Re: [PATCH] [RFC] qcom_scm: hide Kconfig symbol

[Will Deacon <will@xxxxxxxxxx>]

On Mon, Sep 27, 2021 at 05:22:13PM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
> 
> Now that SCM can be a loadable module, we have to add another
> dependency to avoid link failures when ipa or adreno-gpu are
> built-in:
> 
> aarch64-linux-ld: drivers/net/ipa/ipa_main.o: in function `ipa_probe':
> ipa_main.c:(.text+0xfc4): undefined reference to `qcom_scm_is_available'
> 
> ld.lld: error: undefined symbol: qcom_scm_is_available
> >>> referenced by adreno_gpu.c
> >>>               gpu/drm/msm/adreno/adreno_gpu.o:(adreno_zap_shader_load) in archive drivers/built-in.a
> 
> This can happen when CONFIG_ARCH_QCOM is disabled and we don't select
> QCOM_MDT_LOADER, but some other module selects QCOM_SCM. Ideally we'd
> use a similar dependency here to what we have for QCOM_RPROC_COMMON,
> but that causes dependency loops from other things selecting QCOM_SCM.
> 
> This appears to be an endless problem, so try something different this
> time:
> 
>  - CONFIG_QCOM_SCM becomes a hidden symbol that nothing 'depends on'
>    but that is simply selected by all of its users
> 
>  - All the stubs in include/linux/qcom_scm.h can go away
> 
>  - arm-smccc.h needs to provide a stub for __arm_smccc_smc() to
>    allow compile-testing QCOM_SCM on all architectures.
> 
>  - To avoid a circular dependency chain involving RESET_CONTROLLER
>    and PINCTRL_SUNXI, change the 'depends on RESET_CONTROLLER' in
>    the latter one to 'select'.
> 
> The last bit is rather annoying, as drivers should generally never
> 'select' another subsystem, and about half the users of the reset
> controller interface do this anyway.
> 
> Nevertheless, this version seems to pass all my randconfig tests
> and is more robust than any of the prior versions.
> 
> Comments?
> 
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
>  drivers/firmware/Kconfig                |  4 +-
>  drivers/gpu/drm/msm/Kconfig             |  4 +-
>  drivers/iommu/Kconfig                   |  2 +-
>  drivers/media/platform/Kconfig          |  2 +-
>  drivers/mmc/host/Kconfig                |  2 +-
>  drivers/net/ipa/Kconfig                 |  1 +
>  drivers/net/wireless/ath/ath10k/Kconfig |  2 +-
>  drivers/pinctrl/qcom/Kconfig            |  3 +-
>  drivers/pinctrl/sunxi/Kconfig           |  6 +--
>  include/linux/arm-smccc.h               | 10 ++++
>  include/linux/qcom_scm.h                | 71 -------------------------
>  11 files changed, 23 insertions(+), 84 deletions(-)
> 
> diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
> index 220a58cf0a44..f7dd82ef0b9c 100644
> --- a/drivers/firmware/Kconfig
> +++ b/drivers/firmware/Kconfig
> @@ -203,9 +203,7 @@ config INTEL_STRATIX10_RSU
>  	  Say Y here if you want Intel RSU support.
>  
>  config QCOM_SCM
> -	tristate "Qcom SCM driver"
> -	depends on ARM || ARM64
> -	depends on HAVE_ARM_SMCCC
> +	tristate
>  	select RESET_CONTROLLER
>  
>  config QCOM_SCM_DOWNLOAD_MODE_DEFAULT
> diff --git a/drivers/gpu/drm/msm/Kconfig b/drivers/gpu/drm/msm/Kconfig
> index e9c6af78b1d7..3ddf739a6f9b 100644
> --- a/drivers/gpu/drm/msm/Kconfig
> +++ b/drivers/gpu/drm/msm/Kconfig
> @@ -17,7 +17,7 @@ config DRM_MSM
>  	select DRM_SCHED
>  	select SHMEM
>  	select TMPFS
> -	select QCOM_SCM if ARCH_QCOM
> +	select QCOM_SCM
>  	select WANT_DEV_COREDUMP
>  	select SND_SOC_HDMI_CODEC if SND_SOC
>  	select SYNC_FILE
> @@ -55,7 +55,7 @@ config DRM_MSM_GPU_SUDO
>  
>  config DRM_MSM_HDMI_HDCP
>  	bool "Enable HDMI HDCP support in MSM DRM driver"
> -	depends on DRM_MSM && QCOM_SCM
> +	depends on DRM_MSM
>  	default y
>  	help
>  	  Choose this option to enable HDCP state machine
> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> index 124c41adeca1..989c83acbfee 100644
> --- a/drivers/iommu/Kconfig
> +++ b/drivers/iommu/Kconfig
> @@ -308,7 +308,7 @@ config APPLE_DART
>  config ARM_SMMU
>  	tristate "ARM Ltd. System MMU (SMMU) Support"
>  	depends on ARM64 || ARM || (COMPILE_TEST && !GENERIC_ATOMIC64)
> -	depends on QCOM_SCM || !QCOM_SCM #if QCOM_SCM=m this can't be =y
> +	select QCOM_SCM
>  	select IOMMU_API
>  	select IOMMU_IO_PGTABLE_LPAE
>  	select ARM_DMA_USE_IOMMU if ARM

I don't want to get in the way of this patch because I'm also tired of the
randconfig failures caused by QCOM_SCM. However, ARM_SMMU is applicable to
a wide variety of (non-qcom) SoCs and so it seems a shame to require the
QCOM_SCM code to be included for all of those when it's not strictly needed
at all.

Will