External devices

[AYAN KUMAR HALDER]

> 1. Are external devices can be integrated into the runtime
> suspend/resume , or are they outside the subject of PM ? for example I
> have external dsp connected to omap, can it be integrated to the PM ?
> If it is controled through character device how can it be tailored
> into the generic PM ?

Any external device can be integrated in runtime-pm framework provided
its device driver or subsystem driver has runtime pm operations
(namely dev_pm_ops->.runtime_suspend/resume/idle).

Runtime suspend/resume is called by your driver to suspend the
respective device. It can do so by incrementing/decrementing the usage
count via pm_runtime_get and pm_runtime_put or by directly calling
pm_runtime_suspend/pm_request_resume.
So your char device driver for omap has to enable runtime pm for the
device by calling pm_runtime_set_active() and pm_runtime_enable() from
its init/probe methods.
Whenever the driver needs to wakeup the device(say on receiving a
interrupt), it can call runtime_pm_get. After handling the interrupt,
if the driver wants to suspend the device, it can call runtime_pm_put.

My statements are generic as I am unaware how the dsp functions.

> 2. When the system moves to idle does it then automatically call all
> tuntime suspend of all devices ?
>
As I have mentioned in my previous reply that the runtime-pm is device
specific(and not system specific). so each device driver calls its
runtime suspend/resume for its corresponding devices whenever it feels
so. The runtime-pm framework has some policies like it checks if the
device to be suspended has any active children or not, etc

System moving to idle state would correspond to most devices in  a
runtime-pm idle state. Each device enter into idle state when its
corresponding driver invokes so. Each device is independently moved to
idle/suspend/resume state unless their exist a parent-child
relationship between the devices.

Runtime power management is different from system power management (ie
suspend to RAM/Disk) in which the PM framework calls the suspend and
resume of all the devices(sequentially). However, these suspend/resume
functions are different from runtime suspend/resume functions.
eg
static const struct dev_pm_ops usb_device_pm_ops = {
        .prepare =      usb_dev_prepare,
        .complete =     usb_dev_complete,

/* the following two functions are system power management's
suspend/resume functions which are invoked by PM framework when the
system suspends/hibernates.  */

        .suspend =      usb_dev_suspend,
        .resume =       usb_dev_resume,
        .freeze =       usb_dev_freeze,
        .thaw =         usb_dev_thaw,
        .poweroff =     usb_dev_poweroff,
        .restore =      usb_dev_restore,
#ifdef CONFIG_USB_SUSPEND
/* the following three functions are runtime power management's
suspend/resume/idle functions invoked by the driver when it wants to
put the corresponding device in suspend/idle/resume state.  */
        .runtime_suspend =      usb_runtime_suspend,
        .runtime_resume =       usb_runtime_resume,
        .runtime_idle =         usb_runtime_idle,
#endif
};

Regards,
Ayan Kumar Halder