linux-kernel - Re: [PATCH 1/3] firmware: imx: Add stub functions for SCMI MISC API

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Message-Id: <2ff85fec-b571-4423-9161-674f88a32e18@app.fastmail.com>
Date: Wed, 20 Aug 2025 15:55:20 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: "Peng Fan" <peng.fan@....com>, "Shawn Guo" <shawnguo@...nel.org>,
 "Sascha Hauer" <s.hauer@...gutronix.de>,
 "Pengutronix Kernel Team" <kernel@...gutronix.de>,
 "Fabio Estevam" <festevam@...il.com>, "Sudeep Holla" <sudeep.holla@....com>,
 "Cristian Marussi" <cristian.marussi@....com>
Cc: imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] firmware: imx: Add stub functions for SCMI MISC API

On Thu, Aug 7, 2025, at 03:47, Peng Fan wrote:
> To ensure successful builds when CONFIG_IMX_SCMI_MISC_DRV is not enabled,
> this patch adds static inline stub implementations for the following
> functions:
>
>   - scmi_imx_misc_ctrl_get()
>   - scmi_imx_misc_ctrl_set()
>
> These stubs return -EOPNOTSUPP to indicate that the functionality is not
> supported in the current configuration. This avoids potential build or
> link errors in code that conditionally calls these functions based on
> feature availability.
>
> Fixes: 540c830212ed ("firmware: imx: remove duplicate scmi_imx_misc_ctrl_get()")
> Fixes: 0b4f8a68b292 ("firmware: imx: Add i.MX95 MISC driver")
> Signed-off-by: Peng Fan <peng.fan@....com>
> ---

I don't think this does what you describe, at least not reliably:
 
> +#if IS_ENABLED(CONFIG_IMX_SCMI_MISC_DRV)
>  int scmi_imx_misc_ctrl_get(u32 id, u32 *num, u32 *val);
>  int scmi_imx_misc_ctrl_set(u32 id, u32 val);
> +#else
> +static inline int scmi_imx_misc_ctrl_get(u32 id, u32 *num, u32 *val)
> +{
> +	return -EOPNOTSUPP;
> +}

When a caller of this function is in a built-in driver but the
IMX_SCMI_MISC_DRV code is in a loadable module, you still
get a link failure, see 514b2262ade4 ("firmware: arm_scmi:
Fix i.MX build dependency") for an example.

As you still need the correct Kconfig dependencies, I
think your patch here is not helpful.

     Arnd