linux-kernel - Re: [PATCH v2] i2c: designware: Avoid unnecessary resuming during system suspend

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Message-ID: <20150525104206.1c9bf3bf@xhacker>
Date:	Mon, 25 May 2015 10:42:06 +0800
From:	Jisheng Zhang <jszhang@...vell.com>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
CC:	<wsa@...-dreams.de>, <linux-i2c@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<jarkko.nikula@...ux.intel.com>
Subject: Re: [PATCH v2] i2c: designware: Avoid unnecessary resuming during
 system suspend

Dear Wolfram, Mika,

On Thu, 21 May 2015 14:40:49 +0300
Mika Westerberg <mika.westerberg@...ux.intel.com> wrote:

> [Adding Jarkko, just in case he has concerns about this]
> 
> On Wed, May 20, 2015 at 10:33:13PM +0800, Jisheng Zhang wrote:
> > Commit 1fc2fe204cb9 ("i2c: designware: Add runtime PM hooks") adds
> > runtime pm support using the same ops for system pm and runtime pm.
> > When suspend to ram, the i2c host may have been runtime suspended, thus
> > i2c_dw_disable() hangs.
> > 
> > Previously, I fixed this issue by separating ops for system pm and
> > runtime pm, then in the system suspend/resume path, runtime pm apis are
> > used to ensure the device is at correct state.
> > 
> > But as Mika Westerberg pointed out: it sounds a bit silly to resume the
> > device just because you want to call i2c_dw_disable() for it before
> > suspending again. He then suggested an elegant solution which keeps the
> > device runtime suspended during system suspend with the help of
> > 'dev->power.direct_complete'. This patch adopted this solution, and in
> > fact Mika provided the main code.
> > 
> > Signed-off-by: Jisheng Zhang <jszhang@...vell.com>
> > ---
> >  v2 change:
> > 	- adopt Mika's suggestion to make use of direct_complete flag
> > 
> >  drivers/i2c/busses/i2c-designware-platdrv.c | 33 +++++++++++++++++++++++++----
> >  1 file changed, 29 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/i2c/busses/i2c-designware-platdrv.c b/drivers/i2c/busses/i2c-designware-platdrv.c
> > index 0a80e4a..f89650f 100644
> > --- a/drivers/i2c/busses/i2c-designware-platdrv.c
> > +++ b/drivers/i2c/busses/i2c-designware-platdrv.c
> > @@ -298,6 +298,22 @@ static const struct of_device_id dw_i2c_of_match[] = {
> >  MODULE_DEVICE_TABLE(of, dw_i2c_of_match);
> >  #endif
> >  
> > +#ifdef CONFIG_PM_SLEEP
> > +static int dw_i2c_prepare(struct device *dev)
> > +{
> > +	return pm_runtime_suspended(dev);
> > +}
> > +
> > +static void dw_i2c_complete(struct device *dev)
> > +{
> > +	if (dev->power.direct_complete)
> > +		pm_request_resume(dev);
> > +}
> > +#else
> > +#define dw_i2c_prepare	NULL
> > +#define dw_i2c_complete	NULL
> > +#endif
> > +
> >  #ifdef CONFIG_PM
> >  static int dw_i2c_suspend(struct device *dev)
> >  {
> > @@ -322,10 +338,19 @@ static int dw_i2c_resume(struct device *dev)
> >  
> >  	return 0;
> >  }
> > -#endif
> >  
> > -static UNIVERSAL_DEV_PM_OPS(dw_i2c_dev_pm_ops, dw_i2c_suspend,
> > -			    dw_i2c_resume, NULL);
> > +static const struct dev_pm_ops dw_i2c_dev_pm_ops = {
> > +	.prepare = dw_i2c_prepare,
> > +	.complete = dw_i2c_complete,
> > +	SET_SYSTEM_SLEEP_PM_OPS(dw_i2c_suspend, dw_i2c_resume)
> > +	SET_RUNTIME_PM_OPS(dw_i2c_suspend,
> > +		dw_i2c_resume, NULL)
> 
> No need to wrap here. It will fit into 80 chars limit.

OOPs, yes. Do I need to send a new version?

> 
> Otherwise looks good to me. I also tested this on Braswell and Skylake
> machines where it didn't cause any problems,
> 
> Acked-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> Tested-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> 

Thanks for these.
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