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Date: Wed, 20 Sep 2017 11:45:20 +0300
From: "sakari.ailus@....fi" <sakari.ailus@....fi>
To: Tomasz Figa <tfiga@...omium.org>
Cc: "Mani, Rajmohan" <rajmohan.mani@...el.com>,
"Mohandass, Divagar" <divagar.mohandass@...el.com>,
"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>,
mika.westerberg@...ux.intel.com
Subject: Re: [PATCH v6 3/3] eeprom: at24: enable runtime pm support
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@...el.com> wrote:
> > Adding Tomasz...
> >
> >> -----Original Message-----
> >> From: Mohandass, Divagar
> >> Sent: Monday, September 04, 2017 3:29 AM
> >> To: robh+dt@...nel.org; mark.rutland@....com; wsa@...-dreams.de;
> >> sakari.ailus@....fi
> >> Cc: devicetree@...r.kernel.org; linux-i2c@...r.kernel.org; linux-
> >> kernel@...r.kernel.org; Mani, Rajmohan <rajmohan.mani@...el.com>;
> >> Mohandass, Divagar <divagar.mohandass@...el.com>
> >> 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@...el.com>
> >> ---
> >> 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 I²C
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.
>
> Also, we enable runtime PM, but we don't provide any callbacks. If
> there is no callback in any level of the hierarchy, NULL would be
> returned in [3], making [2] return -ENOSYS and [1] fail. The behavior
> depends on subsystem and whether the device is attached to a
> pm_domain. In our particular case I'd guess the device would be in an
> ACPI pm_domain and that would work, but the driver is generic and must
> work in any cases.
Agreed.
Cc Mika, too.
--
Regards,
Sakari Ailus
e-mail: sakari.ailus@....fi
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