Re: [PATCH v2 3/2] docs: changes: better document Python needs

[Mauro Carvalho Chehab <mchehab+huawei@kernel.org>]

Em Mon, 28 Jul 2025 12:28:45 +0300
Jani Nikula <jani.nikula@intel.com> escreveu:

> On Thu, 24 Jul 2025, Mauro Carvalho Chehab <mchehab+huawei@kernel.org> wrote:
> > Em Thu, 24 Jul 2025 08:42:59 -0600
> > Jonathan Corbet <corbet@lwn.net> escreveu:
> >
> >> Mauro Carvalho Chehab <mchehab+huawei@kernel.org> writes:
> >> 
> >> > Maybe I can place instead CONFIG_DRM_I915_WERROR.
> >> 
> >> I've held off on this series on the expectation that a new version would
> >> come.  I guess, at this point, it will be a post-merge-window thing?
> >
> > Feel free to postpone. I have already a new version of it here somewhere on
> > my branches, but I had to take some days off. So, I ended not sending you
> > the (probably) final version.
> >
> > I intend to send what I have here during the merge window for you to
> > review and apply post-merge-window.
> 
> I think the main questions here are 1) how to handle optional build tool
> dependencies, and 2) whether Python is an optional or required
> dependency.

with regards to (2), besides doc build and kernel-doc --none, there is
at least another place at the building system requiring Python: 
scripts/Makefile.vmlinux_o: There, it has:

	quiet_cmd_gen_initcalls_lds = GEN     $@
	      cmd_gen_initcalls_lds = \
	        $(PYTHON3) $(srctree)/scripts/jobserver-exec \
	        $(PERL) $(real-prereqs) > $@

	.tmp_initcalls.lds: $(srctree)/scripts/generate_initcall_order.pl \
	                vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE
	        $(call if_changed,gen_initcalls_lds)

	targets := .tmp_initcalls.lds

	ifdef CONFIG_LTO_CLANG
	initcalls-lds := .tmp_initcalls.lds
	endif

Now, I didn't check exactly what conditions trigger
.tmp_initcalls.lds, but there are some places that use
select:

	arch/Kconfig:   select LTO_CLANG

On a quick look, it sounds that some archs will select this
automatically when built with clang.

I didn't check if other parts of the building system requires it.

In any case, on its current state, I'd say that currently this
is not optional.

> It might be nice to be able to have an actual Kconfig and dependency for
> optional tools. "depends on TOOL_PYTHON" or something. Enable the
> option, and you should have Python.

That would be an option. The question is: is it worth spending
time on it?

> This in turn raises the question for allyesconfig. It's cumbersome
> (though not impossible) to add config options that you actually have to
> enable manually.

IMO it doesn't make sense to manually enable something with *config.
If they depend on Python, be it: for such targets, Python is
mandatory.

> 
> The header test stuff really isn't required to actually build the kernel
> or drm, however DRM_MSM does depend on Python for building the driver.

Good to know. It means that, for those *config targets:

	arch/arm/configs/imx_v6_v7_defconfig:CONFIG_DRM_MSM=y
	arch/arm/configs/multi_v7_defconfig:CONFIG_DRM_MSM=m
	arch/arm/configs/qcom_defconfig:CONFIG_DRM_MSM=m

(plus all{mod|yes}config)

Python is mandatory. As multi_v7_defconfig is one of them, we
may assume, that, o practical cases, Python 2.7 or 3.2+ is 
mandatory for arm support. The current requirement is:

	$ vermin -v --no-tips ./drivers/gpu/drm/msm/registers/gen_header.py
	Detecting python files..
	Analyzing using 8 processes..
	2.7, 3.2     /new_devel/v4l/docs/drivers/gpu/drm/msm/registers/gen_header.py
	Minimum required versions: 2.7, 3.2

Heh, looking for files that end with .py at Makefile (not all
Python scripts at the Kernel end with such extension), it seems
that there are more:

	grep \\\.py $(git ls-files|grep Makefile|grep -v tools)


	Makefile:KERNELDOC       = $(srctree)/scripts/kernel-doc.py
	Makefile:		  vmlinux-gdb.py \
	Makefile:	$(Q)ln -fsn $(abspath $(srctree)/scripts/gdb/vmlinux-gdb.py)
	Makefile:compile_commands.json: $(srctree)/scripts/clang-tools/gen_compile_commands.py \
	Makefile:      cmd_clang_tools = $(PYTHON3) $(srctree)/scripts/clang-tools/run-clang-tools.py $@ $<
	drivers/gpu/drm/msm/Makefile:      cmd_headergen = mkdir -p $(obj)/generated && $(PYTHON3) $(src)/registers/gen_header.py \
	drivers/gpu/drm/msm/Makefile:		$(src)/registers/gen_header.py \
	drivers/gpu/drm/msm/Makefile:		$(src)/registers/gen_header.py \
	drivers/tty/vt/Makefile:#GENERATE_UCS_TABLES := 2  # invokes gen_ucs_recompose_table.py with --full
	drivers/tty/vt/Makefile:$(obj)/ucs_width_table.h: $(src)/gen_ucs_width_table.py
	drivers/tty/vt/Makefile:$(obj)/ucs_recompose_table.h: $(src)/gen_ucs_recompose_table.py
	drivers/tty/vt/Makefile:$(obj)/ucs_fallback_table.h: $(src)/gen_ucs_fallback_table.py
	rust/Makefile:	$(Q)MAKEFLAGS= $(srctree)/scripts/generate_rust_analyzer.py \
	scripts/Makefile.lib:MAKE_FIT := $(srctree)/scripts/make_fit.py
	scripts/gdb/linux/Makefile:symlinks := $(patsubst $(src)/%,%,$(wildcard $(src)/*.py))
	scripts/gdb/linux/Makefile:always-y += constants.py
	scripts/gdb/linux/Makefile:$(obj)/constants.py: $(src)/constants.py.in FORCE
	scripts/gdb/linux/Makefile:clean-files := *.pyc *.pyo

(that not including tools/*)

Some seem false positives, but on the other hand, looking for tools,
several scripts seem to be executed by non-tools Makefiles. I didn't
check if any of them are written in python, though.

Considering the above, for me it seems that the bus already 
departed: there are several cases where Python is required during
build time. So, adding a "depends on TOOL_PYTHON" doesn't seem
to be trivial.

From my side, I don't mind much about that, as this is something
that affects only the Kernel build. I would very much prefer to
have things like config BPF optional.

Regards,
Mauro