On Mon, Oct 11, 2021 at 11:10 AM Dmitry Baryshkov
[off-list ref] wrote:

On Mon, 11 Oct 2021 at 09:09, Arnd Bergmann [off-list ref] wrote:

quoted

On Mon, Oct 11, 2021 at 6:11 AM Dmitry Baryshkov
[off-list ref] wrote:

quoted

On Sun, 10 Oct 2021 at 20:42, Arnd Bergmann [off-list ref] wrote:

The patch seems correct, but it becomes overcomplicated. What about:
- restoring QCOM_SCM stubs

The stubs are what has led to the previous bugs in this area to often
go unnoticed for too long, as illustrated by your suggestion

quoted

- making ARM_SMMU select QCOM_SCM if ARM_SMMU_QCOM

I assume you meant "select QCOM_SCM if ARCH_QCOM",
after we stop using ARM_SMMU_QCOM?

quoted

This would have almost the same result as with your patch, but without
extra ARM_SMMU_QCOM Kconfig symbol.

The "almost" is the problem: consider the case of

CONFIG_ARM=y
CONFIG_COMPILE_TEST=y
CONFIG_ARCH_QCOM=n
CONFIG_ARM_SMMU=y
CONFIG_DRM_MSM=m
CONFIG_QCOM_SCM=m (selected by DRM_MSM)

The stubs here lead to ARM_SMMU linking against the QCOM_SCM
driver from built-in code, which fails because QCOM_SCM itself
is a loadable module.

I see. The idealist in me wishes to change my suggestion to
'select QCOM_SCM if ARCH_QCOM || COMPILE_TEST'
but I have the subtle feeling that this also might fail somehow.

I think that would actually work, but it has the nasty side-effect
that simply flipping 'CONFIG_COMPILE_TEST' changes what
the kernel does, rather than just hiding or unhiding additional
options.

quoted

We can move the "select QCOM_SCM" in the ARM_SMMU_QCOM
symbol if we make that a tristate though, if you want to separate it
a little more.

This would complicate things a bit, as we would no longer be able to
use 'arm-smmu-$(CONFIG_ARM_SMMU_QCOM) +=' construct.

I'm fairly sure we could still use that, Kbuild is smart enough
to include both 'file-m +=' and 'file-y += ' in 'file.ko', see
scripts/Makefile.lib:

# If $(foo-objs), $(foo-y), $(foo-m), or $(foo-) exists, foo.o is a
composite object
multi-obj-y := $(call multi-search, $(obj-y), .o, -objs -y)
multi-obj-m := $(call multi-search, $(obj-m), .o, -objs -y -m)
multi-obj-ym := $(multi-obj-y) $(multi-obj-m)

# Replace multi-part objects by their individual parts,
# including built-in.a from subdirectories
real-obj-y := $(call real-search, $(obj-y), .o, -objs -y)
real-obj-m := $(call real-search, $(obj-m), .o, -objs -y -m)

What doesn't work is having a built-in driver in a directory that is
guarded with a =m symbol, or including a =m object into a =y
module.

        Arnd

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