linux-kernel - RE: [PATCH] clk: imx: gate off peripheral clock slice

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Date:   Fri, 22 Oct 2021 12:46:20 +0000
From:   Peng Fan <peng.fan@....com>
To:     Ahmad Fatoum <a.fatoum@...gutronix.de>,
        "Peng Fan (OSS)" <peng.fan@....nxp.com>,
        "sboyd@...nel.org" <sboyd@...nel.org>,
        "mturquette@...libre.com" <mturquette@...libre.com>,
        Abel Vesa <abel.vesa@....com>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH] clk: imx: gate off peripheral clock slice

Hi Ahmad,

> Subject: Re: [PATCH] clk: imx: gate off peripheral clock slice
> 
> Hello Peng,
> 
> On 22.10.21 15:09, Peng Fan (OSS) wrote:
> > From: Peng Fan <peng.fan@....com>
> >
> > The Peripheral clocks are default enabled when SoC power on, and
> > bootloader not gate off the clocks when booting Linux Kernel.
> >
> > So Linux Kernel is not aware the peripheral clocks are enabled and
> > still take them as disabled because of enable count is zero.
> >
> > Then Peripheral clock's source without clock gated off could be
> > changed when have assigned-parents in device tree
> >
> > However, per i.MX8M* reference mannual, "Peripheral clock slices must
> > be stopped to change the clock source", so need to gate off the the
> > peripheral clock when registering the clocks to avoid glitch.
> 
> This sounds like a fix that should be backported. If so, could you provide a
> Fixes: Tag?

We not see any critical issue without this patch, just to avoid
any potential risk here. So I not add fix tag here.

Abel, do you prefer a fixes tag or leave it as is?

Thanks,
Peng.

> 
> Thanks,
> Ahmad
> 
> >
> > Tested boot on i.MX8MM/P-EVK board
> >
> > Signed-off-by: Peng Fan <peng.fan@....com>
> > ---
> >  drivers/clk/imx/clk-composite-8m.c | 9 ++++++++-
> >  1 file changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/clk/imx/clk-composite-8m.c
> > b/drivers/clk/imx/clk-composite-8m.c
> > index 2dfd6149e528..ee41fbf90589 100644
> > --- a/drivers/clk/imx/clk-composite-8m.c
> > +++ b/drivers/clk/imx/clk-composite-8m.c
> > @@ -184,6 +184,7 @@ struct clk_hw *__imx8m_clk_hw_composite(const
> char *name,
> >  	struct clk_mux *mux = NULL;
> >  	const struct clk_ops *divider_ops;
> >  	const struct clk_ops *mux_ops;
> > +	u32 val;
> >
> >  	mux = kzalloc(sizeof(*mux), GFP_KERNEL);
> >  	if (!mux)
> > @@ -216,8 +217,14 @@ struct clk_hw *__imx8m_clk_hw_composite(const
> char *name,
> >  		div->width = PCG_PREDIV_WIDTH;
> >  		divider_ops = &imx8m_clk_composite_divider_ops;
> >  		mux_ops = &clk_mux_ops;
> > -		if (!(composite_flags & IMX_COMPOSITE_FW_MANAGED))
> > +		if (!(composite_flags & IMX_COMPOSITE_FW_MANAGED)) {
> >  			flags |= CLK_SET_PARENT_GATE;
> > +			if (!(flags & CLK_IS_CRITICAL)) {
> > +				val = readl(reg);
> > +				val &= ~BIT(PCG_CGC_SHIFT);
> > +				writel(val, reg);
> > +			}
> > +		}
> >  	}
> >
> >  	div->lock = &imx_ccm_lock;
> >
> 
> 
> --
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