Re: [PATCH V3 2/2] thermal: imx: add necessary clk operation

[Eduardo Valentin <eduardo.valentin@ti.com>]

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On 19-12-2013 17:16, Anson Huang wrote:
> Thermal sensor needs pll3_usb_otg when measuring temperature,
> otherwise the temperature read will be incorrect, so need to
> enable this clk before sensor working, for alarm function,
> as hardware will take measurement periodically, so we should
> keep this clk always on once alarm function is enabled.
> 
> Signed-off-by: Anson Huang <b20788@freescale.com>
> ---
>  .../devicetree/bindings/thermal/imx-thermal.txt    |    4 ++++
>  drivers/thermal/imx_thermal.c                      |   18 ++++++++++++++++++
>  2 files changed, 22 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/thermal/imx-thermal.txt b/Documentation/devicetree/bindings/thermal/imx-thermal.txt
> index 541c25e..1f0f672 100644
> --- a/Documentation/devicetree/bindings/thermal/imx-thermal.txt
> +++ b/Documentation/devicetree/bindings/thermal/imx-thermal.txt
> @@ -8,10 +8,14 @@ Required properties:
>    calibration data, e.g. OCOTP on imx6q.  The details about calibration data
>    can be found in SoC Reference Manual.
>  
> +Optional properties:
> +- clocks : thermal sensor's clock source.
> +
>  Example:
>  
>  tempmon {
>  	compatible = "fsl,imx6q-tempmon";
>  	fsl,tempmon = <&anatop>;
>  	fsl,tempmon-data = <&ocotp>;
> +	clocks = <&clks 172>;
>  };
> diff --git a/drivers/thermal/imx_thermal.c b/drivers/thermal/imx_thermal.c
> index 1d6c801..c2b8173 100644
> --- a/drivers/thermal/imx_thermal.c
> +++ b/drivers/thermal/imx_thermal.c
> @@ -7,6 +7,7 @@
>   *
>   */
>  
> +#include <linux/clk.h>
>  #include <linux/cpu_cooling.h>
>  #include <linux/cpufreq.h>
>  #include <linux/delay.h>
> @@ -73,6 +74,7 @@ struct imx_thermal_data {
>  	unsigned long last_temp;
>  	bool irq_enabled;
>  	int irq;
> +	struct clk *thermal_clk;
>  };
>  
>  static void imx_set_alarm_temp(struct imx_thermal_data *data,
> @@ -457,6 +459,22 @@ static int imx_thermal_probe(struct platform_device *pdev)
>  		return ret;
>  	}
>  

There are several reg writes before this point. Are you sure you won't
need this clock for performing those operations?

> +	data->thermal_clk = devm_clk_get(&pdev->dev, NULL);
> +	if (IS_ERR(data->thermal_clk)) {
> +		dev_warn(&pdev->dev, "failed to get thermal clk!\n");
> +	} else {
> +		/*
> +		 * Thermal sensor needs clk on to get correct value, normally
> +		 * we should enable its clk before taking measurement and disable
> +		 * clk after measurement is done, but if alarm function is enabled,
> +		 * hardware will auto measure the temperature periodically, so we
> +		 * need to keep the clk always on for alarm function.
> +		 */
> +		ret = clk_prepare_enable(data->thermal_clk);
> +		if (ret)
> +			dev_warn(&pdev->dev, "failed to enable thermal clk: %d\n", ret);
> +	}
> +
>  	/* Enable measurements at ~ 10 Hz */
>  	regmap_write(map, TEMPSENSE1 + REG_CLR, TEMPSENSE1_MEASURE_FREQ);
>  	measure_freq = DIV_ROUND_UP(32768, 10); /* 10 Hz */
> 

Don't you need to release the clock when .remove is called either on
driver or device removal?

What about suspend / resume path? Do you want to keep this clock on when
suspending? Is it gonna work or prevent your system to enter low power
states?



-- 
You have got to be excited about what you are doing. (L. Lamport)

Eduardo Valentin


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