helios4: workaround fancontrol for mvebu >=6.18 (no J17 timer patch)

J17 PWM on Helios4 depends on the out-of-tree timer-assignment patch, which
is currently .disabled from mvebu-6.18 onwards while it's ported to the
refactored pwm chip API. Without the patch, /dev/fan-j17/pwm1 does not
appear and fancontrol.service aborts on start.

Add a post_family_tweaks_bsp hook in the helios4 board config that comments
out the J17 references in /etc/fancontrol when KERNEL_MAJOR_MINOR >= 6.18
(via linux-version compare), keeping the original line as a commented
reference so the file also serves as documentation of the historical config.
Drop this hook once the patch is ported.

Author: iav

config/boards/helios4.conf

@@ -20,3 +20,23 @@ function post_family_config__helios4_extra_packages() {
 	add_packages_to_image "fancontrol"
 	add_packages_to_image "ethtool"
 }
+
+# J17 PWM on Helios4 depends on the out-of-tree timer-assignment patch, which
+# is currently .disabled from mvebu-6.18 onwards (needs porting to the
+# refactored pwm chip API). Comment out original J17 references in
+# /etc/fancontrol so the service starts with J10-only; drop this hook once
+# the patch is ported and re-enabled.
+function post_family_tweaks_bsp__helios4_j17_disable_until_patch_ported() {
+	linux-version compare "${KERNEL_MAJOR_MINOR}" ge 6.18 || return 0
+	[[ -s "${destination}/etc/fancontrol" ]] || return 0
+	display_alert "${BOARD}" "fancontrol: commenting out J17 (no >=6.18 timer patch)" "info"
+	awk '
+		BEGIN { print "# J17 PWM disabled: mvebu >=6.18 lacks the timer-assignment patch." }
+		/\/dev\/fan-j17\/pwm1/ {
+			print "# " $0
+			gsub(/ ?\/dev\/fan-j17\/pwm1=[^ ]+/, "")
+		}
+		{ print }
+	' "${destination}/etc/fancontrol" > "${destination}/etc/fancontrol.new"
+	mv "${destination}/etc/fancontrol.new" "${destination}/etc/fancontrol"
+}