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

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Message-ID:
 <PAXPR04MB8459FAD02E2530FAA21A568A883DA@PAXPR04MB8459.eurprd04.prod.outlook.com>
Date: Fri, 22 Aug 2025 02:35:26 +0000
From: Peng Fan <peng.fan@....com>
To: Arnd Bergmann <arnd@...db.de>, "Peng Fan (OSS)" <peng.fan@....nxp.com>
CC: 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>, "imx@...ts.linux.dev" <imx@...ts.linux.dev>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/3] firmware: imx: Add stub functions for SCMI MISC API

Hi Arnd,

> Subject: Re: [PATCH 1/3] firmware: imx: Add stub functions for SCMI
> MISC API
> 
> On Thu, Aug 21, 2025, at 11:56, Peng Fan wrote:
> > On Wed, Aug 20, 2025 at 03:55:20PM +0200, Arnd Bergmann wrote:
> >>On Thu, Aug 7, 2025, at 03:47, Peng Fan wrote:
> >>
> >>
> >>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.
> >
> > The consumer driver still needs Kconfig dependcies, such as
> >   depends on IMX_SCMI_MISC_DRV || !IMX_SCMI_MISC_DRV
> >
> > So when IMX_SCMI_MISC_DRV is module built, the consumer driver
> will
> > also be module built.
> >
> > But if IMX_SCMI_MISC_DRV is n, the consumer driver is y, there will
> be
> > link error.
> >
> > The consumer driver is to support platform A and platform B.
> >
> > Platform A does not require the real API in IMX_SCMI_MISC_DRV.
> > Platform B requires the real API in IMX_SCMI_MISC_DRV.
> >
> > So when producing an image for platform A, IMX_SCMI_MISC_DRV
> could set
> > to n to make Image smaller. Introducing the stub API is mainly for
> > this case.
> >
> > Hope this is clear
> 
> I see. In this case the stub helpers are not wrong, but I still find them
> more error-prone than not having them and using IS_ENABLED() checks
> as in commit 101c9023594a
> ("ASoC: fsl_mqs: Support accessing registers by scmi interface"):
> 
> +static int fsl_mqs_sm_read(void *context, unsigned int reg, unsigned
> +int *val) {
> +       struct fsl_mqs *mqs_priv = context;
> +       int num = 1;
> +
> +       if (IS_ENABLED(CONFIG_IMX_SCMI_MISC_DRV) &&
> +           mqs_priv->soc->ctrl_off == reg)
> +               return
> + scmi_imx_misc_ctrl_get(SCMI_IMX_CTRL_MQS1_SETTINGS, &num,
> val);
> +
> +       return -EINVAL;
> +};
> 
> The logic is the same here in the end, but the link failure is easier to
> trigger and repair if someone gets it wrong.
> 
> Also, for drivers that actually need the exported interface, the
> dependency becomes the simpler 'depends on IMX_SCMI_MISC_DRV'.

Yeah, but since consumer drivers supports multiple platforms,
if platform A not requires the real API in IMX_SCMI_MISC_DRV,
no need to link the real API.

> 
> Which driver using this symbol are you actually looking at? I see you
> have three similar patches for a couple of interfaces, and want to make
> sure the added complexity is really needed here. I do a lot of
> randconfig build tests, so quite often I end up being the one that runs
> into the subtle link failures from these.

The patch is here
https://lore.kernel.org/linux-remoteproc/20250821-imx95-rproc-1-v5-0-e93191dfac51@nxp.com/T/#macc660f61873742de447ac8c20d34f2d494ff712

Please help give a look.

Thanks,
Peng.

> 
>       Arnd