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

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Message-ID:
 <PAXPR04MB8459BE3474EFD4FCC28E0E82885D2@PAXPR04MB8459.eurprd04.prod.outlook.com>
Date: Fri, 8 Nov 2024 12:50:34 +0000
From: Peng Fan <peng.fan@....com>
To: Krzysztof Kozlowski <krzk@...nel.org>, 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

> 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.


> 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?

Currently the CLK_IMX8MM_VIDEO_PLL is registers by CCM driver,
so impossible the add the upper clocks, unless a dedicated
anatop driver is developed.

Thanks
Peng.

> 
> Second, I do no ask you to configure spread spectrum on other clocks,
> only on the ones you intent to. List is fixed and ordered, so no problem
> with that.
> 
> > property to list the PLLs on which I want to enable and configure
> > spread spectrum.
> >
> > Furthermore, spread spectrum cannot be considered a new device
> but
> > rather a property available only for some of the clocks managed by
> the
> > clock controller manager (CCM).




> >
> 
> My comment stands and that's a disagreement from me. Feel free to
> get second DT maintainer opinion, though.
> 
> Best regards,
> Krzysztof
>