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

From: [email-masked] (Lina Iyer)
Date: Mon, 24 Oct 2016 10:16:05 -0600

On Sat, Oct 22 2016 at 18:19 -0600, Rafael J. Wysocki wrote:
>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 <[email-masked]>
>> Acked-by: Ulf Hansson <[email-masked]>
>> ---
>> 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. 
>
This is correct. But the last line may need a bit of modification. If
all devices in a PM domain are IRQ-safe and the domain is NOT, then it
it is a valid combination just that the domain would never do runtime
PM.

> 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?
>
Yes, this precisely reflects the code.

Thanks,
Lina