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

Hi Sakari & Tomas,

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

---
^Divagar

-----Original Message-----
From: sakari.ailus@iki.fi [mailto:sakari.ailus@iki.fi]
Sent: Wednesday, September 20, 2017 3:02 PM
To: Tomasz Figa <tfiga@chromium.org>
Cc: Mani, Rajmohan <redacted>; Mohandass, Divagar
[off-list ref]; robh+dt@kernel.org;
mark.rutland@arm.com; wsa@the-dreams.de; devicetree@vger.kernel.org;
linux-i2c@vger.kernel.org; linux-kernel@vger.kernel.org;
mika.westerberg@linux.intel.com
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:

quoted

On Wed, Sep 20, 2017 at 5:45 PM, sakari.ailus@iki.fi
[off-list ref] wrote:

quoted

Hi Tomasz,

On Wed, Sep 20, 2017 at 12:56:09PM +0900, Tomasz Figa wrote:

quoted

Thanks Raj.

Let me post my comments inline.

On Wed, Sep 20, 2017 at 12:52 PM, Mani, Rajmohan
[off-list ref] wrote:

quoted

Adding Tomasz...

quoted

-----Original Message-----
From: Mohandass, Divagar
Sent: Monday, September 04, 2017 3:29 AM
To: robh+dt@kernel.org; mark.rutland@arm.com; wsa@the-

dreams.de;

quoted

quoted

quoted

quoted

quoted

sakari.ailus@iki.fi
Cc: devicetree@vger.kernel.org; linux-i2c@vger.kernel.org;
linux- kernel@vger.kernel.org; Mani, Rajmohan
[off-list ref]; Mohandass, Divagar
[off-list ref]
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.

quoted

quoted

quoted

quoted

quoted

Signed-off-by: Divagar Mohandass <redacted>
---
 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)  {

quoted

quoted

quoted

quoted

quoted

      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)  {

quoted

quoted

quoted

quoted

quoted

      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 I涎
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@iki.fi