ops->get_eeprom)
+			mv88e6xxx_g2_eeprom_wait(chip);
 	}
 }
 
diff --git a/drivers/net/dsa/mv88e6xxx/global2.c b/drivers/net/dsa/mv88e6xxx/global2.c
index ec49939968fa..ac302a935ce6 100644
--- a/drivers/net/dsa/mv88e6xxx/global2.c
+++ b/drivers/net/dsa/mv88e6xxx/global2.c
@@ -340,7 +340,7 @@ int mv88e6xxx_g2_pot_clear(struct mv88e6xxx_chip *chip)
  * Offset 0x15: EEPROM Addr (for 8-bit data access)
  */
 
-static int mv88e6xxx_g2_eeprom_wait(struct mv88e6xxx_chip *chip)
+int mv88e6xxx_g2_eeprom_wait(struct mv88e6xxx_chip *chip)
 {
 	int bit = __bf_shf(MV88E6XXX_G2_EEPROM_CMD_BUSY);
 	int err;
diff --git a/drivers/net/dsa/mv88e6xxx/global2.h b/drivers/net/dsa/mv88e6xxx/global2.h
index c05fad5c9f19..6d8d38944b23 100644
--- a/drivers/net/dsa/mv88e6xxx/global2.h
+++ b/drivers/net/dsa/mv88e6xxx/global2.h
@@ -360,6 +360,8 @@ int mv88e6xxx_g2_trunk_clear(struct mv88e6xxx_chip *chip);
 int mv88e6xxx_g2_device_mapping_write(struct mv88e6xxx_chip *chip, int target,
 				      int port);
 
+int mv88e6xxx_g2_eeprom_wait(struct mv88e6xxx_chip *chip);
+
 extern const struct mv88e6xxx_irq_ops mv88e6097_watchdog_ops;
 extern const struct mv88e6xxx_irq_ops mv88e6250_watchdog_ops;
 extern const struct mv88e6xxx_irq_ops mv88e6390_watchdog_ops;
-- 
2.34.1