linux-kernel - Re: [PATCH V2] firmware: arm_scmi: bus: bypass set fwnode for scmi cpufreq

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Message-ID: <20240813085703.zz6ltcxmrrbdgt77@lcpd911>
Date: Tue, 13 Aug 2024 14:27:03 +0530
From: Dhruva Gole <d-gole@...com>
To: "Peng Fan (OSS)" <peng.fan@....nxp.com>
CC: <sudeep.holla@....com>, <cristian.marussi@....com>, <saravanak@...gle.com>,
        <linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <arm-scmi@...r.kernel.org>, Peng Fan
	<peng.fan@....com>
Subject: Re: [PATCH V2] firmware: arm_scmi: bus: bypass set fwnode for scmi
 cpufreq

On Jul 29, 2024 at 15:03:25 +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

The commit message itself seems very specific to some platform to me.
What about platforms that don't atall have a GPU? Why would they care
about this?

> device not ready.
> 
> Because for cpufreq, no need use fw_devlink. So bypass setting fwnode
> for scmi cpufreq device.
> 
> Fixes: 96da4a99ce50 ("firmware: arm_scmi: Set fwnode for the scmi_device")
> Signed-off-by: Peng Fan <peng.fan@....com>
> ---
> 
> V2:
>  Use A!=B to replace !(A == B)
>  Add fixes tag
>  This might be a workaround, but since this is a fix, it is simple for
>  backporting.

More than a workaround, it feels like a HACK to me.

> 
> V1:
>  https://lore.kernel.org/all/20240717093515.327647-1-peng.fan@oss.nxp.com/
> 
>  drivers/firmware/arm_scmi/bus.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/firmware/arm_scmi/bus.c b/drivers/firmware/arm_scmi/bus.c
> index 96b2e5f9a8ef..be91a82e0cda 100644
> --- a/drivers/firmware/arm_scmi/bus.c
> +++ b/drivers/firmware/arm_scmi/bus.c
> @@ -395,7 +395,8 @@ __scmi_device_create(struct device_node *np, struct device *parent,
>  	scmi_dev->id = id;
>  	scmi_dev->protocol_id = protocol;
>  	scmi_dev->dev.parent = parent;
> -	device_set_node(&scmi_dev->dev, of_fwnode_handle(np));
> +	if ((protocol != SCMI_PROTOCOL_PERF) || strcmp(name, "cpufreq"))
> +		device_set_node(&scmi_dev->dev, of_fwnode_handle(np));

I kind of disagree with the idea here to be specific about the
PROTOCOL_PERF or cpufreq. This is a generic arm scmi bus driver right?
Why bring in specific code into a bus driver? We will never fix the
actual root cause of the issue this way.

-- 
Best regards,
Dhruva Gole <d-gole@...com>