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

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Date:   Tue, 10 Oct 2017 12:55:45 +0900
From:   Tomasz Figa <tfiga@...omium.org>
To:     "Mohandass, Divagar" <divagar.mohandass@...el.com>
Cc:     "sakari.ailus@....fi" <sakari.ailus@....fi>,
        "Mani, Rajmohan" <rajmohan.mani@...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" <mika.westerberg@...ux.intel.com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v6 3/3] eeprom: at24: enable runtime pm support

On Mon, Oct 9, 2017 at 12:14 PM, Mohandass, Divagar
<divagar.mohandass@...el.com> wrote:
> Hi Tomasz,
>
>>-----Original Message-----
>>From: sakari.ailus@....fi [mailto:sakari.ailus@....fi]
>>Sent: Tuesday, October 03, 2017 7:21 PM
>>To: Tomasz Figa <tfiga@...omium.org>
>>Cc: Mani, Rajmohan <rajmohan.mani@...el.com>; Mohandass, Divagar
>><divagar.mohandass@...el.com>; robh+dt@...nel.org;
>>mark.rutland@....com; wsa@...-dreams.de; devicetree@...r.kernel.org;
>>linux-i2c@...r.kernel.org; linux-kernel@...r.kernel.org;
>>mika.westerberg@...ux.intel.com; linux-pm@...r.kernel.org
>>Subject: Re: [PATCH v6 3/3] eeprom: at24: enable runtime pm support
>>
>>Hi Tomasz,
>>
>>On Wed, Sep 20, 2017 at 12:32:22PM +0300, sakari.ailus@....fi wrote:
>>> > >> >> @@ -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.
>>
>>pm_runtime_get_noresume() + pm_runtime_put() can be replaced by a single
>>pm_runtime_idle() call (where pm_runtime_put() was). pm_runtime_enable()
>>is required to enable runtime PM for a device.
>
> Verified the change suggested by Sakari.
> Let me know I can send a updated patch version with this change.

Okay, looks like Sakari confirmed that the driver should work fine
without callbacks, so please go ahead. Thanks for patience.

Best regards,
Tomasz