[PATCH] clk: imx: gate off peripheral clock slice

[PATCH] clk: imx: gate off peripheral clock slice

[Peng Fan (OSS)]

From: Peng Fan <peng.fan@nxp.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.

Tested boot on i.MX8MM/P-EVK board

Signed-off-by: Peng Fan <peng.fan@nxp.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;
-- 
2.30.0

Re: [PATCH] clk: imx: gate off peripheral clock slice

[Ahmad Fatoum]

Hello Peng,

On 22.10.21 15:09, Peng Fan (OSS) wrote:
> From: Peng Fan <peng.fan@nxp.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?

Thanks,
Ahmad

> 
> Tested boot on i.MX8MM/P-EVK board
> 
> Signed-off-by: Peng Fan <peng.fan@nxp.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;
> 


-- 
Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

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

[Peng Fan]

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@nxp.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@nxp.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;
> >
> 
> 
> --
> Pengutronix e.K.                           |
> |
> Steuerwalder Str. 21                       |
> https://eur01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.p
> engutronix.de%2F&amp;data=04%7C01%7Cpeng.fan%40nxp.com%7Cb5b827
> 20263e43680e9208d995597f48%7C686ea1d3bc2b4c6fa92cd99c5c301635%
> 7C0%7C0%7C637705033902868076%7CUnknown%7CTWFpbGZsb3d8eyJWIj
> oiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1
> 000&amp;sdata=PolK7YYK66Bbyd6KJgINnvma8JZ6OdDZ8e1cp6rvIww%3D&a
> mp;reserved=0  |
> 31137 Hildesheim, Germany                  | Phone:
> +49-5121-206917-0    |
> Amtsgericht Hildesheim, HRA 2686           | Fax:
> +49-5121-206917-5555 |

Re: [PATCH] clk: imx: gate off peripheral clock slice

[Abel Vesa]

On 21-10-22 15:46:20, Peng Fan wrote:
> 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@nxp.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?
> 

Lets put a fixes tag still. That way, it will be backported and
it will probably save someone (who's maybe using an older kernel) a headache.
Plus, it will get in sooner.

> Thanks,
> Peng.
> 
> > 
> > Thanks,
> > Ahmad
> > 
> > >
> > > Tested boot on i.MX8MM/P-EVK board
> > >
> > > Signed-off-by: Peng Fan <peng.fan@nxp.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;
> > >
> > 
> > 
> > --
> > Pengutronix e.K.                           |
> > |
> > Steuerwalder Str. 21                       |
> > https://eur01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.p
> > engutronix.de%2F&amp;data=04%7C01%7Cpeng.fan%40nxp.com%7Cb5b827
> > 20263e43680e9208d995597f48%7C686ea1d3bc2b4c6fa92cd99c5c301635%
> > 7C0%7C0%7C637705033902868076%7CUnknown%7CTWFpbGZsb3d8eyJWIj
> > oiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1
> > 000&amp;sdata=PolK7YYK66Bbyd6KJgINnvma8JZ6OdDZ8e1cp6rvIww%3D&a
> > mp;reserved=0  |
> > 31137 Hildesheim, Germany                  | Phone:
> > +49-5121-206917-0    |
> > Amtsgericht Hildesheim, HRA 2686           | Fax:
> > +49-5121-206917-5555 |