Re: [PATCH v3] i2c: enable runtime PM for I2C adapter devices enumerated from ACPI

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

On Monday, September 30, 2013 05:43:48 PM Mika Westerberg wrote:
> The ACPI specification requires the parent device to be powered on before
> any of its children. It can be only powered off when all the children are
> already off.
> 
> Currently whenever there is no I2C traffic going on, the I2C controller
> driver can put the device into low power state transparently to its
> children (the I2C client devices). This violates the ACPI specification
> because now the parent device is in lower power state than its children.
> 
> In order to keep ACPI happy we enable runtime PM for the I2C adapter device
> if we find out that the I2C controller was in fact an ACPI device. In
> addition to that we attach the I2C client devices to the ACPI power domain
> and make sure that they are powered on when the driver ->probe() is called.
> 
> Non-ACPI devices are not affected by this change.
> 
> This patch is based on the work by Aaron Lu and Lv Zheng.
> 
> Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> ---
>  drivers/i2c/i2c-core.c | 47 ++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 46 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
> index 29d3f04..fa861ad 100644
> --- a/drivers/i2c/i2c-core.c
> +++ b/drivers/i2c/i2c-core.c
> @@ -236,6 +236,27 @@ int i2c_recover_bus(struct i2c_adapter *adap)
>  	return adap->bus_recovery_info->recover_bus(adap);
>  }
>  
> +static void acpi_i2c_device_pm_get(struct i2c_client *client)
> +{
> +	struct i2c_adapter *adap = client->adapter;
> +
> +	/* Make sure the adapter is active */
> +	if (ACPI_HANDLE(adap->dev.parent))
> +		pm_runtime_get_sync(&adap->dev);
> +	if (ACPI_HANDLE(&client->dev))
> +		acpi_dev_pm_attach(&client->dev, true);

It would be sufficient to do

	if (ACPI_HANDLE(&client->dev)) {
		pm_runtime_get_sync(&adap->dev);
		acpi_dev_pm_attach(&client->dev, true);
	}

here (and below), because I don't think the client with an ACPI handle and the
parent without one is extremely unlikely (to the point of non-existence
actually ;-)).  And even if something like that happens, then we only enable
runtime PM for the adapter if the parent has an ACPI handle, so it still should
be OK.

Apart from this the patch looks good to me.

> +}
> +
> +static void acpi_i2c_device_pm_put(struct i2c_client *client, bool detach)
> +{
> +	struct i2c_adapter *adap = client->adapter;
> +
> +	if (ACPI_HANDLE(&client->dev) && detach)
> +		acpi_dev_pm_detach(&client->dev, true);
> +	if (ACPI_HANDLE(adap->dev.parent))
> +		pm_runtime_put(&adap->dev);
> +}
> +
>  static int i2c_device_probe(struct device *dev)
>  {
>  	struct i2c_client	*client = i2c_verify_client(dev);
> @@ -254,11 +275,15 @@ static int i2c_device_probe(struct device *dev)
>  					client->flags & I2C_CLIENT_WAKE);
>  	dev_dbg(dev, "probe\n");
>  
> +	acpi_i2c_device_pm_get(client);
> +
>  	status = driver->probe(client, i2c_match_id(driver->id_table, client));
>  	if (status) {
>  		client->driver = NULL;
>  		i2c_set_clientdata(client, NULL);
>  	}
> +
> +	acpi_i2c_device_pm_put(client, !!status);
>  	return status;
>  }
>  
> @@ -271,6 +296,8 @@ static int i2c_device_remove(struct device *dev)
>  	if (!client || !dev->driver)
>  		return 0;
>  
> +	acpi_i2c_device_pm_get(client);
> +
>  	driver = to_i2c_driver(dev->driver);
>  	if (driver->remove) {
>  		dev_dbg(dev, "remove\n");
> @@ -283,6 +310,8 @@ static int i2c_device_remove(struct device *dev)
>  		client->driver = NULL;
>  		i2c_set_clientdata(client, NULL);
>  	}
> +
> +	acpi_i2c_device_pm_put(client, true);
>  	return status;
>  }
>  
> @@ -294,8 +323,11 @@ 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) {
> +		acpi_i2c_device_pm_get(client);
>  		driver->shutdown(client);
> +		acpi_i2c_device_pm_put(client, false);
> +	}
>  }
>  
>  #ifdef CONFIG_PM_SLEEP
> @@ -1263,6 +1295,16 @@ exit_recovery:
>  	bus_for_each_drv(&i2c_bus_type, NULL, adap, __process_new_adapter);
>  	mutex_unlock(&core_lock);
>  
> +	/*
> +	 * For ACPI enumerated controllers we must make sure that the
> +	 * controller is powered on before its children. Runtime PM handles
> +	 * this for us once we have enabled it for the adapter device.
> +	 */
> +	if (ACPI_HANDLE(adap->dev.parent)) {
> +		pm_runtime_no_callbacks(&adap->dev);
> +		pm_runtime_enable(&adap->dev);
> +	}
> +
>  	return 0;
>  
>  out_list:
> @@ -1427,6 +1469,9 @@ void i2c_del_adapter(struct i2c_adapter *adap)
>  		return;
>  	}
>  
> +	if (ACPI_HANDLE(adap->dev.parent))
> +		pm_runtime_disable(&adap->dev);
> +
>  	/* Tell drivers about this removal */
>  	mutex_lock(&core_lock);
>  	bus_for_each_drv(&i2c_bus_type, NULL, adap,
> 

Thanks!

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.