linux-kernel - Re: [RFC 06/19] devfreq: imx8m-ddrc: Add late system sleep PM ops

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Date:   Mon, 25 Oct 2021 23:59:19 +0300
From:   Abel Vesa <abel.vesa@....com>
To:     Chanwoo Choi <cwchoi00@...il.com>
Cc:     Rob Herring <robh@...nel.org>, Dong Aisheng <aisheng.dong@....com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Georgi Djakov <djakov@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Ahmad Fatoum <a.fatoum@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        linux-serial@...r.kernel.org, NXP Linux Team <linux-imx@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        devicetree@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC 06/19] devfreq: imx8m-ddrc: Add late system sleep PM ops

On 21-09-15 12:37:45, Chanwoo Choi wrote:
> Hi,
> 
> As I commented on patch5, you keep the OPP list on devicetree file
> and then you better to use the 'suspend_opp' property
> for setting the highest frequency during suspend/resume.
> 

Hi,

I think there is no mechanism in place to ensure that the suspend opp
will be set only after all the icc users have suspended. I only tested
briefly, but I can tell you that there are cases where some icc user
asks for a different opp right after the suspend opp was set. This leads
to suspending with a different rate than the one from suspend opp.
So I guess I still need the late system sleep pm opps to circumvent such
situations.

> On 21. 9. 14. 오전 2:38, 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@....com>
> > ---
> >   drivers/devfreq/imx8m-ddrc.c | 28 +++++++++++++++++++++++++++-
> >   1 file changed, 27 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/devfreq/imx8m-ddrc.c b/drivers/devfreq/imx8m-ddrc.c
> > index f18a5c3c1c03..f39741b4a0b0 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);
> > @@ -324,6 +342,9 @@ 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;
> > @@ -399,11 +420,16 @@ 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)
> > +};
> > +
> >   static struct platform_driver imx8m_ddrc_platdrv = {
> >   	.probe		= imx8m_ddrc_probe,
> >   	.driver = {
> >   		.name	= "imx8m-ddrc-devfreq",
> > -		.of_match_table = imx8m_ddrc_of_match,
> > +		.pm = &imx8m_ddrc_pm_ops,
> > +		.of_match_table = of_match_ptr(imx8m_ddrc_of_match),
> >   	},
> >   };
> >   module_platform_driver(imx8m_ddrc_platdrv);
> > 
> 
> 
> -- 
> Best Regards,
> Samsung Electronics
> Chanwoo Choi