linux-kernel - Re: [PATCH 1/2] hwmon: (lm90) Add power control

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Message-ID: <5201F138.3080906@roeck-us.net>
Date:	Wed, 07 Aug 2013 00:03:20 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Wei Ni <wni@...dia.com>
CC:	khali@...ux-fr.org, swarren@...dotorg.org, MLongnecker@...dia.com,
	linux-arm-kernel@...ts.infradead.org, lm-sensors@...sensors.org,
	linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org
Subject: Re: [PATCH 1/2] hwmon: (lm90) Add power control

On 08/06/2013 11:52 PM, Wei Ni wrote:
> The device lm90 can be controlled by the vdd rail.
> Adding the power control support to power on/off the vdd rail.
> And make sure that power is enabled before accessing the device.
>
> Signed-off-by: Wei Ni <wni@...dia.com>
> ---
>   drivers/hwmon/lm90.c |   52 ++++++++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 52 insertions(+)
>
> diff --git a/drivers/hwmon/lm90.c b/drivers/hwmon/lm90.c
> index cdff742..eeb0115 100644
> --- a/drivers/hwmon/lm90.c
> +++ b/drivers/hwmon/lm90.c
> @@ -89,6 +89,8 @@
>   #include <linux/err.h>
>   #include <linux/mutex.h>
>   #include <linux/sysfs.h>
> +#include <linux/delay.h>
> +#include <linux/regulator/consumer.h>
>
>   /*
>    * Addresses to scan
> @@ -179,6 +181,8 @@ enum chips { lm90, adm1032, lm99, lm86, max6657, max6659, adt7461, max6680,
>   #define LM90_HAVE_TEMP3		(1 << 6) /* 3rd temperature sensor	*/
>   #define LM90_HAVE_BROKEN_ALERT	(1 << 7) /* Broken alert		*/
>
> +#define POWER_ON_DELAY 20 /*ms*/
> +
>   /*
>    * Driver data (common to all clients)
>    */
> @@ -302,6 +306,7 @@ static const struct lm90_params lm90_params[] = {
>   struct lm90_data {
>   	struct device *hwmon_dev;
>   	struct mutex update_lock;
> +	struct regulator *lm90_reg;
>   	char valid; /* zero until following fields are valid */
>   	unsigned long last_updated; /* in jiffies */
>   	int kind;
> @@ -1391,6 +1396,48 @@ static void lm90_init_client(struct i2c_client *client)
>   		i2c_smbus_write_byte_data(client, LM90_REG_W_CONFIG1, config);
>   }
>
> +static int lm90_power_control(struct i2c_client *client, bool is_enable)
> +{
> +	struct lm90_data *data = i2c_get_clientdata(client);
> +	int ret;
> +
> +	mutex_lock(&data->update_lock);
> +
> +	if (!data->lm90_reg) {
> +		data->lm90_reg = regulator_get(&client->dev, "vdd");
> +		if (IS_ERR_OR_NULL(data->lm90_reg)) {
> +			if (PTR_ERR(data->lm90_reg) == -ENODEV)
> +				dev_info(&client->dev,
> +					 "No regulator found for vdd. Assuming vdd is always powered.");
> +			else
> +				dev_warn(&client->dev,
> +					 "Error [%ld] in getting the regulator handle for vdd.\n",
> +					 PTR_ERR(data->lm90_reg));
> +			data->lm90_reg = NULL;
> +			mutex_unlock(&data->update_lock);
> +			return -ENODEV;

I don't think it is acceptable to have the driver fail on pretty much all PCs.

Also, I dislike that - even if the calling code doesn't fail - the above message would be displayed on unload as well.

In general, the 'unload' flag seems unnecessary. You could just call

	if (data->lm90_reg)
		regulator_disable();

in the remove function. In addition to that, shouldn't you call regulator_put() on exit ?
Also, I am missing error handling in the probe function; if something else fails,
the regulator is neither disabled nor released.

Guenter

> +		}
> +	}
> +	if (is_enable) {
> +		ret = regulator_enable(data->lm90_reg);
> +		msleep(POWER_ON_DELAY);
> +	} else {
> +		ret = regulator_disable(data->lm90_reg);
> +	}
> +
> +	if (ret < 0)
> +		dev_err(&client->dev,
> +			"Error in %s rail vdd, error %d\n",
> +			(is_enable) ? "enabling" : "disabling", ret);
> +	else
> +		dev_info(&client->dev, "success in %s rail vdd\n",
> +			 (is_enable) ? "enabling" : "disabling");
> +
> +	mutex_unlock(&data->update_lock);
> +
> +	return ret;
> +}
> +
>   static int lm90_probe(struct i2c_client *client,
>   		      const struct i2c_device_id *id)
>   {
> @@ -1406,6 +1453,10 @@ static int lm90_probe(struct i2c_client *client,
>   	i2c_set_clientdata(client, data);
>   	mutex_init(&data->update_lock);
>
> +	err = lm90_power_control(client, true);
> +	if (err < 0)
> +		return err;
> +
>   	/* Set the device type */
>   	data->kind = id->driver_data;
>   	if (data->kind == adm1032) {
> @@ -1483,6 +1534,7 @@ static int lm90_remove(struct i2c_client *client)
>   	hwmon_device_unregister(data->hwmon_dev);
>   	lm90_remove_files(client, data);
>   	lm90_restore_conf(client, data);
> +	lm90_power_control(client, false);
>
>   	return 0;
>   }
>

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