Re: [PATCH 1/4] i2c: designware-platdrv: Fix runtime PM initialization

[Jarkko Nikula]

Hi

On 04/21/2016 06:08 AM, Jisheng Zhang wrote:
> Dear Jarkko,
>
> On Wed, 20 Apr 2016 16:53:08 +0300 Jarkko Nikula wrote:
>
> > On 04/14/2016 03:53 PM, Jisheng Zhang wrote:
> > > When pm_runtime_enable() was being called, the device's usage counter
> > > was 0, causing the PM layer to runtime-suspend the device.  We then
> > > went on to call i2c_dw_probe() on a suspended device, which could hung.
> > >
> > > Fix this by incrementing the usage counter before pm_runtime_enable().
> > >
> > > Signed-off-by: Jisheng Zhang <jszhang@xxxxxxxxxxx>
> > > ---
> > >    drivers/i2c/busses/i2c-designware-platdrv.c | 14 +++++++++++++-
> > >    1 file changed, 13 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/i2c/busses/i2c-designware-platdrv.c b/drivers/i2c/busses/i2c-designware-platdrv.c
> > > index d656657..00f9e99 100644
> > > --- a/drivers/i2c/busses/i2c-designware-platdrv.c
> > > +++ b/drivers/i2c/busses/i2c-designware-platdrv.c
> > > @@ -246,6 +246,7 @@ static int dw_i2c_plat_probe(struct platform_device *pdev)
> > >    	if (dev->pm_runtime_disabled) {
> > >    		pm_runtime_forbid(&pdev->dev);
> > >    	} else {
> > > +		pm_runtime_get_noresume(&pdev->dev);
> > >    		pm_runtime_set_autosuspend_delay(&pdev->dev, 1000);
> > >    		pm_runtime_use_autosuspend(&pdev->dev);
> > >    		pm_runtime_set_active(&pdev->dev);
> >
> > pm_runtime_enable() here after pm_runtime_set_active() shouldn't suspend
> > as far as I understand which made me thinking if there is some other
>
> FWICT, on arm DT platform, the device usage counter is zero at the beginning,
> once we enable rpm, the i2c have chance to runtime suspend.
Yes it is same also for ACPI platforms. What I like to understand what 
is actually causing the runtime suspend in your case.

If I add delay longer than 1 second between pm_runtime_enable() and 
i2c_dw_probe() suspends still happens only after probe finishes. It will 
be triggered by the drivers/base/dd.c: driver_probe_device() when code 
calls the pm_request_idle().

I'm wondering is it possible there is a race with deferred probe etc. 
that is causing the issue you are seeing.

--
Jarkko