linux-kernel - Re: [PATCH 1/4] firmware: arm_scmi: bus: Bypass setting fwnode for scmi cpufreq

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Message-ID: <20250212070120.GD15796@localhost.localdomain>
Date: Wed, 12 Feb 2025 15:01:20 +0800
From: Peng Fan <peng.fan@....nxp.com>
To: Sudeep Holla <sudeep.holla@....com>
Cc: Cristian Marussi <cristian.marussi@....com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Saravana Kannan <saravanak@...gle.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Dong Aisheng <aisheng.dong@....com>,
	Fabio Estevam <festevam@...il.com>, Shawn Guo <shawnguo@...nel.org>,
	Jacky Bai <ping.bai@....com>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Sascha Hauer <s.hauer@...gutronix.de>, arm-scmi@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-gpio@...r.kernel.org, imx@...ts.linux.dev,
	Peng Fan <peng.fan@....com>
Subject: Re: [PATCH 1/4] firmware: arm_scmi: bus: Bypass setting fwnode for
 scmi cpufreq

On Tue, Feb 11, 2025 at 05:13:21PM +0000, Sudeep Holla wrote:
>On Wed, Dec 25, 2024 at 04:20:44PM +0800, Peng Fan (OSS) wrote:
>> From: Peng Fan <peng.fan@....com>
>> 
>> Two drivers scmi_cpufreq.c and scmi_perf_domain.c both use
>> SCMI_PROTCOL_PERF protocol, but with different name, so two scmi devices
>> will be created. But the fwnode->dev could only point to one device.
>> 
>> If scmi cpufreq device created earlier, the fwnode->dev will point to
>> the scmi cpufreq device. Then the fw_devlink will link performance
>> domain user device(consumer) to the scmi cpufreq device(supplier).
>> But actually the performance domain user device, such as GPU, should use
>> the scmi perf device as supplier. Also if 'cpufreq.off=1' in bootargs,
>> the GPU driver will defer probe always, because of the scmi cpufreq
>> device not ready.
>> 
>> Because for cpufreq, no need use fw_devlink. So bypass setting fwnode
>> for scmi cpufreq device.
>>
>
>Not 100% sure if above is correct. See:
>
>Commit 8410e7f3b31e ("cpufreq: scmi: Fix OPP addition failure with a dummy clock provider")
>
>Am I missing something ?

Could we update juno-scmi.dtsi to use ?

 &A53_0 {
-       clocks = <&scmi_dvfs 1>;
+       power-domains = <&scmi_perf x>;
+       power-domain-names = "perf";
 };

Even for scmi-cpufreq.c that needs fw_devlink because of the clocks entry in
juno-scmi.dtsi, there is no issue here.
Because the dummy clock provider will always be ready before opp with
your upper fix. So we could safetly ignore fw_devlink per my understanding.

Regards,
Peng

>
>-- 
>Regards,
>Sudeep