[PATCH v3 [fix]] PM / doc: Update device documentation for devices in IRQ safe PM domains

[Rafael J. Wysocki]

On Friday, October 21, 2016 03:52:55 PM Lina Iyer wrote:
> Update documentation to reflect the changes made to support IRQ safe PM
> domains.
> 
> Signed-off-by: Lina Iyer <lina.iyer at linaro.org>
> Acked-by: Ulf Hansson <ulf.hansson at linaro.org>
> ---
> Changes since v3:
> - Moved para to the end of the section
> - Added clause for all IRQ safe devices in a domain
> - Cleanup explanation of nested domains
> ---
>  Documentation/power/devices.txt | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/power/devices.txt b/Documentation/power/devices.txt
> index 8ba6625..9218ce6 100644
> --- a/Documentation/power/devices.txt
> +++ b/Documentation/power/devices.txt
> @@ -607,7 +607,9 @@ individually.  Instead, a set of devices sharing a power resource can be put
>  into a low-power state together at the same time by turning off the shared
>  power resource.  Of course, they also need to be put into the full-power state
>  together, by turning the shared power resource on.  A set of devices with this
> -property is often referred to as a power domain.
> +property is often referred to as a power domain. A power domain may also be
> +nested inside another power domain. The nested domain is referred to as the
> +sub-domain of the parent domain.
>  
>  Support for power domains is provided through the pm_domain field of struct
>  device.  This field is a pointer to an object of type struct dev_pm_domain,
> @@ -629,6 +631,13 @@ support for power domains into subsystem-level callbacks, for example by
>  modifying the platform bus type.  Other platforms need not implement it or take
>  it into account in any way.
>  
> +Devices and PM domains may be defined as IRQ-safe, if they can be powered
> +on/off even when the IRQs are disabled.

What IRQ-safe means for devices is that their runtime PM callbacks may be
invoked with interrupts disabled on the local CPU.  I guess the meaning of
IRQ-safe for PM domains is analogous, but the above isn't precise enough to me.

> An IRQ-safe device in a domain will
> +disallow power management on the domain, unless the domain is also defined as
> +IRQ-safe. In other words, a domain containing all IRQ-safe devices must also
> +be defined as IRQ-safe. Another restriction this framework imposes on the
> +parent domain of an IRQ-safe domain is that the parent domain must also be
> +defined as IRQ-safe.

What about this:

"Devices may be defined as IRQ-safe which indicates to the PM core that their
runtime PM callbacks may be invoked with disabled interrupts (see
Documentation/power/runtime_pm.txt for more information).  If an IRQ-safe
device belongs to a PM domain, the runtime PM of the domain will be disallowed,
unless the domain itself is defined as IRQ-safe.  However, a PM domain can only
be defined as IRQ-safe if all of the devices in it are IRQ-safe.  Moreover, if
an IRQ-safe domain has a parent domain, the runtime PM of the parent is only
allowed if the parent itself is IRQ-safe too with the additional restriction
that all child domains of an IRQ-safe parent must also be IRQ-safe."

Does it actually reflect what the code does?

Thanks,
Rafael