tests: mockup: add a comment explaining the kernel version definition

The library only works on newer kernels. The specific features we're
using have only available since linux v5.1.0. Add a comment explaining
this limitation to the library code.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

diff --git a/tests/mockup/gpio-mockup.c b/tests/mockup/gpio-mockup.c
index b2dc7e1739f2b0a178b43e428af0f795a2b00717..c7a31525b6563e9ccccbd929f8ede95d5627998c 100644 (file)
--- a/tests/mockup/gpio-mockup.c
+++ b/tests/mockup/gpio-mockup.c
@@ -19,6 +19,10 @@
 #include "gpio-mockup.h"
 
 #define EXPORT                 __attribute__((visibility("default")))
+/*
+ * The gpio-mockup features (including the debugfs interface) we're using
+ * in this library have first been released in the linux kernel version below.
+ */
 #define MIN_KERNEL_VERSION     KERNEL_VERSION(5, 1, 0)
 
 struct gpio_mockup_chip {