Message-ID: <20110922180335.GQ17168@ponder.secretlab.ca>
Date:	Thu, 22 Sep 2011 12:03:35 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Stephen Warren <swarren@...dia.com>
Cc:	Ben Dooks <ben-linux@...ff.org>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Arnd Bergmann <arnd@...db.de>, Colin Cross <ccross@...gle.com>,
	Olof Johansson <olof@...om.net>,
	Erik Gilling <konkers@...roid.com>, linux-i2c@...r.kernel.org,
	linux-tegra@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, Dilan Lee <dilee@...dia.com>
Subject: Re: [PATCH v2] i2c-tegra: Use the suspend_noirq/resume_noirq not
 suspend/resume

On Thu, Sep 22, 2011 at 11:51:32AM -0600, Stephen Warren wrote:
> From: Dilan Lee <dilee@...dia.com>
> 
> Various drivers need to use the I2C bus during suspend. Generally, this
> is already supported, since devices are suspended based on (the inverse of)
> probe order, and an I2C-based device can't probe until the I2C bus upon
> which it sits has been probed first.
> 
> However, some subsystems, notably ASoC, do not enjoy such simple bus/child
> probing relationships. In particular, an ASoC machine driver (and hence a
> sound card) may probe very early on before all its required resources are
> available. After all required resources become available, the overall
> machine driver initialization is performed. Suspend of a sound card occurs
> based on the machine driver's probe timing, which may mean suspend occurs
> after an I2C bus has been suspended. In turn, components within the sound
> card suspend when the overall card suspends. If one of those components
> is an I2C device, this may mean the device attempts to suspend after the
> I2C bus it sits upon. Conversely, resume may occur before the I2C bus is
> available. Consequently, I2C accesses during suspend/resume will fail.
> 
> This causes the following issue:
> 
>   We found the register settings of wm8903(an audio codec) can't be modified
>   in snd_soc_suspend since I2C bus has been suspended before snd_soc_suspend.
> 
>   Pop noise will occur when system resume from LP0 if the register settings
>   of wm8903 haven't be modified correctly in snd_soc_suspend.
> 
> To solve this, the I2C bus driver is modified to use suspend_noirq and
> resume_noirq instead of suspend and resume. This delays the I2C bus suspend
> until after the ASoC card-level suspend, and everything works.
> 
> It is acknowledged that this is not an ideal solution. However, this solution
> is the best currently available within the kernel.
> 
> Suggested alternatives are:
> 
> * Implement an explicit dependency management system within the kernel for
>   device suspend/resume, such that I2C bus would not be suspended before
>   the sound card that requires it. It is reported that Linus rejected this
>   proposal since he wanted suspend ordering to be based on probe ordering.

This really should be revisted.  That was in the context of full
system suspend, but we're now in a world of runtime suspend which
absolutely does need dependency tracking or reference counting to get
the ordering right.

> * Enhance device probing such that the ASoC sound card device could defer
>   its probing until all required resources were available. This would
>   then cause the overall sound card suspend to occur at an appropriate early
>   time. Grant Likely was reported to have been working towards this goal.

Yes, I'll send you my current patch for you to look at.  One of the
engineers from Linaro is going to be pushing that patch set forward.
However, I don't know if it helps with this problem because I believe
that the suspend order is based on the implicit probe order of
devices, but my patch allows drivers to cause the probe order to get
rearranged at runtime.  I don't believe there is a global list showing
the order that devices successfully got probed, but I may be wrong
here.

g.

> 
> [swarren: Rewrote patch description to reflect upstream discussion]
> 
> Signed-off-by: Dilan Lee <dilee@...dia.com>
> Signed-off-by: Stephen Warren <swarren@...dia.com>
> Acked-by: Arnd Bergmann <arnd@...db.de>
> Reviewed-by: Mark Brown <broonie@...nsource.wolfsonmicro.com>
> ---
> v2: Summarized the email thread in patch description.
>     Added Arnd/Mark's ack/review tags
> 
>  drivers/i2c/busses/i2c-tegra.c |   19 +++++++++++++------
>  1 files changed, 13 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
> index b402435..15ad866 100644
> --- a/drivers/i2c/busses/i2c-tegra.c
> +++ b/drivers/i2c/busses/i2c-tegra.c
> @@ -705,8 +705,9 @@ static int tegra_i2c_remove(struct platform_device *pdev)
>  }
>  
>  #ifdef CONFIG_PM
> -static int tegra_i2c_suspend(struct platform_device *pdev, pm_message_t state)
> +static int tegra_i2c_suspend_noirq(struct device *dev)
>  {
> +	struct platform_device *pdev = to_platform_device(dev);
>  	struct tegra_i2c_dev *i2c_dev = platform_get_drvdata(pdev);
>  
>  	i2c_lock_adapter(&i2c_dev->adapter);
> @@ -716,8 +717,9 @@ static int tegra_i2c_suspend(struct platform_device *pdev, pm_message_t state)
>  	return 0;
>  }
>  
> -static int tegra_i2c_resume(struct platform_device *pdev)
> +static int tegra_i2c_resume_noirq(struct device *dev)
>  {
> +	struct platform_device *pdev = to_platform_device(dev);
>  	struct tegra_i2c_dev *i2c_dev = platform_get_drvdata(pdev);
>  	int ret;
>  
> @@ -736,6 +738,14 @@ static int tegra_i2c_resume(struct platform_device *pdev)
>  
>  	return 0;
>  }
> +
> +static const struct dev_pm_ops tegra_i2c_dev_pm_ops = {
> +	.suspend_noirq = tegra_i2c_suspend_noirq,
> +	.resume_noirq = tegra_i2c_resume_noirq,
> +};
> +#define TEGRA_I2C_DEV_PM_OPS (&tegra_i2c_dev_pm_ops)
> +#else
> +#define TEGRA_I2C_DEV_PM_OPS NULL
>  #endif
>  
>  #if defined(CONFIG_OF)
> @@ -752,14 +762,11 @@ MODULE_DEVICE_TABLE(of, tegra_i2c_of_match);
>  static struct platform_driver tegra_i2c_driver = {
>  	.probe   = tegra_i2c_probe,
>  	.remove  = tegra_i2c_remove,
> -#ifdef CONFIG_PM
> -	.suspend = tegra_i2c_suspend,
> -	.resume  = tegra_i2c_resume,
> -#endif
>  	.driver  = {
>  		.name  = "tegra-i2c",
>  		.owner = THIS_MODULE,
>  		.of_match_table = tegra_i2c_of_match,
> +		.pm    = TEGRA_I2C_DEV_PM_OPS,
>  	},
>  };
>  
> -- 
> 1.7.0.4
> 
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