scripts: sphinx-pre-install: change the warning for version < 2.4.4

As requested by Jon, change the version check, in order to not
emit a warning if version is >= 1.7.9, but below 2.4.4.

After this patch, if someone used an older version, it will
say:

	./scripts/sphinx-pre-install
	Sphinx version 1.7.9
	Note: It is recommended at least Sphinx version 2.4.4 if you need PDF support.
	Detected OS: Fedora release 31 (Thirty One).

	To upgrade Sphinx, use:

		/devel/v4l/docs/sphinx_1.7.9/bin/python3 -m venv sphinx_2.4.4
		. sphinx_2.4.4/bin/activate
		pip install -r ./Documentation/sphinx/requirements.txt

	If you want to exit the virtualenv, you can use:
		deactivate

	All optional dependencies are met.
	Needed package dependencies are met.

If Sphinx is not detected at all, it
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/79584d317ba16f5d4f37801c5ee57cf04085f962.1587478901.git.mchehab+huawei@kernel.orgSigned-off-by: Jonathan Corbet <corbet@lwn.net>

scripts/sphinx-pre-install

@@ -29,6 +29,8 @@ my $install = "";
 my $virtenv_dir = "";
 my $python_cmd = "";
 my $min_version;
+my $rec_version = "1.7.9";	# PDF won't build here
+my $min_pdf_version = "2.4.4";	# Min version where pdf builds
 
 #
 # Command line arguments
@@ -254,7 +256,7 @@ sub get_sphinx_version($)
 
 sub check_sphinx()
 {
-	my $rec_version;
+	my $default_version;
 	my $cur_version;
 
 	open IN, $conf or die "Can't open $conf";
@@ -271,15 +273,15 @@ sub check_sphinx()
 	open IN, $requirement_file or die "Can't open $requirement_file";
 	while (<IN>) {
 		if (m/^\s*Sphinx\s*==\s*([\d\.]+)$/) {
-			$rec_version=$1;
+			$default_version=$1;
 			last;
 		}
 	}
 	close IN;
 
-	die "Can't get recommended sphinx version from $requirement_file" if (!$min_version);
+	die "Can't get default sphinx version from $requirement_file" if (!$default_version);
 
-	$virtenv_dir = $virtenv_prefix . $rec_version;
+	$virtenv_dir = $virtenv_prefix . $default_version;
 
 	my $sphinx = get_sphinx_fname();
 	if ($sphinx eq "") {
@@ -294,7 +296,7 @@ sub check_sphinx()
 
 	if ($cur_version lt $min_version) {
 		printf "ERROR: Sphinx version is %s. It should be >= %s (recommended >= %s)\n",
-		       $cur_version, $min_version, $rec_version;;
+		       $cur_version, $min_version, $default_version;
 		$need_sphinx = 1;
 		return;
 	}
@@ -302,6 +304,13 @@ sub check_sphinx()
 	if ($cur_version lt $rec_version) {
 		printf "Sphinx version %s\n", $cur_version;
 		print "Warning: It is recommended at least Sphinx version $rec_version.\n";
+		print "         If you want pdf, you need at least $min_pdf_version.\n";
+		$rec_sphinx_upgrade = 1;
+		return;
+	}
+	if ($cur_version lt $min_pdf_version) {
+		printf "Sphinx version %s\n", $cur_version;
+		print "Note: It is recommended at least Sphinx version $min_pdf_version if you need PDF support.\n";
 		$rec_sphinx_upgrade = 1;
 		return;
 	}