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

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Message-ID: <5165cc5e-4ba3-45a8-8bc0-6ff6f379c4af@kernel.org>
Date: Mon, 27 Jan 2025 09:31:25 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Dario Binacchi <dario.binacchi@...rulasolutions.com>
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 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.

But the binding takes the same values - the main PLL/clock rate.

Best regards,
Krzysztof