Subject: [PATCH] driver core / PM: Add callbacks for PM domain initialization/cleanup

From: [email-masked] (Greg Kroah-Hartman)
Date: Thu, 19 Mar 2015 14:29:07 +0100

On Wed, Mar 18, 2015 at 04:02:11PM +0100, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <[email-masked]>
> 
> If PM domains are in use, it may be necessary to prepare the code
> handling a PM domain for driver probing.  For example, in some
> cases device drivers rely on the ability to power on the devices
> with the help of the IO runtime PM framework and the PM domain
> code needs to be ready for that.  Also, if that code has not been
> fully initialized yet, the driver probing should be deferred.
> 
> Moreover, after the probing is complete, it may be necessary to
> put the PM domain in question into the state reflecting the current
> needs of the devices in it, for example, to prevent power from being
> drawn in vain.
> 
> For these reasons, introduce new PM domain callbacks, ->activate
> and ->sync, called, respectively, before probing for a device
> driver and after the probing has been completed.
> 
> That is not sufficient, however, because the device's PM domain
> pointer has to be populated for the ->activate callback to be
> executed, so setting it in bus type ->probe callback routines
> would be too late.  Also, there are bus types where PM domains
> are not used at all and the core should not attempt to set the
> pm_domain pointer for the devices on those buses.
> 
> To overcome that difficulty, introduce two new bus type
> callbacks, ->init and ->release, called by bus_add_device() and
> bus_remove_device(), respectively.  That will allow ->init to
> be used to populate the pm_domain pointer for the bus types
> that want to do that and ->release will be useful for any
> cleanup that may be necessary after removing a device that
> was part of a PM domain.
> 
> Signed-off-by: Rafael J. Wysocki <[email-masked]>
> ---
> 
> It occured to me that we might want to ->sync regardless of whether or
> not the probing had been succenssful, so I changed the code in
> really_probe() along these lines.  Please let me know if that's
> not OK.
> 
> ---
>  drivers/base/bus.c     |   12 +++++++++++-
>  drivers/base/dd.c      |   20 ++++++++++++++------
>  include/linux/device.h |    5 +++++
>  include/linux/pm.h     |    6 ++++++
>  4 files changed, 36 insertions(+), 7 deletions(-)
> 
> Index: linux-pm/drivers/base/bus.c
> ===================================================================
> --- linux-pm.orig/drivers/base/bus.c
> +++ linux-pm/drivers/base/bus.c
> @@ -509,10 +509,15 @@ int bus_add_device(struct device *dev)
>  	int error = 0;
>  
>  	if (bus) {
> +		if (bus->init) {
> +			error = bus->init(dev);
> +			if (error)
> +				goto out_put;
> +		}

This doesn't make sense to me.  A bus just called bus_add_device, it can
do whatever it wanted to right before calling this function, no need for
another callback.

>  		pr_debug("bus: '%s': add device %s\n", bus->name, dev_name(dev));
>  		error = device_add_attrs(bus, dev);
>  		if (error)
> -			goto out_put;
> +			goto out_release;
>  		error = device_add_groups(dev, bus->dev_groups);
>  		if (error)
>  			goto out_groups;
> @@ -534,6 +539,9 @@ out_groups:
>  	device_remove_groups(dev, bus->dev_groups);
>  out_id:
>  	device_remove_attrs(bus, dev);
> +out_release:
> +	if (bus->release)
> +		bus->release(dev);

>  out_put:
>  	bus_put(dev->bus);
>  	return error;
> @@ -597,6 +605,8 @@ void bus_remove_device(struct device *de
>  	device_remove_groups(dev, dev->bus->dev_groups);
>  	if (klist_node_attached(&dev->p->knode_bus))
>  		klist_del(&dev->p->knode_bus);
> +	if (bus->release)
> +		bus->release(dev);

Same with release(), this happens when a bus wants to remove a device,
it controls this, why have a callback right away?  These both shouldn't
be needed.

sorry if I missed this before, I hadn't noticed these callbacks in
previous patches but I wasn't paying much attention.

thanks,

greg k-h