Re: sl811h_suspend() and PM_EVENT_PRETHAW state handling

From: Shuah Khan
Date: Tue Aug 06 2013 - 16:37:20 EST

On 08/06/2013 12:39 PM, Alan Stern wrote:
> On Tue, 6 Aug 2013, Shuah Khan wrote:
>> sl811h_suspend() seems to be the odd routine in the way it handles the
>> PM_EVENT_PRETHAW state. It treats it same as PM_EVENT_SUSPEND and
>> PM_EVENT_HIBERNATE. All other uses I could find treat it same as
>> Reference: Commit 185849991d592497e43bcd264c6152af1261ffe2 introduced
>> PM_EVENT_PRETHAW state to sl811h_suspend().
>> Couple of questions?
>> - Why does sl811h_suspend() treat PM_EVENT_PRETHAW different from
> Because with FREEZE, the driver wants to retain the current bus state.
> With PRETHAW, it doesn't care about retaining the bus state.
> At least, that's how it looks to me. The original author of this
> driver died a couple of years ago. I don't know if anyone is using it
> any more.
>> There is no problem with this code as such, since state is passed in.
>> However, this usage conflicts with the rest of the usages and the way
>> pm_op() routine maps PM_EVENT_PRETHAW/PM_EVENT_QUIESCE to freeze() pm_ops.
>> return ops->freeze;
>> Assuming the handling PM_EVENT_PRETHAW is correct in this routine, what
>> would be the right mapping for this legacy handling to dev_pm_ops?
> It depends on the driver; there is no one answer.
> Alan Stern

With the dev_pm_ops model, drivers have to provide interfaces for each
one of these states. In this case, there will be a conflict since
pm_op() treats this state as freeze where as the driver wants to do
treat it as a suspend/hibernate. In the case of legacy pm_ops, state is
passed in as a parameter and driver could take special action if need
be, based on the state, however in dev_pm_ops model, state is not passed
in. Instead it is handled with state specific pm_ops interfaces.

For example, if this driver were to be converted to dev_pm_ops, it would
require a freeze interface which will call sl811h_bus_suspend(). Once
that is done, PM_EVENT_PRETHAW will be mapped to freeze() ops and
sl811h_bus_suspend() will be called instead of port_power(sl811, 0);

What I am getting at is, there is no provision to handle the special
case for PM_EVENT_PRETHAW like in the case of this driver when using

-- Shuah

Shuah Khan, Linux Kernel Developer - Open Source Group Samsung Research
America (Silicon Valley) | (970) 672-0658
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