Re: [PATCH V2] clk: imx: gate off peripheral clock slice

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

Hello Peng, Abel,

On 25.10.21 14:08, Abel Vesa wrote:
> On 21-10-25 20:29:02, 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

I just noticed this breaks earlycon on an i.MX8MN, I assume because
the earlycon driver will access unclocked registers.

On the i.MX8MN, I also noticed that disabling usb_phy_ref hangs the
system, whether via sysfs or via this patch. Still trying to figure
that one out.

Cheers,
Ahmad

>> Fixes: d3ff9728134e ("clk: imx: Add imx composite clock")
>> Signed-off-by: Peng Fan <peng.fan@nxp.com>
>> ---
>>
>> 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);
>> +			}
>> +		}
> 
> Though I'm usually against special cases like this one. I think the clock
> core needs some generic flag that would read the state from HW on probe
> and/or another generic flag for disabling on probe.
> 
> But for now, I'm OK with this:
> 
> Reviewed-by: Abel Vesa <abel.vesa@nxp.com>
> 
>>  	}
>>  
>>  	div->lock = &imx_ccm_lock;
>> -- 
>> 2.30.0
>>
> 
> 


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