[PATCH v3 13/15] docs: sphinx: add a file with the requirements for lowest version

[Mauro Carvalho Chehab]

Those days, it is hard to install a virtual env that would
build docs with Sphinx 3.4.3, as even python 3.13 is not
compatible anymore with it.

	/usr/bin/python3.9 -m venv sphinx_3.4.3
	. sphinx_3.4.3/bin/activate
	pip install -r Documentation/sphinx/min_requirements.txt

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@xxxxxxxxxx>
---
 Documentation/doc-guide/sphinx.rst        | 23 +++++++++++++++++++++++
 Documentation/sphinx/min_requirements.txt | 10 ++++++++++
 2 files changed, 33 insertions(+)
 create mode 100644 Documentation/sphinx/min_requirements.txt

diff --git a/Documentation/doc-guide/sphinx.rst b/Documentation/doc-guide/sphinx.rst
index 5a91df105141..607589592bfb 100644
--- a/Documentation/doc-guide/sphinx.rst
+++ b/Documentation/doc-guide/sphinx.rst
@@ -131,6 +131,29 @@ It supports two optional parameters:
 ``--no-virtualenv``
 	Use OS packaging for Sphinx instead of Python virtual environment.
 
+Installing Sphinx Minimal Version
+---------------------------------
+
+When changing Sphinx build system, it is important to ensure that
+the minimal version will still be supported. Nowadays, it is
+becoming harder to do that on modern distributions, as it is not
+possible to install with Python 3.13 and above.
+
+Testing with the lowest supported Python version as defined at
+Documentation/process/changes.rst can be done by creating
+a venv with it with, and install minimal requirements with::
+
+	/usr/bin/python3.9 -m venv sphinx_min
+	. sphinx_min/bin/activate
+	pip install -r Documentation/sphinx/min_requirements.txt
+
+A more comprehensive test can be done by using:
+
+	scripts/test_doc_build.py
+
+Such script create one Python venv per supported version,
+optionally building documentation for a range of Sphinx versions.
+
 
 Sphinx Build
 ============
diff --git a/Documentation/sphinx/min_requirements.txt b/Documentation/sphinx/min_requirements.txt
new file mode 100644
index 000000000000..52d9f27010e8
--- /dev/null
+++ b/Documentation/sphinx/min_requirements.txt
@@ -0,0 +1,10 @@
+alabaster >=0.7,<0.8
+docutils>=0.15,<0.18
+jinja2>=2.3,<3.1
+PyYAML>=5.1,<6.1
+Sphinx==3.4.3
+sphinxcontrib-applehelp==1.0.2
+sphinxcontrib-devhelp==1.0.1
+sphinxcontrib-htmlhelp==1.0.3
+sphinxcontrib-qthelp==1.0.2
+sphinxcontrib-serializinghtml==1.1.4
-- 
2.49.0