hwmon: pmbus: Fix -EIO seen on pli1209

After doing performance optimizations the pli1209 driver failed to
probe with a probabilty of 2%. It wasn't able to read the PMBUS_OPERATION
register due to an -EIO error.

An investigation showed that the PLI1209 takes 230 usec to execute the
CLEAR_FAULTS command. During that time it's busy and NACKs all requests
on the SMBUS interface. It also NACKs reads on PMBUS_STATUS_BYTE
making it impossible to poll the BUSY flag.

Add a custom write_data function to just wait for not BUSY unconditionally
after sending a CLEAR_FAULTS command.

TEST: Verified using an I2C bus analyser that no more NACKs are seen after
      sending a CLEAR_FAULTS command.

Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Signed-off-by: Naresh Solanki <Naresh.Solanki@9elements.com>
Link: https://lore.kernel.org/r/20230817092527.808631-3-Naresh.Solanki@9elements.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

diff --git a/drivers/hwmon/pmbus/pli1209bc.c b/drivers/hwmon/pmbus/pli1209bc.c
index 7d8bd3167b213ebb40c14142c00fb970691ef357..c95433790b11107e1afbca3b2d6ce959e7611f44 100644 (file)
--- a/drivers/hwmon/pmbus/pli1209bc.c
+++ b/drivers/hwmon/pmbus/pli1209bc.c
@@ -5,6 +5,7 @@
  * Copyright (c) 2022 9elements GmbH
  */
 
+#include <linux/delay.h>
 #include <linux/i2c.h>
 #include <linux/module.h>
 #include <linux/pmbus.h>
@@ -53,6 +54,30 @@ static int pli1209bc_read_word_data(struct i2c_client *client, int page,
        }
 }
 
+static int pli1209bc_write_byte(struct i2c_client *client, int page, u8 reg)
+{
+       int ret;
+
+       switch (reg) {
+       case PMBUS_CLEAR_FAULTS:
+               ret = pmbus_write_byte(client, page, reg);
+               /*
+                * PLI1209 takes 230 usec to execute the CLEAR_FAULTS command.
+                * During that time it's busy and NACKs all requests on the
+                * SMBUS interface. It also NACKs reads on PMBUS_STATUS_BYTE
+                * making it impossible to poll the BUSY flag.
+                *
+                * Just wait for not BUSY unconditionally.
+                */
+               usleep_range(250, 300);
+               break;
+       default:
+               ret = -ENODATA;
+               break;
+       }
+       return ret;
+}
+
 #if IS_ENABLED(CONFIG_SENSORS_PLI1209BC_REGULATOR)
 static const struct regulator_desc pli1209bc_reg_desc = {
        .name = "vout2",
@@ -102,6 +127,7 @@ static struct pmbus_driver_info pli1209bc_info = {
            | PMBUS_HAVE_TEMP | PMBUS_HAVE_STATUS_TEMP
            | PMBUS_HAVE_STATUS_IOUT | PMBUS_HAVE_STATUS_INPUT,
        .read_word_data = pli1209bc_read_word_data,
+       .write_byte = pli1209bc_write_byte,
 #if IS_ENABLED(CONFIG_SENSORS_PLI1209BC_REGULATOR)
        .num_regulators = 1,
        .reg_desc = &pli1209bc_reg_desc,