Re: [PATCH v6 3/3] eeprom: at24: enable runtime pm support

[Tomasz Figa]

On Wed, Sep 20, 2017 at 5:45 PM, sakari.ailus@xxxxxx
<sakari.ailus@xxxxxx> wrote:
> Hi Tomasz,
>
> On Wed, Sep 20, 2017 at 12:56:09PM +0900, Tomasz Figa wrote:
>> Thanks Raj.
>>
>> Let me post my comments inline.
>>
>> On Wed, Sep 20, 2017 at 12:52 PM, Mani, Rajmohan
>> <rajmohan.mani@xxxxxxxxx> wrote:
>> > Adding Tomasz...
>> >
>> >> -----Original Message-----
>> >> From: Mohandass, Divagar
>> >> Sent: Monday, September 04, 2017 3:29 AM
>> >> To: robh+dt@xxxxxxxxxx; mark.rutland@xxxxxxx; wsa@xxxxxxxxxxxxx;
>> >> sakari.ailus@xxxxxx
>> >> Cc: devicetree@xxxxxxxxxxxxxxx; linux-i2c@xxxxxxxxxxxxxxx; linux-
>> >> kernel@xxxxxxxxxxxxxxx; Mani, Rajmohan <rajmohan.mani@xxxxxxxxx>;
>> >> Mohandass, Divagar <divagar.mohandass@xxxxxxxxx>
>> >> Subject: [PATCH v6 3/3] eeprom: at24: enable runtime pm support
>> >>
>> >> 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@xxxxxxxxx>
>> >> ---
>> >>  drivers/misc/eeprom/at24.c | 38
>> >> ++++++++++++++++++++++++++++++++++++++
>> >>  1 file changed, 38 insertions(+)
>> >>
>> >> diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c index
>> >> 2199c42..d718a7a 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;
>> >> +     }
>> >> +
>> >>       /*
>> >>        * Read data from chip, protecting against concurrent updates
>> >>        * from this host, but not from other I2C masters.
>> >> @@ -518,6 +529,7 @@ static int at24_read(void *priv, unsigned int off, void
>> >> *val, size_t count)
>> >>               status = at24->read_func(at24, buf, off, count);
>> >>               if (status < 0) {
>> >>                       mutex_unlock(&at24->lock);
>> >> +                     pm_runtime_put(&client->dev);
>> >>                       return status;
>> >>               }
>> >>               buf += status;
>> >> @@ -527,17 +539,29 @@ 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.
>> >> @@ -550,6 +574,7 @@ static int at24_write(void *priv, unsigned int off, void
>> >> *val, size_t count)
>> >>               status = at24->write_func(at24, buf, off, count);
>> >>               if (status < 0) {
>> >>                       mutex_unlock(&at24->lock);
>> >> +                     pm_runtime_put(&client->dev);
>> >>                       return status;
>> >>               }
>> >>               buf += status;
>> >> @@ -559,6 +584,8 @@ 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;
>> >>  }
>> >>
>> >> @@ -743,11 +770,17 @@ static int at24_probe(struct i2c_client *client, const
>> >> struct i2c_device_id *id)
>> >>
>> >>       i2c_set_clientdata(client, at24);
>> >>
>> >> +     /* enable runtime pm */
>> >> +     pm_runtime_get_noresume(&client->dev);
>> >> +     pm_runtime_set_active(&client->dev);
>> >> +     pm_runtime_enable(&client->dev);
>>
>> Do we need this get_noresume/set_active dance? I remember it was for
>> some reason needed for PCI devices, but I don't see why for I2C
>> anything else than just pm_runtime_enable() would be necessary.
>
> You specifically do not need (all) this for PCI devices, but AFAIU for Iæ
> devices you do. The runtime PM status of a device is disabled by default
> and the use count is zero, but on ACPI based systems the device is still
> powered on.

Okay, so _get_noresume() and _set_active() would do the thing for ACPI
indeed, but not sure about other platforms. Perhaps _enable(),
_get_sync() would be more general?

Bets regards,
Tomasz