linux-kernel - Re: [PATCH] i2c/designware: enable i2c controller to suspend/resume asynchronously

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Date:	Tue, 05 Jan 2016 14:14:16 +0200
From:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:	Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
	"Fu, Zhonghui" <zhonghui.fu@...ux.intel.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Wolfram Sang <wsa@...-dreams.de>
Cc:	linux-i2c@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	srinivas.kowtal@...el.com
Subject: Re: [PATCH] i2c/designware: enable i2c controller to suspend/resume
 asynchronously

On Tue, 2016-01-05 at 10:53 +0200, Jarkko Nikula wrote:
> Hi
> 
> On 12/24/2015 04:30 PM, Fu, Zhonghui wrote:
> > Now, PM core supports asynchronous suspend/resume mode for devices
> > during system suspend/resume, and the power state transition of one
> > device may be completed in separate kernel thread. PM core ensures
> > all power state transition dependency between devices. This patch
> > enables designware i2c controllers to suspend/resume
> > asynchronously.
> > This will take advantage of multicore and improve system
> > suspend/resume
> > speed. After enabling all i2c devices, i2c adapters and i2c
> > controllers
> > on ASUS T100TA tablet, the system suspend-to-idle time is reduced
> > to
> > about 510ms from 750ms, and the system resume time is reduced to
> > about
> > 790ms from 900ms.
> > 
> Nice reduction :-)
> 
> > diff --git a/drivers/i2c/busses/i2c-designware-platdrv.c
> > b/drivers/i2c/busses/i2c-designware-platdrv.c
> > index 6b00061..395130b 100644
> > --- a/drivers/i2c/busses/i2c-designware-platdrv.c
> > +++ b/drivers/i2c/busses/i2c-designware-platdrv.c
> > @@ -230,6 +230,7 @@ static int dw_i2c_plat_probe(struct
> > platform_device *pdev)
> >   	}
> > 
> >   	adap = &dev->adapter;
> > +	device_enable_async_suspend(&pdev->dev);
> >   	adap->owner = THIS_MODULE;
> >   	adap->class = I2C_CLASS_DEPRECATED;
> >   	ACPI_COMPANION_SET(&adap->dev, ACPI_COMPANION(&pdev-
> > >dev));
> 
> Does device_enable_async_suspend() need to be called before enabling 
> runtime PM? I suppose not since there appears to have also related
> sysfs 
> node for toggling it runtime.
> 
> I'm thinking if you could move the device_enable_async_suspend() call
> into drivers/i2c/busses/i2c-designware-core.c: i2c_dw_probe() and
> then 
> also PCI enumerated adapter could take advantage of it.

I concern about Intel BayTrail-T / Braswell / CherryTrail cases, since
we have non-trivial PM for LPSS there. Zhonghui, have you a chance to
stress test this on platforms based on mentioned SoCs?


-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy

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