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

[Mohandass, Divagar]

Hi Sakari & Tomas,

Are you ok with the current revision, let me know if any changes are needed.

---
^Divagar

>-----Original Message-----
>From: sakari.ailus@xxxxxx [mailto:sakari.ailus@xxxxxx]
>Sent: Wednesday, September 20, 2017 3:02 PM
>To: Tomasz Figa <tfiga@xxxxxxxxxxxx>
>Cc: Mani, Rajmohan <rajmohan.mani@xxxxxxxxx>; Mohandass, Divagar
><divagar.mohandass@xxxxxxxxx>; robh+dt@xxxxxxxxxx;
>mark.rutland@xxxxxxx; wsa@xxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx;
>linux-i2c@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
>mika.westerberg@xxxxxxxxxxxxxxx
>Subject: Re: [PATCH v6 3/3] eeprom: at24: enable runtime pm support
>
>Hi Tomasz,
>
>On Wed, Sep 20, 2017 at 05:59:18PM +0900, Tomasz Figa wrote:
>> 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@the-
>dreams.de;
>> >> >> 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?
>
>What I ended up doing in e.g. the smiapp driver was to explicitly power the
>device on first and then enable runtime PM. (See
>drivers/media/i2c/smiapp/smiapp-core.c .) This approach works even if
>CONFIG_PM is disabled, both on DT and ACPI.
>
>--
>Regards,
>
>Sakari Ailus
>e-mail: sakari.ailus@xxxxxx