hwmon: (adt7470) fix checking of num_temp_sensors

hwmon: (adt7470) fix checking of num_temp_sensors

[Martin Etnestad]

The ADT7470 driver uses num_temp_sensors to check whether or not it
actually needs to read the temperature registers. However, the check
currently has a broken comparison: "num_temp_sensors >= 0" instead of
"num_temp_sensors == 0".

This causes the driver to only read the temperature registers _once_
because num_temp_sensors gets set to a non-negative number after the
check, in the same function.

Additionally, the check is currently done _after_ the measurement
sequence has been completed. The check should be done before the
measurement sequence is initiated, as it can be skipped altogether if
num_temp_sensors is 0.

This patch fixes the comparison and moves the check.

Signed-off-by: Martin Etnestad <martin.etnestad@appeartv.com>
---
  drivers/hwmon/adt7470.c | 8 ++++----
  1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/hwmon/adt7470.c b/drivers/hwmon/adt7470.c
index f5da39a..d1f9a54 100644
--- a/drivers/hwmon/adt7470.c
+++ b/drivers/hwmon/adt7470.c
@@ -201,6 +201,10 @@ static int adt7470_read_temperatures(struct 
i2c_client *client,
      int i;
      u8 cfg, pwm[4], pwm_cfg[2];

+    /* only read sensors if we have to */
+    if (data->num_temp_sensors == 0)
+        return 0;
+
      /* save pwm[1-4] config register */
      pwm_cfg[0] = i2c_smbus_read_byte_data(client, ADT7470_REG_PWM_CFG(0));
      pwm_cfg[1] = i2c_smbus_read_byte_data(client, ADT7470_REG_PWM_CFG(2));
@@ -243,10 +247,6 @@ static int adt7470_read_temperatures(struct 
i2c_client *client,
          return -EAGAIN;
      }

-    /* Only count fans if we have to */
-    if (data->num_temp_sensors >= 0)
-        return 0;
-
      for (i = 0; i < ADT7470_TEMP_COUNT; i++) {
          data->temp[i] = i2c_smbus_read_byte_data(client,
                          ADT7470_TEMP_REG(i));
-- 
2.7.4

Re: hwmon: (adt7470) fix checking of num_temp_sensors

[Martin Etnestad]

Hi again,

Please disregard this patch!

I just saw that I had missed how adt7470_update_device() relies on 
adt7470_read_temperatures().
In that context, the current code is working correctly.

And so I very humbly apologize for submitting a garbage patch.. Sorry!

     -Martin


On 11/23/2016 12:34 PM, Martin Etnestad wrote:
> The ADT7470 driver uses num_temp_sensors to check whether or not it
> actually needs to read the temperature registers. However, the check
> currently has a broken comparison: "num_temp_sensors >= 0" instead of
> "num_temp_sensors == 0".
>
> This causes the driver to only read the temperature registers _once_
> because num_temp_sensors gets set to a non-negative number after the
> check, in the same function.
>
> Additionally, the check is currently done _after_ the measurement
> sequence has been completed. The check should be done before the
> measurement sequence is initiated, as it can be skipped altogether if
> num_temp_sensors is 0.
>
> This patch fixes the comparison and moves the check.
>
> Signed-off-by: Martin Etnestad <martin.etnestad@appeartv.com>
> ---
>  drivers/hwmon/adt7470.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/hwmon/adt7470.c b/drivers/hwmon/adt7470.c
> index f5da39a..d1f9a54 100644
> --- a/drivers/hwmon/adt7470.c
> +++ b/drivers/hwmon/adt7470.c
> @@ -201,6 +201,10 @@ static int adt7470_read_temperatures(struct 
> i2c_client *client,
>      int i;
>      u8 cfg, pwm[4], pwm_cfg[2];
>
> +    /* only read sensors if we have to */
> +    if (data->num_temp_sensors == 0)
> +        return 0;
> +
>      /* save pwm[1-4] config register */
>      pwm_cfg[0] = i2c_smbus_read_byte_data(client, 
> ADT7470_REG_PWM_CFG(0));
>      pwm_cfg[1] = i2c_smbus_read_byte_data(client, 
> ADT7470_REG_PWM_CFG(2));
> @@ -243,10 +247,6 @@ static int adt7470_read_temperatures(struct 
> i2c_client *client,
>          return -EAGAIN;
>      }
>
> -    /* Only count fans if we have to */
> -    if (data->num_temp_sensors >= 0)
> -        return 0;
> -
>      for (i = 0; i < ADT7470_TEMP_COUNT; i++) {
>          data->temp[i] = i2c_smbus_read_byte_data(client,
>                          ADT7470_TEMP_REG(i));

-- 
Martin Etnestad
R&D Engineer

Email: martin.etnestad@appeartv.com

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Re: hwmon: (adt7470) fix checking of num_temp_sensors

[Guenter Roeck]

On 11/23/2016 03:34 AM, Martin Etnestad wrote:
> The ADT7470 driver uses num_temp_sensors to check whether or not it
> actually needs to read the temperature registers. However, the check
> currently has a broken comparison: "num_temp_sensors >= 0" instead of
> "num_temp_sensors == 0".
>
> This causes the driver to only read the temperature registers _once_
> because num_temp_sensors gets set to a non-negative number after the
> check, in the same function.
>
> Additionally, the check is currently done _after_ the measurement
> sequence has been completed. The check should be done before the
> measurement sequence is initiated, as it can be skipped altogether if
> num_temp_sensors is 0.
>

The check is there to ensure that num_temp_sensors is calculated only once.
Your change breaks that. After the initial probe, temperature sensor
values are read in adt7470_update_device(), and it is no longer necessary
to do the read from adt7470_read_temperatures().

NACK, sorry.

Guenter

> This patch fixes the comparison and moves the check.
>
> Signed-off-by: Martin Etnestad <martin.etnestad@appeartv.com>
> ---
>  drivers/hwmon/adt7470.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/hwmon/adt7470.c b/drivers/hwmon/adt7470.c
> index f5da39a..d1f9a54 100644
> --- a/drivers/hwmon/adt7470.c
> +++ b/drivers/hwmon/adt7470.c
> @@ -201,6 +201,10 @@ static int adt7470_read_temperatures(struct i2c_client *client,
>      int i;
>      u8 cfg, pwm[4], pwm_cfg[2];
>
> +    /* only read sensors if we have to */
> +    if (data->num_temp_sensors == 0)
> +        return 0;
> +
>      /* save pwm[1-4] config register */
>      pwm_cfg[0] = i2c_smbus_read_byte_data(client, ADT7470_REG_PWM_CFG(0));
>      pwm_cfg[1] = i2c_smbus_read_byte_data(client, ADT7470_REG_PWM_CFG(2));
> @@ -243,10 +247,6 @@ static int adt7470_read_temperatures(struct i2c_client *client,
>          return -EAGAIN;
>      }
>
> -    /* Only count fans if we have to */
> -    if (data->num_temp_sensors >= 0)
> -        return 0;
> -
>      for (i = 0; i < ADT7470_TEMP_COUNT; i++) {
>          data->temp[i] = i2c_smbus_read_byte_data(client,
>                          ADT7470_TEMP_REG(i));