Re: [RFC 07/19] devfreq: imx8m-ddrc: Add late system sleep PM ops

[Chanwoo Choi <cwchoi00@gmail.com>]

On 21. 2. 20. 오전 1:00, Abel Vesa wrote:
> Seems that, in order to be able to resume from suspend, the dram rate
> needs to be the highest one available. Therefore, add the late system
> suspend/resume PM ops which set the highest rate on suspend and the
> latest one used before suspending on resume.
> 
> Signed-off-by: Abel Vesa <abel.vesa@nxp.com>
> ---
>   drivers/devfreq/imx8m-ddrc.c | 26 ++++++++++++++++++++++++++
>   1 file changed, 26 insertions(+)
> 
> diff --git a/drivers/devfreq/imx8m-ddrc.c b/drivers/devfreq/imx8m-ddrc.c
> index 33de83acfd8b..04347dee781b 100644
> --- a/drivers/devfreq/imx8m-ddrc.c
> +++ b/drivers/devfreq/imx8m-ddrc.c
> @@ -72,6 +72,8 @@ struct imx8m_ddrc {
>   	struct clk *dram_alt;
>   	struct clk *dram_apb;
>   
> +	unsigned long suspend_rate;
> +	unsigned long resume_rate;
>   	int freq_count;
>   	struct imx8m_ddrc_freq freq_table[IMX8M_DDRC_MAX_FREQ_COUNT];
>   };
> @@ -271,6 +273,22 @@ static int imx8m_ddrc_target(struct device *dev, unsigned long *freq, u32 flags)
>   	return ret;
>   }
>   
> +static int imx8m_ddrc_suspend(struct device *dev)
> +{
> +	struct imx8m_ddrc *priv = dev_get_drvdata(dev);
> +
> +	priv->resume_rate = clk_get_rate(priv->dram_core);
> +
> +	return imx8m_ddrc_target(dev, &priv->suspend_rate, 0);
> +}
> +
> +static int imx8m_ddrc_resume(struct device *dev)
> +{
> +	struct imx8m_ddrc *priv = dev_get_drvdata(dev);
> +
> +	return imx8m_ddrc_target(dev, &priv->resume_rate, 0);
> +}
> +
>   static int imx8m_ddrc_get_cur_freq(struct device *dev, unsigned long *freq)
>   {
>   	struct imx8m_ddrc *priv = dev_get_drvdata(dev);
> @@ -336,6 +354,9 @@ static int imx8m_ddrc_init_freq_info(struct device *dev)
>   
>   		if (dev_pm_opp_add(dev, freq->rate * 250000, 0))
>   			return -ENODEV;
> +
> +		if (index ==  0)
> +			priv->suspend_rate = freq->rate * 250000;
>   	}
>   
>   	return 0;
> @@ -412,10 +433,15 @@ static const struct of_device_id imx8m_ddrc_of_match[] = {
>   };
>   MODULE_DEVICE_TABLE(of, imx8m_ddrc_of_match);
>   
> +static const struct dev_pm_ops imx8m_ddrc_pm_ops = {
> +	SET_LATE_SYSTEM_SLEEP_PM_OPS(imx8m_ddrc_suspend, imx8m_ddrc_resume)
> +};

Are there any reason to use suspend_late instead of suspend?
Usually, it is enough to change the frequency on normal suspend() step.
The devfreq supports the 'opp-suspend' property[1]. If you keep the OPP 
entries on DT, you simply support your goal with 'opp-suspend'.

[1] 
https://elixir.bootlin.com/linux/latest/source/Documentation/devicetree/bindings/opp/opp.txt#L156

> +
>   static struct platform_driver imx8m_ddrc_platdrv = {
>   	.probe		= imx8m_ddrc_probe,
>   	.driver = {
>   		.name	= "imx8m-ddrc-devfreq",
> +		.pm = &imx8m_ddrc_pm_ops,
>   		.of_match_table = of_match_ptr(imx8m_ddrc_of_match),
>   	},
>   };
>