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Date:	Mon, 20 Oct 2014 14:39:14 +0200
From:	Ludovic Desroches <ludovic.desroches@...el.com>
To:	Wenyou Yang <wenyou.yang@...el.com>
CC:	<wsa@...-dreams.de>, <ludovic.desroches@...el.com>,
	<linux-i2c@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<nicolas.ferre@...el.com>, <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/3] i2c/at91: add support for runtime PM

Hi Wenyou,

On Mon, Oct 20, 2014 at 11:42:12AM +0800, Wenyou Yang wrote:
> Drivers should put the device into low power states proactively whenever the
> device is not in use. Thus implement support for runtime PM and use the
> autosuspend feature to make sure that we can still perform well in case we see
> lots of i2c traffic within short period of time.
> 
> Signed-off-by: Wenyou Yang <wenyou.yang@...el.com>
> ---
>  drivers/i2c/busses/i2c-at91.c |   48 ++++++++++++++++++++++++++++++++---------
>  1 file changed, 38 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-at91.c b/drivers/i2c/busses/i2c-at91.c
> index 917d545..03b9f48 100644
> --- a/drivers/i2c/busses/i2c-at91.c
> +++ b/drivers/i2c/busses/i2c-at91.c
> @@ -31,10 +31,12 @@
>  #include <linux/platform_device.h>
>  #include <linux/slab.h>
>  #include <linux/platform_data/dma-atmel.h>
> +#include <linux/pm_runtime.h>
>  
>  #define DEFAULT_TWI_CLK_HZ		100000		/* max 400 Kbits/s */
>  #define AT91_I2C_TIMEOUT	msecs_to_jiffies(100)	/* transfer timeout */
>  #define AT91_I2C_DMA_THRESHOLD	8			/* enable DMA if transfer size is bigger than this threshold */
> +#define AUTOSUSPEND_TIMEOUT		2000
>  
>  /* AT91 TWI register definitions */
>  #define	AT91_TWI_CR		0x0000	/* Control Register */
> @@ -475,12 +477,16 @@ error:
>  static int at91_twi_xfer(struct i2c_adapter *adap, struct i2c_msg *msg, int num)
>  {
>  	struct at91_twi_dev *dev = i2c_get_adapdata(adap);
> -	int ret;
> +	int ret = 0;

Not necessary.

>  	unsigned int_addr_flag = 0;
>  	struct i2c_msg *m_start = msg;
>  
>  	dev_dbg(&adap->dev, "at91_xfer: processing %d messages:\n", num);
>  
> +	ret = pm_runtime_get_sync(dev->dev);
> +	if (ret < 0)
> +		goto out;
> +
>  	/*
>  	 * The hardware can handle at most two messages concatenated by a
>  	 * repeated start via it's internal address feature.
> @@ -488,18 +494,21 @@ static int at91_twi_xfer(struct i2c_adapter *adap, struct i2c_msg *msg, int num)
>  	if (num > 2) {
>  		dev_err(dev->dev,
>  			"cannot handle more than two concatenated messages.\n");
> -		return 0;
> +		ret = 0;
> +		goto out;
>  	} else if (num == 2) {
>  		int internal_address = 0;
>  		int i;
>  
>  		if (msg->flags & I2C_M_RD) {
>  			dev_err(dev->dev, "first transfer must be write.\n");
> -			return -EINVAL;
> +			ret = -EINVAL;
> +			goto out;
>  		}
>  		if (msg->len > 3) {
>  			dev_err(dev->dev, "first message size must be <= 3.\n");
> -			return -EINVAL;
> +			ret = -EINVAL;
> +			goto out;
>  		}
>  
>  		/* 1st msg is put into the internal address, start with 2nd */
> @@ -523,7 +532,13 @@ static int at91_twi_xfer(struct i2c_adapter *adap, struct i2c_msg *msg, int num)
>  
>  	ret = at91_do_twi_transfer(dev);
>  
> -	return (ret < 0) ? ret : num;
> +	if (ret == 0)

I don't figure out why you've changed this condition.

> +		ret = num;
> +out:
> +	pm_runtime_mark_last_busy(dev->dev);
> +	pm_runtime_put_autosuspend(dev->dev);
> +
> +	return ret;
>  }
>  
>  static u32 at91_twi_func(struct i2c_adapter *adapter)
> @@ -795,11 +810,20 @@ static int at91_twi_probe(struct platform_device *pdev)
>  	dev->adapter.timeout = AT91_I2C_TIMEOUT;
>  	dev->adapter.dev.of_node = pdev->dev.of_node;
>  
> +	pm_runtime_set_autosuspend_delay(dev->dev, AUTOSUSPEND_TIMEOUT);
> +	pm_runtime_use_autosuspend(dev->dev);
> +	pm_runtime_set_active(dev->dev);
> +	pm_runtime_enable(dev->dev);
> +
>  	rc = i2c_add_numbered_adapter(&dev->adapter);
>  	if (rc) {
>  		dev_err(dev->dev, "Adapter %s registration failed\n",
>  			dev->adapter.name);
>  		clk_disable_unprepare(dev->clk);
> +
> +		pm_runtime_disable(dev->dev);
> +		pm_runtime_set_suspended(dev->dev);
> +
>  		return rc;
>  	}
>  
> @@ -814,16 +838,19 @@ static int at91_twi_remove(struct platform_device *pdev)
>  	i2c_del_adapter(&dev->adapter);
>  	clk_disable_unprepare(dev->clk);
>  
> +	pm_runtime_disable(dev->dev);
> +	pm_runtime_set_suspended(dev->dev);
> +
>  	return 0;
>  }
>  
>  #ifdef CONFIG_PM
> -
> +#ifdef CONFIG_PM_RUNTIME
>  static int at91_twi_runtime_suspend(struct device *dev)
>  {
>  	struct at91_twi_dev *twi_dev = dev_get_drvdata(dev);
>  
> -	clk_disable(twi_dev->clk);
> +	clk_disable_unprepare(twi_dev->clk);
>  
>  	return 0;
>  }
> @@ -832,12 +859,13 @@ static int at91_twi_runtime_resume(struct device *dev)
>  {
>  	struct at91_twi_dev *twi_dev = dev_get_drvdata(dev);
>  
> -	return clk_enable(twi_dev->clk);
> +	return clk_prepare_enable(twi_dev->clk);
>  }
> +#endif
>  
>  static const struct dev_pm_ops at91_twi_pm = {
> -	.runtime_suspend	= at91_twi_runtime_suspend,
> -	.runtime_resume		= at91_twi_runtime_resume,
> +	SET_RUNTIME_PM_OPS(at91_twi_runtime_suspend,
> +				at91_twi_runtime_resume, NULL)
>  };
>  
>  #define at91_twi_pm_ops (&at91_twi_pm)
> -- 
> 1.7.9.5
> 


Regards

Ludovic
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