RE: [PATCH] firmware: arm_scmi: fix i.MX build dependency

[Peng Fan <peng.fan@xxxxxxx>]

> Subject: Re: [PATCH] firmware: arm_scmi: fix i.MX build dependency
> 
> On Sat, Nov 16, 2024 at 12:05:18AM +0100, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd@xxxxxxxx>
> >
> 
> Hi Arnd,
> 
> > The newly added SCMI vendor driver references functions in the
> > protocol driver but needs a Kconfig dependency to ensure it can link,
> > essentially the Kconfig dependency needs to be reversed to match
> the
> > link time dependency:
> >
> > arm-linux-gnueabi-ld: sound/soc/fsl/fsl_mqs.o: in function
> `fsl_mqs_sm_write':
> > fsl_mqs.c:(.text+0x1aa): undefined reference to
> `scmi_imx_misc_ctrl_set'
> > arm-linux-gnueabi-ld: sound/soc/fsl/fsl_mqs.o: in function
> `fsl_mqs_sm_read':
> > fsl_mqs.c:(.text+0x1ee): undefined reference to
> `scmi_imx_misc_ctrl_get'
> >
> 
> The SCMI drivers, like the newly added IMX_SCMI_MISC_DRV,
> generally make ue of the related vendor protocol like
> IMX_SCMI_MISC_EXT, BUT the SCMI stack is designed in a way that NO
> symbols are needed to be exported by the protocol layer (to avoid a
> huge and growing number of symbols exports)...so usually the current
> DRV-->PROTO dependency is fine.
> 
> In this case, AFAIU, it is the SCMI driver that in turn exports a few
> helpers that are used by another driver fsl_mqs, which in turn could be
> compiled and work with or without the SCMI stack, so with this patch
> we are artificially reversing the DRV<--PROTO dependency to solve this
> scenario in all the compillation scenarios...
> 
> ....BUT given that the IMX_SCMI_MISC_DRV is the one that should
> export the missing symbols could NOT this solved in a cleaner way,
> without adding the fake reverse dependency, by instead modifying the
> header of the driver with something like the classic:
> 
> --->8-----
> diff --git a/include/linux/firmware/imx/sm.h
> b/include/linux/firmware/imx/sm.h index
> 9b85a3f028d1..3a7a3ec367c5 100644
> --- a/include/linux/firmware/imx/sm.h
> +++ b/include/linux/firmware/imx/sm.h
> @@ -17,7 +17,19 @@
>  #define SCMI_IMX_CTRL_SAI4_MCLK                4       /* WAKE SAI4
> MCLK */
>  #define SCMI_IMX_CTRL_SAI5_MCLK                5       /* WAKE SAI5
> MCLK */
> 
> +#ifdef 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 0;
> +}
> +
> +static inline int scmi_imx_misc_ctrl_set(u32 id, u32 val) {
> +       return 0;
> +}
> +#endif
> 

This change is good to me. With just a difference that in downstream
we use -EOPNOTSUPP

https://github.com/nxp-imx/linux-imx/blob/lf-6.6.y/include/linux/firmware/imx/sm.h#L19

Thanks,
Peng.

>  #endif
> ----->8-----------
> 
> ....to just support compilation in all the scenarios.
> 
> > This however only works after changing the dependency in the
> > SND_SOC_FSL_MQS driver as well, which uses 'select
> IMX_SCMI_MISC_DRV'
> > to turn on a driver it depends on. This is generally a bad idea, so
> > the best solution is to change that into a dependency.
> >
> > To allow the ASoC driver to keep building with the SCMI support, this
> > needs to be an optional dependency that enforces the link-time
> > dependency if IMX_SCMI_MISC_DRV is a loadable module but not
> depend on
> > it if that is disabled.
> >
> 
> ...and maybe with the above additions you could avoid also these other
> dep changes...
> 
> ...not sure if I am missing something and I have definitely not tested
> any of my babbling above...
> 
> Thanks,
> Cristian