On Sat, May 22, 2021 at 3:41 PM Guenter Roeck [off-list ref] wrote:

On 5/22/21 3:55 AM, Erik Rosen wrote:

quoted

Add support for reading and decoding direct format coefficients to
the PMBus core driver. If the new flag PMBUS_USE_COEFFICIENTS_CMD
is set, the driver will use the COEFFICIENTS register together with
the information in the pmbus_sensor_attr structs to initialize
relevant coefficients for the direct mode format.

Signed-off-by: Erik Rosen <redacted>
---
  drivers/hwmon/pmbus/pmbus_core.c | 93 ++++++++++++++++++++++++++++++++
  include/linux/pmbus.h            |  8 +++
  2 files changed, 101 insertions(+)

diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
index 460cbfd716e4..03c169bf5633 100644
--- a/drivers/hwmon/pmbus/pmbus_core.c
+++ b/drivers/hwmon/pmbus/pmbus_core.c

@@ -2177,6 +2177,38 @@ static int pmbus_find_attributes(struct i2c_client *client,
      return ret;
  }

+static int pmbus_init_coefficients(struct i2c_client *client,
+                                struct pmbus_data *data, int page,

This seems wrong. Coefficients are not maintained per page but per class,
and (re-)reading them for each supported page doesn't really add value or
even make sense.

quoted

+                                enum pmbus_sensor_classes sensor_class,
+                                const struct pmbus_sensor_attr *attrs,
+                                int nattrs)
+{
+     int i, status;
+
+     for (i = 0; i < nattrs; i++) {
+             if (attrs->class == sensor_class &&
+                 (attrs->func & data->info->func[page])) {
+                     status = pmbus_read_coefficients(client,
+                                                      (struct pmbus_driver_info *)data->info,
+                                                      sensor_class,
+                                                      attrs->reg);
+                     if (status < 0) {
+                             dev_err(&client->dev,
+                                     "Failed to read coefficients for register: %x\n",
+                                     attrs->reg);
+                             return status;
+                     }
+                     return 0;
+             }
+             attrs++;
+     }
+
+     dev_err(&client->dev, "No coefficients found for register: %x\n",
+             attrs->reg);
+

attrs points beyond the array size here, so attrs->reg does not point
to a valid array element. The problem would also not be the register
this happens to point to, but the class (ie the chip does not support
a sensor of the requested class).

Not sure if this should trigger a message or error in the first place.
It won't matter since the chip will never need those coefficients.
If anything, this would be a misconfiguration (the driver should
not set direct format for this sensor class), and the return value
should be -EINVAL.

Either case, I wonder if this can be handled with less complex code,
ie without having to check data->info->func[] for all pages. How
about just walking through attrs and try all class matches until
one is found that works (ie not return on error but keep trying) ?

Ok, I'll send a new version based on your comments.
I'm not entirely comfortable with just silently ignoring any failure to
retrieve the coefficients for a sensor class. I mean it could be due to any
reason; a bus error for instance. I'll return a -EINVAL for now if you don't
disagree.

/Erik

quoted

+     return -ENODEV;
+}
+
  /*
   * Identify chip parameters.
   * This function is called for all chips.

@@ -2185,6 +2217,7 @@ static int pmbus_identify_common(struct i2c_client *client,
                               struct pmbus_data *data, int page)
  {
      int vout_mode = -1;
+     int ret;

      if (pmbus_check_byte_register(client, page, PMBUS_VOUT_MODE))
              vout_mode = _pmbus_read_byte_data(client, page,

@@ -2214,6 +2247,66 @@ static int pmbus_identify_common(struct i2c_client *client,
              }
      }

+     if (data->flags & PMBUS_USE_COEFFICIENTS_CMD) {

I think there should be a separate function to handle that,
to be called only once, not once per page.

quoted

+             if (!i2c_check_functionality(client->adapter,
+                                          I2C_FUNC_SMBUS_BLOCK_PROC_CALL))
+                     return -ENODEV;
+
+             if (data->info->format[PSC_VOLTAGE_IN] == direct) {
+                     ret = pmbus_init_coefficients(client, data, page,
+                                                   PSC_VOLTAGE_IN,
+                                                   voltage_attributes,
+                                                   ARRAY_SIZE(voltage_attributes));
+                     if (ret)
+                             return ret;
+             }

It might be useful to have a little structure with {class, attribute list pointer,
attribute list size} and walk through that in a loop instead of repeating essentially
the same code multiple times.

quoted

+
+             if (data->info->format[PSC_VOLTAGE_OUT] == direct) {
+                     ret = pmbus_init_coefficients(client, data, page,
+                                                   PSC_VOLTAGE_OUT,
+                                                   voltage_attributes,
+                                                   ARRAY_SIZE(voltage_attributes));
+                     if (ret)
+                             return ret;
+             }
+
+             if (data->info->format[PSC_CURRENT_IN] == direct) {
+                     ret = pmbus_init_coefficients(client, data, page,
+                                                   PSC_CURRENT_IN,
+                                                   current_attributes,
+                                                   ARRAY_SIZE(current_attributes));
+                     if (ret)
+                             return ret;
+             }
+
+             if (data->info->format[PSC_CURRENT_OUT] == direct) {
+                     ret = pmbus_init_coefficients(client, data, page,
+                                                   PSC_CURRENT_OUT,
+                                                   current_attributes,
+                                                   ARRAY_SIZE(current_attributes));
+                     if (ret)
+                             return ret;
+             }
+
+             if (data->info->format[PSC_POWER] == direct) {
+                     ret = pmbus_init_coefficients(client, data, page,
+                                                   PSC_POWER,
+                                                   power_attributes,
+                                                   ARRAY_SIZE(power_attributes));
+                     if (ret)
+                             return ret;
+             }
+
+             if (data->info->format[PSC_TEMPERATURE] == direct) {
+                     ret = pmbus_init_coefficients(client, data, page,
+                                                   PSC_TEMPERATURE,
+                                                   temp_attributes,
+                                                   ARRAY_SIZE(temp_attributes));
+                     if (ret)
+                             return ret;
+             }
+     }
+
      pmbus_clear_fault_page(client, page);
      return 0;
  }

diff --git a/include/linux/pmbus.h b/include/linux/pmbus.h
index f720470b1bab..7fdc282dab5a 100644
--- a/include/linux/pmbus.h
+++ b/include/linux/pmbus.h

@@ -52,6 +52,14 @@
   */
  #define PMBUS_NO_WRITE_PROTECT                      BIT(4)

+/*
+ * PMBUS_USE_COEFFICIENTS_CMD
+ *
+ * When this flag is set the PMBus core driver will use the COEFFICIENTS
+ * register to initialize the coefficients for the direct mode format.
+ */
+#define PMBUS_USE_COEFFICIENTS_CMD           BIT(5)
+
  struct pmbus_platform_data {
      u32 flags;              /* Device specific flags */