linux-kernel - Re: [RFC v2 1/5] PM, Runtime, Add power_must_be

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Date:	Sat, 5 May 2012 13:59:07 +0800
From:	huang ying <huang.ying.caritas@...il.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	Huang Ying <ying.huang@...el.com>, ming.m.lin@...el.com,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Zheng Yan <zheng.z.yan@...el.com>
Subject: Re: [RFC v2 1/5] PM, Runtime, Add power_must_be_on flag

On Sat, May 5, 2012 at 3:50 AM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
> On Fri, May 4, 2012 at 2:13 AM, Huang Ying <ying.huang@...el.com> wrote:
>> --- a/include/linux/pm.h
>> +++ b/include/linux/pm.h
>> @@ -536,6 +536,7 @@ struct dev_pm_info {
>>        unsigned int            irq_safe:1;
>>        unsigned int            use_autosuspend:1;
>>        unsigned int            timer_autosuspends:1;
>> +       unsigned int            power_must_be_on:1;
>>        enum rpm_request        request;
>>        enum rpm_status         runtime_status;
>>        int                     runtime_error;
>
> It's a little weird to just add the field, with no users.  Would it
> make sense to pull out the bits of patch 5 that use this and combine
> them into a single smaller patch?

This patch is needed by some other subsystem too, such as ZPODD
support in following patchset:

https://lkml.org/lkml/2012/3/28/23

The original plan is to merge this into linux-pm.git firstly, then
merge various usage of this flag into various subsystem git tree.
That will make cross-tree merging a little easier.  Is it possible?

> But see related comments there; it
> might be safer to have a function that computes this whenever you need
> it instead of caching the value.

This flag may be used (or calculated if implemented as a function)
when device is in suspended state.  Reason is as follow from the
changelog of this patch.

"
In general, whether to put a device into power off state should be
decided by the driver of the device, but for some buses, whether to
put a device into power off state may be done by the parent of the
device.  For example, a PCIe end point device may be put into power
off state by the PCIe port connected to it.
"

If all devices can calculate "power_must_be_on" when it is in
suspended state, then this will be a design choice.

Hi, Rafael,

What do you think about the idea to replace .power_must_be_on with a
function (maybe add a new callback in pm_ops)?

Best Regards,
Huang Ying
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