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Message-ID: <9f6b243b-0642-41db-85ed-d020bfa3e6e2@kernel.org> Date: Sat, 9 Nov 2024 11:20:09 +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 09/11/2024 11:05, Krzysztof Kozlowski wrote: > On 09/11/2024 01:37, Peng Fan wrote: >>> 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. >> >> >> CCM: Clock Control Module, it accepts PLL from anatop as inputs, >> and outputs clocks to various modules, I2C, CAN, NET, SAI and ... >> >>> >>> >>>> >>>> >>>>> 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? >> >> I hope we are on same page of what spread spectrum means. >> spread spectrum of a clock is the clock could produce freq in a range, >> saying [500MHz - 100KHz, 500MHz + 100KHz]. software only need >> to configure the middle frequency and choose the up/down border >> range(100KHz here) and enable spread spectrum. >> >> device: I suppose you mean the Clock Control Module(CCM) here. > > I mean the device we discuss here, in this binding. Whatever this device > is. CCM or CCX > >> CCM does not care, it just accepts the PLL as input, and output > > Takes PLL as input but you refuse to add it as clocks? Are you really > responding to my question? > > I asked how can you set spread spectrum on clock which you do not > receive. Why you do not receive? Because you refuse to add it to clocks > even though I speak about this since months. > >> divided clock to various IPs(Video here). The video IPs care about >> the spread spectrum of the clock. > > So which device do we talk about? I am not a NXP clock developer and I > care zero about NXP, so keep it simple. We discuss this one specific > binding for specific device which is called "imx8m-clock" - see subject > prefix. > >> >> The clock hardware path is as below: >> >> OSC(24M) --> Anatop(produce PLL with spread spectrum) -> >> Clock Control Module(output clock to modules) -> Video IP >> >> From hardware perspective, Clock Control Module does not >> care spread spectrum. Video IP cares spread spectrum. >> >> >>> >>> Why would you care about spread spectrum of some clock which is not >>> coming to this device? >> >> device, I suppose you mean clock control module(CCM). >> >> There is no 'clocks = <&ccm CLK_IMX8M_VIDEO_PLL>' under ccm node. >> Because in current design, ccm is taken as producer of >> CLK_IMX8M_VIDEO_PLL, not consumer. > > I don't understand now even more. Or I understand even less now. Why > binding references its own clocks via phandle? This makes no sense at > all, except of course assigned clocks, but that's because we have one > property for multiple cases. And BTW if that was the point then the example is confusing because the &clk phandle is not the device node in the example but it should. Neither description says which device's clocks are these. This is expressed very poorly in the binding, look: "Phandles of the PLL" - it clearly suggests some other clocks, not its own, that's so obvious I did not even think of asking. Patchset goes slow also because of poor explanation, lack of diagrams and expecting me to remember your clock hierarchy. Best regards, Krzysztof
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