[v2,1/2] i2c: imx: use clk notifier for rate changes

Instead of repeatedly calling clk_get_rate for each transfer, register
a clock notifier to update the cached divider value each time the clock
rate actually changes.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
---
v2: Don't use a static notifier block, as this is unsafe with multiple
    i2c-imx driver instances.
---
 drivers/i2c/busses/i2c-imx.c | 32 +++++++++++++++++++++++++-------
 1 file changed, 25 insertions(+), 7 deletions(-)

Hi Lucas, Wolfram,

On Thu, 2018-03-08 at 14:25 +0100, Lucas Stach wrote:
> Instead of repeatedly calling clk_get_rate for each transfer, register
> a clock notifier to update the cached divider value each time the clock
> rate actually changes.
> 
> Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
> ---
> v2: Don't use a static notifier block, as this is unsafe with multiple
>     i2c-imx driver instances.

This removes the need to lock the clk_prepare mutex with every i2c
transfer just to check the rate of a clock that never changes on many
systems.
With the embedded notifier block this now looks safe to handle unlikely
changes of the i2c module clock.

Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>

regards
Philipp

> ---
>  drivers/i2c/busses/i2c-imx.c | 32 +++++++++++++++++++++++++-------
>  1 file changed, 25 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
> index 999557729ad2..c9632b2f0eaa 100644
> --- a/drivers/i2c/busses/i2c-imx.c
> +++ b/drivers/i2c/busses/i2c-imx.c
> @@ -194,6 +194,7 @@ struct imx_i2c_dma {
>  struct imx_i2c_struct {
>  	struct i2c_adapter	adapter;
>  	struct clk		*clk;
> +	struct notifier_block	clk_change_nb;
>  	void __iomem		*base;
>  	wait_queue_head_t	queue;
>  	unsigned long		i2csr;
> @@ -467,15 +468,14 @@ static int i2c_imx_acked(struct imx_i2c_struct *i2c_imx)
>  	return 0;
>  }
>  
> -static void i2c_imx_set_clk(struct imx_i2c_struct *i2c_imx)
> +static void i2c_imx_set_clk(struct imx_i2c_struct *i2c_imx,
> +			    unsigned int i2c_clk_rate)
>  {
>  	struct imx_i2c_clk_pair *i2c_clk_div = i2c_imx->hwdata->clk_div;
> -	unsigned int i2c_clk_rate;
>  	unsigned int div;
>  	int i;
>  
>  	/* Divider value calculation */
> -	i2c_clk_rate = clk_get_rate(i2c_imx->clk);
>  	if (i2c_imx->cur_clk == i2c_clk_rate)
>  		return;
>  
> @@ -510,6 +510,20 @@ static void i2c_imx_set_clk(struct imx_i2c_struct *i2c_imx)
>  #endif
>  }
>  
> +static int i2c_imx_clk_notifier_call(struct notifier_block *nb,
> +				     unsigned long action, void *data)
> +{
> +	struct clk_notifier_data *ndata = data;
> +	struct imx_i2c_struct *i2c_imx = container_of(&ndata->clk,
> +						      struct imx_i2c_struct,
> +						      clk);
> +
> +	if (action & POST_RATE_CHANGE)
> +		i2c_imx_set_clk(i2c_imx, ndata->new_rate);
> +
> +	return NOTIFY_OK;
> +}
> +
>  static int i2c_imx_start(struct imx_i2c_struct *i2c_imx)
>  {
>  	unsigned int temp = 0;
> @@ -517,8 +531,6 @@ static int i2c_imx_start(struct imx_i2c_struct *i2c_imx)
>  
>  	dev_dbg(&i2c_imx->adapter.dev, "<%s>\n", __func__);
>  
> -	i2c_imx_set_clk(i2c_imx);
> -
>  	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);
> @@ -1131,6 +1143,9 @@ static int i2c_imx_probe(struct platform_device *pdev)
>  				   "clock-frequency", &i2c_imx->bitrate);
>  	if (ret < 0 && pdata && pdata->bitrate)
>  		i2c_imx->bitrate = pdata->bitrate;
> +	i2c_imx->clk_change_nb.notifier_call = i2c_imx_clk_notifier_call;
> +	clk_notifier_register(i2c_imx->clk, &i2c_imx->clk_change_nb);
> +	i2c_imx_set_clk(i2c_imx, clk_get_rate(i2c_imx->clk));
>  
>  	/* Set up chip registers to defaults */
>  	imx_i2c_write_reg(i2c_imx->hwdata->i2cr_ien_opcode ^ I2CR_IEN,
> @@ -1141,12 +1156,12 @@ static int i2c_imx_probe(struct platform_device *pdev)
>  	ret = i2c_imx_init_recovery_info(i2c_imx, pdev);
>  	/* Give it another chance if pinctrl used is not ready yet */
>  	if (ret == -EPROBE_DEFER)
> -		goto rpm_disable;
> +		goto clk_notifier_unregister;
>  
>  	/* Add I2C adapter */
>  	ret = i2c_add_numbered_adapter(&i2c_imx->adapter);
>  	if (ret < 0)
> -		goto rpm_disable;
> +		goto clk_notifier_unregister;
>  
>  	pm_runtime_mark_last_busy(&pdev->dev);
>  	pm_runtime_put_autosuspend(&pdev->dev);
> @@ -1162,6 +1177,8 @@ static int i2c_imx_probe(struct platform_device *pdev)
>  
>  	return 0;   /* Return OK */
>  
> +clk_notifier_unregister:
> +	clk_notifier_unregister(i2c_imx->clk, &i2c_imx->clk_change_nb);
>  rpm_disable:
>  	pm_runtime_put_noidle(&pdev->dev);
>  	pm_runtime_disable(&pdev->dev);
> @@ -1195,6 +1212,7 @@ 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);
>  
> +	clk_notifier_unregister(i2c_imx->clk, &i2c_imx->clk_change_nb);
>  	clk_disable_unprepare(i2c_imx->clk);
>  
>  	pm_runtime_put_noidle(&pdev->dev);

On Thu, Mar 08, 2018 at 02:25:17PM +0100, Lucas Stach wrote:
> Instead of repeatedly calling clk_get_rate for each transfer, register
> a clock notifier to update the cached divider value each time the clock
> rate actually changes.
> 
> Signed-off-by: Lucas Stach <l.stach@pengutronix.de>

Applied to for-next, thanks!