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Message-ID: <68875641.UkNsrXLDeP@vostro.rjw.lan>
Date: Tue, 20 Aug 2013 16:16:31 +0200
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc: linux-i2c@...r.kernel.org, Wolfram Sang <wsa@...-dreams.de>,
"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
Lv Zheng <lv.zheng@...el.com>, Aaron Lu <aaron.lu@...el.com>
Subject: Re: [RFC PATCH 1/2] i2c: prepare runtime PM support for I2C client devices
On Tuesday, August 20, 2013 05:03:35 PM Mika Westerberg wrote:
> From: Aaron Lu <aaron.lu@...el.com>
>
> This patch adds runtime PM support for the I2C bus in a similar way that
> has been done for PCI bus already. This means that the I2C bus core
> prepares runtime PM for a client device just before a driver is about to be
> bound to it. Devices that are not bound to any driver are not prepared for
> runtime PM.
>
> In order to take advantage of this runtime PM support, the client device
> driver needs drop the device runtime PM reference count by calling
> pm_runtime_put() in its ->probe() callback and possibly implement rest of
> the runtime PM callbacks.
>
> However, this does not yet make runtime PM happen for the device, it has to
> be explicitly allowed from userspace per each I2C client device. The
> reason for this is that things like HID over I2C might not work as smoothly
> when runtime PM is active. So we leave it to the user to balance between
> performance and power efficiency.
>
> User can allow runtime PM for the client device by running:
>
> # echo auto > /sys/bus/i2c/devices/<device>/power/control
>
> and it can be forbidden again by:
>
> # echo on > /sys/bus/i2c/devices/<device>/power/control
>
> Status of the device can be monitored by reading files under the device
> power directory.
>
> If the driver doesn't support runtime PM (like most of the existing I2C
> client drivers), the device in question is regarded as being runtime PM
> active and powered on.
>
> The patch adds also runtime PM support for the adapter device because it is
> needed to be able to runtime power manage the I2C controller device. The
> adapter device is handled along with the I2C controller device (it uses
> pm_runtime_no_callbacks()).
>
> Signed-off-by: Aaron Lu <aaron.lu@...el.com>
> Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
> drivers/i2c/i2c-core.c | 48 +++++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 47 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
> index 3d44292..8fad5ac 100644
> --- a/drivers/i2c/i2c-core.c
> +++ b/drivers/i2c/i2c-core.c
> @@ -254,11 +254,34 @@ static int i2c_device_probe(struct device *dev)
> client->flags & I2C_CLIENT_WAKE);
> dev_dbg(dev, "probe\n");
>
> + /* Make sure the adapter is active */
> + pm_runtime_get_sync(&client->adapter->dev);
> +
> + /*
> + * Enable runtime PM for the client device. If the client wants to
> + * participate on runtime PM it should call pm_runtime_put() in its
> + * probe() callback.
> + *
> + * User still needs to allow the PM runtime before it can actually
> + * happen.
> + */
> + pm_runtime_forbid(&client->dev);
> + pm_runtime_get_noresume(&client->dev);
> + pm_runtime_set_active(&client->dev);
> + pm_runtime_enable(&client->dev);
> +
> status = driver->probe(client, i2c_match_id(driver->id_table, client));
> if (status) {
> client->driver = NULL;
> i2c_set_clientdata(client, NULL);
> +
> + pm_runtime_disable(&client->dev);
> + pm_runtime_set_suspended(&client->dev);
> + pm_runtime_put_noidle(&client->dev);
> }
> +
> + pm_runtime_put(&client->adapter->dev);
> +
> return status;
> }
>
> @@ -271,6 +294,8 @@ static int i2c_device_remove(struct device *dev)
> if (!client || !dev->driver)
> return 0;
>
> + pm_runtime_get_sync(&client->adapter->dev);
> +
> driver = to_i2c_driver(dev->driver);
> if (driver->remove) {
> dev_dbg(dev, "remove\n");
> @@ -283,6 +308,13 @@ static int i2c_device_remove(struct device *dev)
> client->driver = NULL;
> i2c_set_clientdata(client, NULL);
> }
> +
> + /* Undo the runtime PM done in i2c_probe() */
> + pm_runtime_disable(&client->dev);
> + pm_runtime_set_suspended(&client->dev);
> + pm_runtime_put_noidle(&client->dev);
> +
> + pm_runtime_put(&client->adapter->dev);
> return status;
> }
>
> @@ -294,8 +326,11 @@ static void i2c_device_shutdown(struct device *dev)
> if (!client || !dev->driver)
> return;
> driver = to_i2c_driver(dev->driver);
> - if (driver->shutdown)
> + if (driver->shutdown) {
> + pm_runtime_get_sync(&client->adapter->dev);
> driver->shutdown(client);
> + pm_runtime_put(&client->adapter->dev);
> + }
> }
>
> #ifdef CONFIG_PM_SLEEP
> @@ -1263,6 +1298,15 @@ exit_recovery:
> bus_for_each_drv(&i2c_bus_type, NULL, adap, __process_new_adapter);
> mutex_unlock(&core_lock);
>
> + /*
> + * Make sure the adapter runtime PM follows the parent device (the
> + * host controller) so that we can suspend it once there aren't any
> + * active clients anymore.
> + */
> + pm_runtime_set_active(&adap->dev);
> + pm_runtime_no_callbacks(&adap->dev);
> + pm_runtime_enable(&adap->dev);
> +
> return 0;
>
> out_list:
> @@ -1427,6 +1471,8 @@ void i2c_del_adapter(struct i2c_adapter *adap)
> return;
> }
>
> + pm_runtime_disable(&adap->dev);
> +
> /* Tell drivers about this removal */
> mutex_lock(&core_lock);
> bus_for_each_drv(&i2c_bus_type, NULL, adap,
>
--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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