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    Subject[PATCH 5.15 043/135] hwmon: (pmbus) disable PEC if not enabled
    Date
    From: Adam Wujek <dev_public@wujek.eu>

    commit 75d2b2b06bd8407d03a3f126bc8b95eb356906c7 upstream.

    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.

    Fixes: 4e5418f787ec ("hwmon: (pmbus_core) Check adapter PEC support")
    Signed-off-by: Adam Wujek <dev_public@wujek.eu>
    Link: https://lore.kernel.org/r/20220420145059.431061-1-dev_public@wujek.eu
    Signed-off-by: Guenter Roeck <linux@roeck-us.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    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);
    --
    2.36.1


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