linux-kernel - Re: [PATCH v3 1/8] dt-bindings: clock: imx8m-clock: support spread spectrum clocking

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Message-ID: <8c310eca-d695-418c-82cb-a89351d83887@kernel.org>
Date: Fri, 8 Nov 2024 15:10:58 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Peng Fan <peng.fan@....com>,
 Dario Binacchi <dario.binacchi@...rulasolutions.com>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "linux-amarula@...rulasolutions.com" <linux-amarula@...rulasolutions.com>,
 Abel Vesa <abelvesa@...nel.org>, Conor Dooley <conor+dt@...nel.org>,
 Fabio Estevam <festevam@...il.com>, Krzysztof Kozlowski
 <krzk+dt@...nel.org>, Michael Turquette <mturquette@...libre.com>,
 Pengutronix Kernel Team <kernel@...gutronix.de>,
 Rob Herring <robh@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>,
 Shawn Guo <shawnguo@...nel.org>, Stephen Boyd <sboyd@...nel.org>,
 "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
 "imx@...ts.linux.dev" <imx@...ts.linux.dev>,
 "linux-arm-kernel@...ts.infradead.org"
 <linux-arm-kernel@...ts.infradead.org>,
 "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>
Subject: Re: [PATCH v3 1/8] dt-bindings: clock: imx8m-clock: support spread
 spectrum clocking

On 08/11/2024 13:50, Peng Fan wrote:
>> Subject: Re: [PATCH v3 1/8] dt-bindings: clock: imx8m-clock: support
>> spread spectrum clocking
>>
>> On 07/11/2024 15:57, Dario Binacchi wrote:
>>>     clocks = <&osc_32k>, <&osc_24m>, <&clk_ext1>, <&clk_ext2>,
>>>                   <&clk_ext3>, <&clk_ext4>;
>>>     clock-names = "osc_32k", "osc_24m", "clk_ext1", "clk_ext2",
>>>                              "clk_ext3", "clk_ext4";
>>>     assigned-clocks = <&clk IMX8MN_CLK_A53_SRC>,
>>>                                   <&clk IMX8MN_CLK_A53_CORE>,
>>>                                   <&clk IMX8MN_CLK_NOC>,
>>>                                   <&clk IMX8MN_CLK_AUDIO_AHB>,
>>>                                   <&clk IMX8MN_CLK_IPG_AUDIO_ROOT>,
>>>                                   <&clk IMX8MN_SYS_PLL3>,
>>>                                   <&clk IMX8MN_AUDIO_PLL1>,
>>>                                   <&clk IMX8MN_AUDIO_PLL2>;
>>>     assigned-clock-parents = <&clk IMX8MN_SYS_PLL1_800M>,
>>>                                              <&clk IMX8MN_ARM_PLL_OUT>,
>>>                                              <&clk IMX8MN_SYS_PLL3_OUT>,
>>>                                              <&clk IMX8MN_SYS_PLL1_800M>;
>>>     assigned-clock-rates = <0>, <0>, <0>,
>>>                                          <400000000>,
>>>                                          <400000000>,
>>>                                          <600000000>,
>>>                                          <393216000>,
>>>                                          <361267200>; };
>>>
>>> The spread spectrum is not configurable on these clocks or, more
>>> generally, may not be configurable (only 4 PLLs have this capability).
>>> Therefore, I need the "fsl,ssc-clocks"
>>
>> No. That's not true. You do not need it.
>>
> 
> i.MX8M clock hardware is similar as:
> 
> OSC->ANATOP->CCM
> 
> ANATOP will produce PLLs.
> CCM use PLLs as input source.
> 
> Currently there is no dedicated ANATOP driver in linux.
> The CCM linux driver will parse the ANATOP node and
> register clk_hw for the PLLs.

I do not know what is CCM and how does it fit here. What's more, I don't
get driver context here. We talk about bindings.


> 
> 
>> First, the clock inputs for this device are listed in clocks *only*.
>> What is no there, is not an input to the device. Including also Linux
>> aspect (missing devlinks etc). Therefore how can you configure spread
>> spectrum on clocks which are not connected to this device?
> 
> I not understand this well, you mean
> add clocks = <xx CLK_IMX8MM_VIDEO_PLL> in the ccm dtb node?

Yes. Let me re-iterate and please respond to this exactly comment
instead of ignoring it.

How a device can care about spread spectrum of a clock which is not
supplied to this device?

Why would you care about spread spectrum of some clock which is not
coming to this device?

Please address these precisely because we talk about this for weeks in
multiple places. I finish with this patchset if you do not provide such
context.

Best regards,
Krzysztof