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Subject: Re: [PATCH V2] clk: imx: gate off peripheral clock slice
From:   Ahmad Fatoum <a.fatoum@pengutronix.de>
To:     "Peng Fan (OSS)" <peng.fan@oss.nxp.com>, sboyd@kernel.org,
        mturquette@baylibre.com, abel.vesa@nxp.com, s.hauer@pengutronix.de
Cc:     Peng Fan <peng.fan@nxp.com>, linux-kernel@vger.kernel.org,
        linux-imx@nxp.com, kernel@pengutronix.de, festevam@gmail.com,
        linux-clk@vger.kernel.org, linux-arm-kernel@lists.infradead.org
References: <20211025122902.1151-1-peng.fan@oss.nxp.com>
 <fc1ac63d-30c3-f309-7631-212ffa3f9de0@pengutronix.de>
Message-ID: <3eda3c8b-636b-9b83-a2f5-434fd2bdc832@pengutronix.de>
Date:   Mon, 25 Oct 2021 13:59:13 +0200
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On 25.10.21 13:54, Ahmad Fatoum wrote:
> On 25.10.21 14:29, 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.
>>
>> Tested boot on i.MX8MM/P-EVK board
>>
>> Fixes: d3ff9728134e ("clk: imx: Add imx composite clock")
>> Signed-off-by: Peng Fan <peng.fan@nxp.com>
> 
> I've been running an i.MX8MM-based system with this patch for a few days
> so far and no apparent issues:
> 
> Tested-by: Ahmad Fatoum <a.fatoum@pengutronix.de>

I see now that the duration of test isn't as important as the number
of boots (as this is a probe-time change). Still, I booted it a dozen
or so times and didn't notice anything different.

> 
>> ---
>>
>> V2:
>>  Add Fixes tag
>>
>>  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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