Re: [Patch V4] i2c: imx: add runtime pm support to improve the performance

[Heiner Kallweit <hkallweit1-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Am 25.08.2015 um 04:20 schrieb Gao Pan:
> In our former i2c driver, i2c clk is enabled and disabled in
> xfer function, which contributes to power saving. However,
> the clk enable process brings a busy wait delay until the core
> is stable. As a result, the performance is sacrificed.
> 
> To weigh the power consumption and i2c bus performance, runtime
> pm is the good solution for it. The clk is enabled when a i2c
> transfer starts, and disabled after a specifically defined delay.
> 
> Without the patch the test case (many eeprom reads) executes with approx:
> real 1m7.735s
> user 0m0.488s
> sys 0m20.040s
> 
> With the patch the same test case (many eeprom reads) executes with approx:
> real 0m54.241s
> user 0m0.440s
> sys 0m5.920s
> 
> Signed-off-by: Fugang Duan <B38611-KZfg59tc24xl57MIdRCFDg@public.gmane.org>
> Signed-off-by: Gao Pan <b54642-KZfg59tc24xl57MIdRCFDg@public.gmane.org>
> [wsa: fixed some indentation]
> Signed-off-by: Wolfram Sang <wsa-z923LK4zBo2bacvFa/9K2g@public.gmane.org>
> ---
> V2:
> As Uwe Kleine-König's suggestion, the version do below changes:
>  -call clk_prepare_enable in probe to avoid never enabling clock
>   if CONFIG_PM is disabled
>  -enable clock before request IRQ in probe
>  -remove the pm staff in i2c_imx_isr
> 
> V3:
>  -pm_runtime_get_sync returns < 0 as error
> 
> V4:
>  -add pm_runtime_set_active before pm_runtime_enable
>  -replace pm_runtime_put_autosuspend with pm_runtime_autosuspend
>   in probe
>  -add error disposal when i2c_add_numbered_adapter fails
> 
>  drivers/i2c/busses/i2c-imx.c | 79 ++++++++++++++++++++++++++++++++++++++------
>  1 file changed, 68 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
> index 785aa67..7c63047 100644
> --- a/drivers/i2c/busses/i2c-imx.c
> +++ b/drivers/i2c/busses/i2c-imx.c
> @@ -53,6 +53,7 @@
>  #include <linux/platform_device.h>
>  #include <linux/sched.h>
>  #include <linux/slab.h>
> +#include <linux/pm_runtime.h>
>  
>  /** Defines ********************************************************************
>  *******************************************************************************/
> @@ -118,6 +119,8 @@
>  #define I2CR_IEN_OPCODE_0	0x0
>  #define I2CR_IEN_OPCODE_1	I2CR_IEN
>  
> +#define I2C_PM_TIMEOUT		10 /* ms */
> +
>  /** Variables ******************************************************************
>  *******************************************************************************/
>  
> @@ -520,9 +523,6 @@ static int i2c_imx_start(struct imx_i2c_struct *i2c_imx)
>  
>  	i2c_imx_set_clk(i2c_imx);
>  
> -	result = clk_prepare_enable(i2c_imx->clk);
> -	if (result)
> -		return result;
>  	imx_i2c_write_reg(i2c_imx->ifdr, i2c_imx, IMX_I2C_IFDR);
>  	/* Enable I2C controller */
>  	imx_i2c_write_reg(i2c_imx->hwdata->i2sr_clr_opcode, i2c_imx, IMX_I2C_I2SR);
> @@ -575,7 +575,6 @@ static void i2c_imx_stop(struct imx_i2c_struct *i2c_imx)
>  	/* Disable I2C controller */
>  	temp = i2c_imx->hwdata->i2cr_ien_opcode ^ I2CR_IEN,
>  	imx_i2c_write_reg(temp, i2c_imx, IMX_I2C_I2CR);
> -	clk_disable_unprepare(i2c_imx->clk);
>  }
>  
>  static irqreturn_t i2c_imx_isr(int irq, void *dev_id)
> @@ -894,6 +893,10 @@ static int i2c_imx_xfer(struct i2c_adapter *adapter,
>  
>  	dev_dbg(&i2c_imx->adapter.dev, "<%s>\n", __func__);
>  
> +	result = pm_runtime_get_sync(i2c_imx->adapter.dev.parent);
> +	if (result < 0)
> +		goto out;
> +
>  	/* Start I2C transfer */
>  	result = i2c_imx_start(i2c_imx);
>  	if (result)
> @@ -950,6 +953,10 @@ fail0:
>  	/* Stop I2C transfer */
>  	i2c_imx_stop(i2c_imx);
>  
> +out:
> +	pm_runtime_mark_last_busy(i2c_imx->adapter.dev.parent);
> +	pm_runtime_put_autosuspend(i2c_imx->adapter.dev.parent);
> +
>  	dev_dbg(&i2c_imx->adapter.dev, "<%s> exit with: %s: %d\n", __func__,
>  		(result < 0) ? "error" : "success msg",
>  			(result < 0) ? result : num);
> @@ -1020,9 +1027,10 @@ static int i2c_imx_probe(struct platform_device *pdev)
>  
>  	ret = clk_prepare_enable(i2c_imx->clk);
>  	if (ret) {
> -		dev_err(&pdev->dev, "can't enable I2C clock\n");
> +		dev_err(&pdev->dev, "can't enable I2C clock, ret=%d\n", ret);
>  		return ret;
>  	}
> +
>  	/* Request IRQ */
>  	ret = devm_request_irq(&pdev->dev, irq, i2c_imx_isr, 0,
>  				pdev->name, i2c_imx);
> @@ -1037,6 +1045,14 @@ static int i2c_imx_probe(struct platform_device *pdev)
>  	/* Set up adapter data */
>  	i2c_set_adapdata(&i2c_imx->adapter, i2c_imx);
>  
> +	/* Set up platform driver data */
> +	platform_set_drvdata(pdev, i2c_imx);
> +
> +	pm_runtime_set_autosuspend_delay(&pdev->dev, I2C_PM_TIMEOUT);
> +	pm_runtime_use_autosuspend(&pdev->dev);
> +	pm_runtime_set_active(&pdev->dev);
> +	pm_runtime_enable(&pdev->dev);
> +
>  	/* Set up clock divider */
>  	i2c_imx->bitrate = IMX_I2C_BIT_RATE;
>  	ret = of_property_read_u32(pdev->dev.of_node,
> @@ -1053,12 +1069,13 @@ static int i2c_imx_probe(struct platform_device *pdev)
>  	ret = i2c_add_numbered_adapter(&i2c_imx->adapter);
>  	if (ret < 0) {
>  		dev_err(&pdev->dev, "registration failed\n");
> +		pm_runtime_mark_last_busy(&pdev->dev);
> +		pm_runtime_autosuspend(&pdev->dev);
It would be more consistent with the general practice not to clean up here
but to define a new error label, goto there and do the clean-up there.
And if adding the adapter fails most likely you don't want to autosuspend
but clean up and disable runtime PM.
>  		goto clk_disable;
>  	}
>  
> -	/* Set up platform driver data */
> -	platform_set_drvdata(pdev, i2c_imx);
> -	clk_disable_unprepare(i2c_imx->clk);
> +	pm_runtime_mark_last_busy(&pdev->dev);
> +	pm_runtime_autosuspend(&pdev->dev);
>From enabling runtime PM to here you don't hold a reference so theoretically
it might happen that the device gets suspended in-between.
I'm not able to say whether this is an actual potential issue here.
However to be on the safe side it wouldn't hurt to do a pm_runtime_get_xx
when enabling PM and use pm_runtime_put_autosuspend here.

Regards, Heiner
>  
>  	dev_dbg(&i2c_imx->adapter.dev, "claimed irq %d\n", irq);
>  	dev_dbg(&i2c_imx->adapter.dev, "device resources: %pR\n", res);
> @@ -1079,6 +1096,11 @@ clk_disable:
>  static int i2c_imx_remove(struct platform_device *pdev)
>  {
>  	struct imx_i2c_struct *i2c_imx = platform_get_drvdata(pdev);
> +	int ret;
> +
> +	ret = pm_runtime_get_sync(&pdev->dev);
> +	if (ret < 0)
> +		return ret;
>  
>  	/* remove adapter */
>  	dev_dbg(&i2c_imx->adapter.dev, "adapter removed\n");
> @@ -1093,17 +1115,52 @@ static int i2c_imx_remove(struct platform_device *pdev)
>  	imx_i2c_write_reg(0, i2c_imx, IMX_I2C_I2CR);
>  	imx_i2c_write_reg(0, i2c_imx, IMX_I2C_I2SR);
>  
> +	pm_runtime_put_sync(&pdev->dev);
> +	pm_runtime_disable(&pdev->dev);
> +
>  	return 0;
>  }
>  
> +#ifdef CONFIG_PM
> +static int i2c_imx_runtime_suspend(struct device *dev)
> +{
> +	struct imx_i2c_struct *i2c_imx  = dev_get_drvdata(dev);
> +
> +	clk_disable_unprepare(i2c_imx->clk);
> +
> +	return 0;
> +}
> +
> +static int i2c_imx_runtime_resume(struct device *dev)
> +{
> +	struct imx_i2c_struct *i2c_imx  = dev_get_drvdata(dev);
> +	int ret;
> +
> +	ret = clk_prepare_enable(i2c_imx->clk);
> +	if (ret)
> +		dev_err(dev, "can't enable I2C clock, ret=%d\n", ret);
> +
> +	return ret;
> +}
> +
> +static const struct dev_pm_ops i2c_imx_pm_ops = {
> +	SET_RUNTIME_PM_OPS(i2c_imx_runtime_suspend,
> +			   i2c_imx_runtime_resume, NULL)
> +};
> +#define I2C_IMX_PM_OPS (&i2c_imx_pm_ops)
> +#else
> +#define I2C_IMX_PM_OPS NULL
> +#endif /* CONFIG_PM */
> +
>  static struct platform_driver i2c_imx_driver = {
>  	.probe = i2c_imx_probe,
>  	.remove = i2c_imx_remove,
> -	.driver	= {
> -		.name	= DRIVER_NAME,
> +	.driver = {
> +		.name = DRIVER_NAME,
> +		.pm = I2C_IMX_PM_OPS,
>  		.of_match_table = i2c_imx_dt_ids,
>  	},
> -	.id_table	= imx_i2c_devtype,
> +	.id_table = imx_i2c_devtype,
>  };
>  
>  static int __init i2c_adap_imx_init(void)
>