linux-kernel - Re: [PATCH 0/3] clk: Support spread spectrum and use it in clk-scmi

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Message-ID: <CABGWkvrUjQPOc+PnpNSp7Ag2HC6DLLAH-fqGdSwUSfo6Z=M+AQ@mail.gmail.com>
Date: Mon, 27 Jan 2025 09:35:44 +0100
From: Dario Binacchi <dario.binacchi@...rulasolutions.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: "Peng Fan (OSS)" <peng.fan@....nxp.com>, Michael Turquette <mturquette@...libre.com>, 
	Stephen Boyd <sboyd@...nel.org>, Russell King <linux@...linux.org.uk>, 
	Sudeep Holla <sudeep.holla@....com>, Cristian Marussi <cristian.marussi@....com>, 
	linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org, 
	arm-scmi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	Rob Herring <robh@...nel.org>, Shawn Guo <shawnguo@...nel.org>, 
	Sascha Hauer <s.hauer@...gutronix.de>, Pengutronix Kernel Team <kernel@...gutronix.de>, 
	Fabio Estevam <festevam@...il.com>, imx@...ts.linux.dev, Peng Fan <peng.fan@....com>
Subject: Re: [PATCH 0/3] clk: Support spread spectrum and use it in clk-scmi

On Mon, Jan 27, 2025 at 9:31 AM Krzysztof Kozlowski <krzk@...nel.org> wrote:
>
> On 27/01/2025 08:59, Dario Binacchi wrote:
> > On Mon, Jan 27, 2025 at 8:42 AM Krzysztof Kozlowski <krzk@...nel.org> wrote:
> >>
> >> On 25/01/2025 13:58, Dario Binacchi wrote:
> >>> On Fri, Jan 24, 2025 at 2:19 PM Peng Fan (OSS) <peng.fan@....nxp.com> wrote:
> >>>>
> >>>> - Introduce clk_set_spread_spectrum to set the parameters for enabling
> >>>>   spread spectrum of a clock.
> >>>> - Parse 'assigned-clock-sscs' and configure it by default before using the
> >>>>   clock. The pull request for this property is at [1]
> >>>>   This property is parsed before parsing clock rate.
> >>>>
> >>>> - Enable this feature for clk-scmi on i.MX95.
> >>>>   This may not the best, since checking machine compatibles.
> >>>>   I am thinking to provide an API scmi_get_vendor_info, then driver
> >>>>   could use it for OEM stuff, such as
> >>>>   if (scmi_get_vendor_info returns NXP_IMX)
> >>>>       ops->set_spread_spectrum = scmi_clk_set_spread_spectrum_imx;
> >>>>
> >>>
> >>> I wonder if your solution is truly generic or merely a generalization
> >>> of your use case, which seems significantly simpler compared to what
> >>
> >> Please come with specific arguments why this is not generic enough, not
> >> just FUD. Does it fit your case? If not, what would had to be changed?
> >> These are the comments needed to actually work on generic solution.
> >>
> >>> happens on the i.MX8M platform, as discussed in thread
> >>> https://lore.kernel.org/lkml/PAXPR04MB8459537D7D2A49221D0E890D88E32@PAXPR04MB8459.eurprd04.prod.outlook.com/,
> >>> or on the STM32F platform, where parameters are not written directly
> >>> to registers but are instead used in calculations involving the
> >>> parent_rate and the PLL divider, for example.
> >>>
> >>> I am the author of the patches that introduced spread spectrum
> >>> management for the AM33x and STM32Fx platforms, as well as the
> >>> series, still pending acceptance, for the i.MX8M.
> >>> From my perspective, this functionality varies significantly
> >>> from platform to platform, with key differences that must be
> >>> considered.
> >>
> >> So what exactly varies? Come with specifics.
> >
> > In all the cases I implemented, I enabled spread spectrum within
> > the set_rate of the clock/PLL in question, as information such as
> > the parent rate or the divisor used was necessary to perform the
> > calculations needed to extract the data for setting the SSCG
> > register bitfields.
> >
> > If I'm not mistaken, I think this is not the case implemented by this
> > series.
>
> It feels like you speak about driver, so I misunderstood the concerns. I
> did not check the drivers at all, so here I do not claim patchsets are
> compatible.

Yes, I commented on the driver.
For the dt-bindings I added a comment in the github PR
https://github.com/devicetree-org/dt-schema/pull/154

Thanks and regards,
Dario

>
> But the binding takes the same values - the main PLL/clock rate.
>
> Best regards,
> Krzysztof



-- 

Dario Binacchi

Senior Embedded Linux Developer

dario.binacchi@...rulasolutions.com

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