Explicitly disable PEC when the client does not support it.
The problematic scenario is the following. A device with enabled PEC
support is up and running, a kernel driver loaded.
Then the driver is unloaded (or device unbound), the HW device
is reconfigured externally (e.g. by i2cset) to advertise itself as not
supporting PEC. Without a new code, at the second load of the driver
(or bind) the "flags" variable is not updated to avoid PEC usage. As a
consequence the further communication with the device is done with
the PEC enabled, which is wrong.

Signed-off-by: Adam Wujek <dev_public@wujek.eu>
---
 drivers/hwmon/pmbus/pmbus_core.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
index b2618b1d529e..0af7a3d74f47 100644
--- a/drivers/hwmon/pmbus/pmbus_core.c
+++ b/drivers/hwmon/pmbus/pmbus_core.c
@@ -2334,7 +2334,8 @@ static int pmbus_init_common(struct i2c_client *client, struct pmbus_data *data,
 				client->flags |= I2C_CLIENT_PEC;
 			}
 		}
-	}
+	} else
+		client->flags &= ~I2C_CLIENT_PEC;

 	/*
 	 * Check if the chip is write protected. If it is, we can not clear
--
2.25.1

On 4/20/22 05:54, Adam Wujek wrote:
> Explicitly disable PEC when the client does not support it.
> The problematic scenario is the following. A device with enabled PEC
> support is up and running, a kernel driver loaded.
> Then the driver is unloaded (or device unbound), the HW device
> is reconfigured externally (e.g. by i2cset) to advertise itself as not
> supporting PEC. Without a new code, at the second load of the driver
> (or bind) the "flags" variable is not updated to avoid PEC usage. As a
> consequence the further communication with the device is done with
> the PEC enabled, which is wrong.
> 
> Signed-off-by: Adam Wujek <dev_public@wujek.eu>

Subject should start with hwmon:. Please version your patches,
and provide change logs.

> ---
>   drivers/hwmon/pmbus/pmbus_core.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
> index b2618b1d529e..0af7a3d74f47 100644
> --- a/drivers/hwmon/pmbus/pmbus_core.c
> +++ b/drivers/hwmon/pmbus/pmbus_core.c
> @@ -2334,7 +2334,8 @@ static int pmbus_init_common(struct i2c_client *client, struct pmbus_data *data,
>   				client->flags |= I2C_CLIENT_PEC;
>   			}
>   		}
> -	}
> +	} else
> +		client->flags &= ~I2C_CLIENT_PEC;

Since if() is in {}, else should be in {} as well.

Guenter

> 
>   	/*
>   	 * Check if the chip is write protected. If it is, we can not clear
> --
> 2.25.1
> 
>

Explicitly disable PEC when the client does not support it.
The problematic scenario is the following. A device with enabled PEC
support is up and running and a kernel driver is loaded.
Then the driver is unloaded (or device unbound), the HW device
is reconfigured externally (e.g. by i2cset) to advertise itself as not
supporting PEC. Without a new code, at the second load of the driver
(or bind) the "flags" variable is not updated to avoid PEC usage. As a
consequence the further communication with the device is done with
the PEC enabled, which is wrong and may fail.

The implementation first disable the I2C_CLIENT_PEC flag, then the old
code enable it if needed.

Signed-off-by: Adam Wujek <dev_public@wujek.eu>
---
Notes:
    Changes in v2:
    - Rebase to the latest kernel
    - Update commit message

    Changes in v3:
    - Rework the patch, disable the flag first, then enable if needed.
      Adding three else statements to disable the flag will make the code
      less readable.
    - Update commit message

 drivers/hwmon/pmbus/pmbus_core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
index b2618b1d529e..d93574d6a1fb 100644
--- a/drivers/hwmon/pmbus/pmbus_core.c
+++ b/drivers/hwmon/pmbus/pmbus_core.c
@@ -2326,6 +2326,9 @@ static int pmbus_init_common(struct i2c_client *client, struct pmbus_data *data,
 		data->has_status_word = true;
 	}

+	/* Make sure PEC is disabled, will be enabled later if needed */
+	client->flags &= ~I2C_CLIENT_PEC;
+
 	/* Enable PEC if the controller and bus supports it */
 	if (!(data->flags & PMBUS_NO_CAPABILITY)) {
 		ret = i2c_smbus_read_byte_data(client, PMBUS_CAPABILITY);
--
2.25.1