linux-kernel - Re: [PATCH v2 09/14] staging: iio: ad7746: Add remove()

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Date:   Wed, 18 Apr 2018 16:25:17 -0300
From:   Hernán Gonzalez <hernan@...guardiasur.com.ar>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     knaack.h@....de, lars@...afoo.de,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        gregkh@...uxfoundation.org, Michael.Hennerich@...log.com,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 09/14] staging: iio: ad7746: Add remove()

On Sun, Apr 15, 2018 at 12:31 PM, Jonathan Cameron <jic23@...nel.org> wrote:
> On Fri, 13 Apr 2018 13:36:46 -0300
> Hernán Gonzalez <hernan@...guardiasur.com.ar> wrote:
>
>> This allows the driver to be probed and removed as a module powering it
>> down on remove().
>>
>> Signed-off-by: Hernán Gonzalez <hernan@...guardiasur.com.ar>
>> ---
>>  drivers/staging/iio/cdc/ad7746.c | 26 ++++++++++++++++++++++++++
>>  1 file changed, 26 insertions(+)
>>
>> diff --git a/drivers/staging/iio/cdc/ad7746.c b/drivers/staging/iio/cdc/ad7746.c
>> index c29a221..05506bf9 100644
>> --- a/drivers/staging/iio/cdc/ad7746.c
>> +++ b/drivers/staging/iio/cdc/ad7746.c
>> @@ -775,6 +775,31 @@ static int ad7746_probe(struct i2c_client *client,
>>       return 0;
>>  }
>>
>> +static int ad7746_remove(struct i2c_client *client)
>> +{
>> +     struct iio_dev *indio_dev = i2c_get_clientdata(client);
>> +     struct ad7746_chip_info *chip = iio_priv(indio_dev);
>> +     unsigned char regval;
>> +     int ret;
>> +
>> +     mutex_lock(&chip->lock);
>> +
>> +     regval = chip->config | AD7746_CONF_MODE_PWRDN;
>> +     ret = i2c_smbus_write_byte_data(chip->client, AD7746_REG_CFG, regval);
> As this is a one off operation, perhaps it would be better to factor
> it out to a utility function then use devm_add_action_or_reset in
> the probe?
>
> Also, I am nervous about this change as there doesn't seem to be
> path in probe by which this is deliberately reversed?
> It seems to be 'accidentally' handled by the read_raw write to the
> CFG register.
>
> The data sheet doesn't really mention much about this register
> at all.  It may have special requirements to exit from power down - I have
> no idea, but if it is costless, why do we bother with idle mode?
>
> Perhaps Michael can confirm if this is safe to do or not.
>
>

I guess it'll be better to just drop this until Michael answers. I've
been trying to get a hold of the hw but with no success (or I have to
pay 3 times its cost in shipping), will keep searching though.

>> +
>> +     mutex_unlock(&chip->lock);
>> +
>> +     if (ret < 0) {
>> +             dev_warn(&client->dev, "Could NOT Power Down!\n");
>> +             goto out;
>> +     }
>> +
>> +     iio_device_unregister(indio_dev);
> You can't safely do this against the devm_iio_device_register.
>
>> +
>> +out:
>> +     return ret;
>> +}
>> +
>>  static const struct i2c_device_id ad7746_id[] = {
>>       { "ad7745", 7745 },
>>       { "ad7746", 7746 },
>> @@ -799,6 +824,7 @@ static struct i2c_driver ad7746_driver = {
>>               .of_match_table = of_match_ptr(ad7746_of_match),
>>       },
>>       .probe = ad7746_probe,
>> +     .remove = ad7746_remove,
>>       .id_table = ad7746_id,
>>  };
>>  module_i2c_driver(ad7746_driver);
>