Re: [PATCH] i2c: OMAP: fix static suspend vs. runtime suspend

From: Rajendra Nayak <rnayak@ti.com>
To: Kevin Hilman <khilman@ti.com>, Ben Dooks <ben-linux@fluff.org>,
	linux-i2c@vger.kernel.org
Cc: linux-pm@lists.linux-foundation.org, linux-omap@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] i2c: OMAP: fix static suspend vs. runtime suspend
Date: Mon, 31 Jan 2011 16:58:02 +0530	[thread overview]
Message-ID: <1a4ad626f3cb73267847e8ac7bd47545__28768.5112831698$1296473771$gmane$org@mail.gmail.com> (raw)
In-Reply-To: <1296173921-4832-1-git-send-email-khilman@ti.com>

Hi Kevin,

> -----Original Message-----
> From: Kevin Hilman [mailto:khilman@ti.com]
> Sent: Friday, January 28, 2011 5:49 AM
> To: Ben Dooks; Rajendra Nayak; linux-i2c@vger.kernel.org
> Cc: linux-omap@vger.kernel.org; linux-pm@lists.linux-foundation.org;
linux-arm-kernel@lists.infradead.org
> Subject: [PATCH] i2c: OMAP: fix static suspend vs. runtime suspend
>
> When runtime PM is enabled, each OMAP i2c device is suspended after
> each i2c xfer.  However, there are two cases when the static suspend
> methods must be used to ensure the devices are suspended:
>
> 1) runtime PM is disabled, either at compile time or dynamically
>     via /sys/devices/.../power/control.
> 2) an i2c client driver uses i2c during it's suspend callback, thus
>    leaving the i2c driver active (NOTE: runtime suspend transitions are
>    disabled during system suspend, so i2c activity during system
>    suspend will runtime resume the device, but not runtime (re)suspend
it.)
>
> Since the actual work to suspend the device is handled by the
> subsytem, call the bus methods to take care of it.

The patch looks good to me. Thanks for the fix.
Validated suspend on OMAP4sdp with the patch.
Can you elaborate a bit more on how/why runtime PM transitions
are disabled during system suspend, and how is it taken care
of that a runtime resume of a device works however a subsequent
runtime (re)suspend does not?

Regards,
Rajendra

>
> NOTE: This takes care of a known suspend problem on OMAP3 where the
> TWL RTC driver does i2c xfers during its suspend path leaving the i2c
> driver in an active state (since runtime suspend transistions are
> disabled.)
>
> Signed-off-by: Kevin Hilman <khilman@ti.com>
> ---
> Ben, this is a regression in 2.6.38 so hopefully this can be queued
> in the 2.6.38-rc cycle.  Thanks.
>
>  drivers/i2c/busses/i2c-omap.c |   28 ++++++++++++++++++++++++++++
>  1 files changed, 28 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-omap.c
b/drivers/i2c/busses/i2c-omap.c
> index b605ff3..0541df9 100644
> --- a/drivers/i2c/busses/i2c-omap.c
> +++ b/drivers/i2c/busses/i2c-omap.c
> @@ -1137,12 +1137,40 @@ omap_i2c_remove(struct platform_device *pdev)
>  	return 0;
>  }
>
> +#ifdef CONFIG_SUSPEND
> +static int omap_i2c_suspend(struct device *dev)
> +{
> +	if (!pm_runtime_suspended(dev))
> +		if (dev->bus && dev->bus->pm &&
dev->bus->pm->runtime_suspend)
> +			dev->bus->pm->runtime_suspend(dev);
> +
> +	return 0;
> +}
> +
> +static int omap_i2c_resume(struct device *dev)
> +{
> +	if (!pm_runtime_suspended(dev))
> +		if (dev->bus && dev->bus->pm &&
dev->bus->pm->runtime_resume)
> +			dev->bus->pm->runtime_resume(dev);
> +
> +	return 0;
> +}
> +
> +static struct dev_pm_ops omap_i2c_pm_ops = {
> +	.suspend = omap_i2c_suspend,
> +	.resume = omap_i2c_resume,
> +};
> +#else
> +#define omap_i2c_pm_ops NULL
> +#endif
> +
>  static struct platform_driver omap_i2c_driver = {
>  	.probe		= omap_i2c_probe,
>  	.remove		= omap_i2c_remove,
>  	.driver		= {
>  		.name	= "omap_i2c",
>  		.owner	= THIS_MODULE,
> +		.pm     = &omap_i2c_pm_ops,
>  	},
>  };
>
> --
> 1.7.3.5