linux-kernel - Re: pm runtime and system suspend resume

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Date:	Tue, 19 Jun 2012 10:48:22 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	chao xie <xiechao.linux@...il.com>
cc:	linux-pm@...r.kernel.org, <linux-kernel@...r.kernel.org>,
	<rjw@...k.pl>, <pavel@....cz>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: pm runtime and system suspend resume

On Tue, 19 Jun 2012, chao xie wrote:

> hi
> PM_RUNTIME provide a way for device driver do runtime PM. so for some
> devices, they have some surrounded logic. For example, the device may
> get clock from outside, or it need PHY support(USB is a example).
> To get these dependency out of device driver, i define a struct
> dev_pm_domain, and make dev.pm_domain point to it. So in the device
> driver, when the hardware should be enabled, we can call
> pm_runtime_get_sync while when the hardware is idle or does not work,
> we can call pm_runtime_put_sync.
> It seems work well, but i have question about the suspend/resume of
> device. When the whole system will go to deep idle, and it will
> suspend the devices. for the function do device suspend
> __device_suspend,

What source file is that function in?

>  it will call pm_runtime_get_noresume(dev). As i
> think it will make the device not do runtime suspend any more. Is that
> correct?

It sounds wrong.  Why would a suspend routine do that?

> There is the question, how device driver handle the logic surrounds
> it? I want to add pm_runtime_put_sync in dev->driver->pm->suspend
> function, and pm_runtime_get_sync in dev->driver->pm->resume.

You must not do that.  If you do, your driver will hang.

> Because
> __device_suspend increase the usage_count, pm_runtime_put_sync will
> not do real work.
> So is that right that i directly call pm_runtime_suspend in
> dev->driver->pm->suspend and pm_runtime_resume in
> dev->driver->pm->resume?

No, it works the other way around.  pm_runtime_suspend calls 
dev->driver->pm->suspend, and pm_runtime_resume calls 
dev->driver->pm->resume.

Alan Stern

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