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Date:   Sun, 20 Mar 2022 17:14:22 +0000
From:   Jonathan Cameron <jic23@kernel.org>
To:     Jagath Jog J <jagathjog1996@gmail.com>
Cc:     dan@dlrobertson.com, andy.shevchenko@gmail.com,
        linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1 1/5] iio: accel: bma400: conversion to device-managed
 function
Message-ID: <20220320171422.614a4f25@jic23-huawei>
In-Reply-To: <20220319181023.8090-2-jagathjog1996@gmail.com>
References: <20220319181023.8090-1-jagathjog1996@gmail.com>
        <20220319181023.8090-2-jagathjog1996@gmail.com>
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On Sat, 19 Mar 2022 23:40:19 +0530
Jagath Jog J <jagathjog1996@gmail.com> wrote:

> This is a conversion to device-managed by using devm_iio_device_register
> inside probe function, now disabling the regulator and putting bma400 to
> power down via a devm_add_action_or_reset() hook.
> 
> The dev_set_drvdata() call, bma400_remove() function and hooks in the I2C
> and SPI driver struct is removed as devm_iio_device_register function is
> used to automatically unregister on driver detach.
> 
> Signed-off-by: Jagath Jog J <jagathjog1996@gmail.com>

Hi Jagath,

There is an oddity in the existing driver that has lead this in
what I think is the wrong direction.  See below.

> ---
>  drivers/iio/accel/bma400.h      |  2 --
>  drivers/iio/accel/bma400_core.c | 39 ++++++++++++++-------------------
>  drivers/iio/accel/bma400_i2c.c  |  8 -------
>  drivers/iio/accel/bma400_spi.c  |  8 -------
>  4 files changed, 17 insertions(+), 40 deletions(-)
> 
> diff --git a/drivers/iio/accel/bma400.h b/drivers/iio/accel/bma400.h
> index c4c8d74155c2..e938da5a57b4 100644
> --- a/drivers/iio/accel/bma400.h
> +++ b/drivers/iio/accel/bma400.h
> @@ -94,6 +94,4 @@ extern const struct regmap_config bma400_regmap_config;
>  
>  int bma400_probe(struct device *dev, struct regmap *regmap, const char *name);
>  
> -void bma400_remove(struct device *dev);
> -
>  #endif
> diff --git a/drivers/iio/accel/bma400_core.c b/drivers/iio/accel/bma400_core.c
> index fd2647b728d3..dcc7549c7a0e 100644
> --- a/drivers/iio/accel/bma400_core.c
> +++ b/drivers/iio/accel/bma400_core.c
> @@ -793,6 +793,19 @@ static const struct iio_info bma400_info = {
>  	.write_raw_get_fmt = bma400_write_raw_get_fmt,
>  };
>  
> +static void bma400_disable(void *data_ptr)
> +{
> +	struct bma400_data *data = data_ptr;
> +	int ret;
> +
> +	ret = bma400_set_power_mode(data, POWER_MODE_SLEEP);
> +	if (ret)
> +		dev_warn(data->dev, "Failed to put device into sleep mode (%pe)\n",
> +			 ERR_PTR(ret));
> +
> +	regulator_bulk_disable(ARRAY_SIZE(data->regulators), data->regulators);

So this raised alarm bells.  You almost never want a devm callback to do two things.

The reason it 'looks' like this might be ok is that the driver is currently calling
bma400_set_power_mode(data, POWER_MODE_SLEEP) in error paths during probe.
I think it should be.  If you make that modification first you'll see that to
keep a clean: "only undo things you have done" approach you'll then need
to have a pair of devm_add_action_or_reset() callbacks so as to cover the
disabling of the regulators when the power enabling fails and then to
cover the change to sleep mode if anything else fails.


Jonathan

> +}
> +
>  int bma400_probe(struct device *dev, struct regmap *regmap, const char *name)
>  {
>  	struct iio_dev *indio_dev;
> @@ -822,31 +835,13 @@ int bma400_probe(struct device *dev, struct regmap *regmap, const char *name)
>  	indio_dev->num_channels = ARRAY_SIZE(bma400_channels);
>  	indio_dev->modes = INDIO_DIRECT_MODE;
>  
> -	dev_set_drvdata(dev, indio_dev);
> -
> -	return iio_device_register(indio_dev);
> -}
> -EXPORT_SYMBOL(bma400_probe);
> -
> -void bma400_remove(struct device *dev)
> -{
> -	struct iio_dev *indio_dev = dev_get_drvdata(dev);
> -	struct bma400_data *data = iio_priv(indio_dev);
> -	int ret;
> -
> -	mutex_lock(&data->mutex);
> -	ret = bma400_set_power_mode(data, POWER_MODE_SLEEP);
> -	mutex_unlock(&data->mutex);
> -
> +	ret = devm_add_action_or_reset(dev, bma400_disable, data);
>  	if (ret)
> -		dev_warn(dev, "Failed to put device into sleep mode (%pe)\n", ERR_PTR(ret));
> -
> -	regulator_bulk_disable(ARRAY_SIZE(data->regulators),
> -			       data->regulators);
> +		return ret;
>  
> -	iio_device_unregister(indio_dev);
> +	return devm_iio_device_register(dev, indio_dev);
>  }
> -EXPORT_SYMBOL(bma400_remove);
> +EXPORT_SYMBOL(bma400_probe);
>  
>  MODULE_AUTHOR("Dan Robertson <dan@dlrobertson.com>");
>  MODULE_DESCRIPTION("Bosch BMA400 triaxial acceleration sensor core");
> diff --git a/drivers/iio/accel/bma400_i2c.c b/drivers/iio/accel/bma400_i2c.c
> index f50df5310beb..56da06537562 100644
> --- a/drivers/iio/accel/bma400_i2c.c
> +++ b/drivers/iio/accel/bma400_i2c.c
> @@ -27,13 +27,6 @@ static int bma400_i2c_probe(struct i2c_client *client,
>  	return bma400_probe(&client->dev, regmap, id->name);
>  }
>  
> -static int bma400_i2c_remove(struct i2c_client *client)
> -{
> -	bma400_remove(&client->dev);
> -
> -	return 0;
> -}
> -
>  static const struct i2c_device_id bma400_i2c_ids[] = {
>  	{ "bma400", 0 },
>  	{ }
> @@ -52,7 +45,6 @@ static struct i2c_driver bma400_i2c_driver = {
>  		.of_match_table = bma400_of_i2c_match,
>  	},
>  	.probe    = bma400_i2c_probe,
> -	.remove   = bma400_i2c_remove,
>  	.id_table = bma400_i2c_ids,
>  };
>  
> diff --git a/drivers/iio/accel/bma400_spi.c b/drivers/iio/accel/bma400_spi.c
> index 9f622e37477b..96dc9c215401 100644
> --- a/drivers/iio/accel/bma400_spi.c
> +++ b/drivers/iio/accel/bma400_spi.c
> @@ -87,13 +87,6 @@ static int bma400_spi_probe(struct spi_device *spi)
>  	return bma400_probe(&spi->dev, regmap, id->name);
>  }
>  
> -static int bma400_spi_remove(struct spi_device *spi)
> -{
> -	bma400_remove(&spi->dev);
> -
> -	return 0;
> -}
> -
>  static const struct spi_device_id bma400_spi_ids[] = {
>  	{ "bma400", 0 },
>  	{ }
> @@ -112,7 +105,6 @@ static struct spi_driver bma400_spi_driver = {
>  		.of_match_table = bma400_of_spi_match,
>  	},
>  	.probe    = bma400_spi_probe,
> -	.remove   = bma400_spi_remove,
>  	.id_table = bma400_spi_ids,
>  };
>