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

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Message-ID: <CABGWkvpj2bYyqiOp4D9Ss2aWOnoR7BxqDOGpXdRusq=aWu9BEA@mail.gmail.com>
Date: Sat, 25 Jan 2025 13:58:30 +0100
From: Dario Binacchi <dario.binacchi@...rulasolutions.com>
To: "Peng Fan (OSS)" <peng.fan@....nxp.com>
Cc: 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>, 
	Krzysztof Kozlowski <krzk@...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 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
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.

Thanks and regards,
Dario

> [1] https://github.com/devicetree-org/dt-schema/pull/154
>
> Signed-off-by: Peng Fan <peng.fan@....com>
> ---
> Peng Fan (3):
>       clk: Introduce clk_set_spread_spectrum
>       clk: conf: Support assigned-clock-sscs
>       clk: scmi: Support spread spectrum
>
>  drivers/clk/clk-conf.c        | 68 +++++++++++++++++++++++++++++++++++++++++++
>  drivers/clk/clk-scmi.c        | 37 +++++++++++++++++++++++
>  drivers/clk/clk.c             | 39 +++++++++++++++++++++++++
>  include/linux/clk-provider.h  | 22 ++++++++++++++
>  include/linux/clk.h           | 22 ++++++++++++++
>  include/linux/scmi_protocol.h |  5 ++++
>  6 files changed, 193 insertions(+)
> ---
> base-commit: 5ffa57f6eecefababb8cbe327222ef171943b183
> change-id: 20250124-clk-ssc-fccd4f60d7e5
>
> Best regards,
> --
> Peng Fan <peng.fan@....com>
>


-- 

Dario Binacchi

Senior Embedded Linux Developer

dario.binacchi@...rulasolutions.com

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