linux-kernel - Re: [PATCH] i2c: designware: separate ops for system_sleep_pm and runtime

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Date:	Wed, 20 May 2015 20:05:40 +0800
From:	Jisheng Zhang <jszhang@...vell.com>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	<wsa@...-dreams.de>
CC:	<linux-i2c@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] i2c: designware: separate ops for system_sleep_pm and
 runtime_pm

Dear Mika,

On Wed, 20 May 2015 19:34:22 +0800
Jisheng Zhang <jszhang@...vell.com> wrote:

> Dear Mika,
> 
> On Tue, 19 May 2015 16:15:16 +0300
> Mika Westerberg <mika.westerberg@...ux.intel.com> wrote:
> 
> > On Tue, May 19, 2015 at 08:32:42PM +0800, Jisheng Zhang wrote:
> > > > I can see that this fixes the issue with the platform driver (as the
> > > > platform bus core doesn't power on the device automatically as opposed
> > > > to other buses, like PCI). However, I'm thinking that can we do better
> > > > here.
> > > > 
> > > > Instead of powering the device on again, can't we leave it in low power
> > > > state? Recently added 'dev->power.direct_complete' may be used to
> > > > achieve that, I think.
> > > 
> > > how to handle runtime suspended via just being clock gated?
> > 
> > As far as I can tell driver's suspend hook does the clock gating so why
> > would you need to handle it differently? Once the device is runtime
> > suspended, it is both clock and power gated depending on the platform.
> 
> Sorry for confusion. Considering one platform which doesn't support power off
> the i2c host but it can disable the host's clock. So in such platform, when
> the host is runtime suspended, its clock is disabled, then i2c_dw_disable() will
> hang when s2ram. Except using the runtime pm API to ensure the host is in
> a correct state, is there any other solution? AFAIK, 'dev->power.direct_complete'
> doesn't help such case.

I misunderstood the direct_complete flag usage. I think it can help such case
will investigate and provide new patch if necessary.

Thanks a lot
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