linux-kernel - Re: [PATCH v4 05/14] soc: mediatek: mtk-svs: use svs clk control APIs

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Date:   Wed, 1 Feb 2023 12:28:56 +0000
From:   Roger Lu (陸瑞傑) <Roger.Lu@...iatek.com>
To:     "eballetbo@...il.com" <eballetbo@...il.com>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "khilman@...nel.org" <khilman@...nel.org>,
        "sboyd@...nel.org" <sboyd@...nel.org>,
        "drinkcat@...gle.com" <drinkcat@...gle.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        Project_Global_Chrome_Upstream_Group 
        <Project_Global_Chrome_Upstream_Group@...iatek.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Jia-wei Chang (張佳偉) 
        <Jia-wei.Chang@...iatek.com>,
        Fan Chen (陳凡) <fan.chen@...iatek.com>
Subject: Re: [PATCH v4 05/14] soc: mediatek: mtk-svs: use svs clk control APIs

Hi Matthias Sir,

On Tue, 2023-01-31 at 14:19 +0100, Matthias Brugger wrote:
> 
> On 11/01/2023 08:45, Roger Lu wrote:
> > In MediaTek HW design, svs and thermal both use the same clk source.
> > It means that svs clk reference count from CCF includes thermal control
> > counts. That makes svs driver confuse whether it disabled svs's main clk
> > or not from CCF's perspective and lead to turn off their shared clk
> > unexpectedly. Therefore, we add svs clk control APIs to make sure svs's
> > main clk is controlled well by svs driver itself.
> > 
> > Here is a NG example. Rely on CCF's reference count and cause problem.
> > 
> > thermal probe (clk ref = 1)
> > -> svs probe (clk ref = 2)
> >     -> svs suspend (clk ref = 1)
> >        -> thermal suspend (clk ref = 0)
> >        -> thermal resume (clk ref = 1)
> >     -> svs resume (encounter error, clk ref = 1)
> >     -> svs suspend (clk ref = 0)
> >        -> thermal suspend (Fail here, thermal HW control w/o clk)
> > 
> > Fixes: a825d72f74a3 ("soc: mediatek: fix missing clk_disable_unprepare() on
> > err in svs_resume()")
> > Signed-off-by: Roger Lu <roger.lu@...iatek.com>
> 
> That looks wrong. Although I don't out of my mind, there should be a way to
> tell 
> the clock framework that this clock is shared between several devices.
> 
> I wonder if using clk_enable and clk_disable in svs_resume/suspend wouldn't
> be 
> enough.

Oh yes, Common Clock Framework (CCF) knows the clock shared between several
devices and maintains clock "on/off" by reference count.

We concern how to stop running svs_suspend() when svs clk is already disabled by
svs_resume(). Take an example as below, if we refers to __clk_is_enabled()
result for knowing svs clk status, it will return "true" all the time because
thermal clk is still on. This causes the problem mentioned in commit message.

static int svs_suspend(struct device *dev)
{
...
	if (!__clk_is_enabled(svsp->main_clk)) //always get `true`
		return 0;
...
}

> 
> Regards,
> Matthias

... [snip] ...