linux-kernel - RE: [PATCH v2 3/3] eeprom: at24: enable runtime pm support

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Date:   Wed, 30 Aug 2017 04:05:03 +0000
From:   "Mohandass, Divagar" <divagar.mohandass@...el.com>
To:     Sakari Ailus <sakari.ailus@....fi>
CC:     "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "wsa@...-dreams.de" <wsa@...-dreams.de>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Mani, Rajmohan" <rajmohan.mani@...el.com>
Subject: RE: [PATCH v2 3/3] eeprom: at24: enable runtime pm support

Hi Sakari,

Thanks for your review comments.
My comments below.

---
^Divagar

>-----Original Message-----
>From: Sakari Ailus [mailto:sakari.ailus@....fi]
>Sent: Tuesday, August 22, 2017 2:26 PM
>To: Mohandass, Divagar <divagar.mohandass@...el.com>
>Cc: robh+dt@...nel.org; mark.rutland@....com; wsa@...-dreams.de;
>devicetree@...r.kernel.org; linux-i2c@...r.kernel.org; linux-
>kernel@...r.kernel.org; Mani, Rajmohan <rajmohan.mani@...el.com>
>Subject: Re: [PATCH v2 3/3] eeprom: at24: enable runtime pm support
>
>Hi Divagar,
>
>Thanks for the patch. Please see my comments below.
>
>On Tue, Aug 15, 2017 at 12:11:59AM +0530, Divagar Mohandass wrote:
>> Currently the device is kept in D0, there is an opportunity to save
>> power by enabling runtime pm.
>>
>> Device can be daisy chained from PMIC and we can't rely on I2C core
>> for auto resume/suspend. Driver will decide when to resume/suspend.
>>
>> Signed-off-by: Divagar Mohandass <divagar.mohandass@...el.com>
>> ---
>>  drivers/misc/eeprom/at24.c | 34 ++++++++++++++++++++++++++++++++++
>>  1 file changed, 34 insertions(+)
>>
>> diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
>> index 2199c42..0d26681 100644
>> --- a/drivers/misc/eeprom/at24.c
>> +++ b/drivers/misc/eeprom/at24.c
>> @@ -24,6 +24,7 @@
>>  #include <linux/i2c.h>
>>  #include <linux/nvmem-provider.h>
>>  #include <linux/platform_data/at24.h>
>> +#include <linux/pm_runtime.h>
>>
>>  /*
>>   * I2C EEPROMs from most vendors are inexpensive and mostly
>interchangeable.
>> @@ -501,11 +502,21 @@ static ssize_t at24_eeprom_write_i2c(struct
>> at24_data *at24, const char *buf,  static int at24_read(void *priv,
>> unsigned int off, void *val, size_t count)  {
>>  	struct at24_data *at24 = priv;
>> +	struct i2c_client *client;
>>  	char *buf = val;
>> +	int ret;
>>
>>  	if (unlikely(!count))
>>  		return count;
>>
>> +	client = at24_translate_offset(at24, &off);
>> +
>> +	ret = pm_runtime_get_sync(&client->dev);
>> +	if (ret < 0) {
>> +		pm_runtime_put_noidle(&client->dev);
>> +		return ret;
>> +	}
>> +
>
>at24_read() may fail between the two chunks here. You'll need
>pm_runtime_put() before returning the error code.

Ack

>
>>  	/*
>>  	 * Read data from chip, protecting against concurrent updates
>>  	 * from this host, but not from other I2C masters.
>> @@ -527,17 +538,29 @@ static int at24_read(void *priv, unsigned int
>> off, void *val, size_t count)
>>
>>  	mutex_unlock(&at24->lock);
>>
>> +	pm_runtime_put(&client->dev);
>> +
>>  	return 0;
>>  }
>>
>>  static int at24_write(void *priv, unsigned int off, void *val, size_t
>> count)  {
>>  	struct at24_data *at24 = priv;
>> +	struct i2c_client *client;
>>  	char *buf = val;
>> +	int ret;
>>
>>  	if (unlikely(!count))
>>  		return -EINVAL;
>>
>> +	client = at24_translate_offset(at24, &off);
>> +
>> +	ret = pm_runtime_get_sync(&client->dev);
>> +	if (ret < 0) {
>> +		pm_runtime_put_noidle(&client->dev);
>> +		return ret;
>> +	}
>> +
>>  	/*
>>  	 * Write data to chip, protecting against concurrent updates
>>  	 * from this host, but not from other I2C masters.
>
>Ditto for write.

Ack

>
>> @@ -559,6 +582,8 @@ static int at24_write(void *priv, unsigned int
>> off, void *val, size_t count)
>>
>>  	mutex_unlock(&at24->lock);
>>
>> +	pm_runtime_put(&client->dev);
>> +
>>  	return 0;
>>  }
>>
>> @@ -743,6 +768,13 @@ static int at24_probe(struct i2c_client *client,
>> const struct i2c_device_id *id)
>>
>>  	i2c_set_clientdata(client, at24);
>>
>> +	/* enable runtime pm */
>> +	err = pm_runtime_set_active(&client->dev);
>> +	if (err < 0)
>> +		goto err_clients;
>> +
>> +	pm_runtime_enable(&client->dev);
>> +
>
>Here, too: at24_read() below can fail, as well as nvmem_register().

Ack
In addition to that calling pm_runtime_get_noresume before enabling pm.

>
>>  	/*
>>  	 * Perform a one-byte test read to verify that the
>>  	 * chip is functional.
>> @@ -810,6 +842,8 @@ static int at24_remove(struct i2c_client *client)
>>  	for (i = 1; i < at24->num_addresses; i++)
>>  		i2c_unregister_device(at24->client[i]);
>>
>> +	pm_runtime_disable(&client->dev);
>
>pm_runtime_set_suspended(&client->dev)

Ack

>
>> +
>>  	return 0;
>>  }
>>
>
>--
>Regards,
>
>Sakari Ailus
>e-mail: sakari.ailus@....fi