Building HID generic with LampArray support enabled caused link
failures when LEDS_CLASS_MULTICOLOR was disabled, due to unresolved
led_classdev_multicolor_* and led_mc_* symbols.

hid-lamparray.o was built whenever HID_GENERIC was enabled,
regardless of LED multicolor support.

Introduce CONFIG_HID_LAMPARRAY with dependencies on HID_GENERIC &&
LEDS_CLASS && LEDS_CLASS_MULTICOLOR and build hid-lamparray.o only
when enabled. Provide stub helpers so hid-generic.c builds cleanly
when the option is disabled.

Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/oe-kbuild-all/202602200233.9Bwav9tZ-lkp@intel.com/
Link: https://lore.kernel.org/oe-kbuild-all/202602200241.6ypuWvE5-lkp@intel.com/
Link: https://lore.kernel.org/oe-kbuild-all/202602192025.xrvVo680-lkp@intel.com/
Link: https://lore.kernel.org/oe-kbuild-all/202602192131.Q9y8Kqvt-lkp@intel.com/

Changes in v2:
  - Add CONFIG_HID_LAMPARRAY with proper dependencies
  - Build hid-lamparray.o only when enabled
  - Add stub helpers when disabled
  - Fix build failures reported by kernel test robot

Signed-off-by: Tim Guttzeit <tgu@tuxedocomputers.com>
---
 drivers/hid/Kconfig         | 10 ++++++++++
 drivers/hid/Makefile        |  3 ++-
 drivers/hid/hid-generic.c   |  4 ++--
 drivers/hid/hid-lamparray.h | 25 ++++++++++++++++++++++++-
 4 files changed, 38 insertions(+), 4 deletions(-)

diff --git a/drivers/hid/Kconfig b/drivers/hid/Kconfig
index 920a64b66b25..91547dfa5661 100644
--- a/drivers/hid/Kconfig
+++ b/drivers/hid/Kconfig
@@ -92,6 +92,16 @@ config HID_GENERIC
 
 	If unsure, say Y.
 
+config HID_LAMPARRAY
+	bool "HID LampArray helper"
+	depends on HID_GENERIC && LEDS_CLASS && LEDS_CLASS_MULTICOLOR
+	default y
+	help
+	Helper for HID devices exposing a Lighting/LampArray collection.
+	Treats LampArray devices as a single-zone device and exposes a sysfs
+	interface for changing color and intensity values. Also exposes a
+	sysfs flag to be disabled e.g. by a userspace driver.
+
 config HID_HAPTIC
 	bool "Haptic touchpad support"
 	default n
diff --git a/drivers/hid/Makefile b/drivers/hid/Makefile
index e6903be9c4df..5a14b4b0970d 100644
--- a/drivers/hid/Makefile
+++ b/drivers/hid/Makefile
@@ -12,7 +12,8 @@ obj-$(CONFIG_HID)		+= hid.o
 obj-$(CONFIG_UHID)		+= uhid.o
 
 obj-$(CONFIG_HID_GENERIC)	+= hid-generic.o
-obj-$(CONFIG_HID_GENERIC)	+= hid-lamparray.o
+
+obj-$(CONFIG_HID_LAMPARRAY) += hid-lamparray.o
 
 hid-$(CONFIG_HIDRAW)		+= hidraw.o
 
diff --git a/drivers/hid/hid-generic.c b/drivers/hid/hid-generic.c
index 650c2121b403..57b81c86982c 100644
--- a/drivers/hid/hid-generic.c
+++ b/drivers/hid/hid-generic.c
@@ -77,7 +77,7 @@ static int hid_generic_probe(struct hid_device *hdev,
 	 * Optional: attach LampArray support if present.
 	 * Never fail probe on LampArray errors; keep device functional.
 	 */
-	if (lamparray_is_supported_device(hdev)) {
+	if (IS_ENABLED(CONFIG_HID_LAMPARRAY) && lamparray_is_supported_device(hdev)) {
 		const struct lamparray_init_state init = {
 			.r = 0xff,
 			.g = 0xff,
@@ -108,7 +108,7 @@ static void hid_generic_remove(struct hid_device *hdev)
 {
 	struct lamparray *la = hid_get_drvdata(hdev);
 
-	if (la)
+	if (IS_ENABLED(CONFIG_HID_LAMPARRAY) && la)
 		lamparray_unregister(la);
 
 	hid_hw_stop(hdev);
diff --git a/drivers/hid/hid-lamparray.h b/drivers/hid/hid-lamparray.h
index b786ca00c404..ac3edd366a5b 100644
--- a/drivers/hid/hid-lamparray.h
+++ b/drivers/hid/hid-lamparray.h
@@ -6,6 +6,7 @@
 #include <linux/types.h>
 #include <linux/leds.h>
 #include <linux/err.h>
+#include <linux/errno.h>
 
 struct hid_device;
 struct lamparray;
@@ -21,6 +22,8 @@ struct lamparray_init_state {
 	enum led_brightness brightness;
 };
 
+#if IS_ENABLED(CONFIG_HID_LAMPARRAY)
+
 /**
  * lamparray_is_supported_device() - check whether a HID device supports LampArray
  * @hdev: HID device to inspect
@@ -65,4 +68,24 @@ struct lamparray *lamparray_register(struct hid_device *hdev,
  */
 void lamparray_unregister(struct lamparray *la);
 
-#endif
+#else /* !CONFIG_HID_LAMPARRAY */
+
+static inline bool lamparray_is_supported_device(struct hid_device *hdev)
+{
+	return false;
+}
+
+static inline struct lamparray *
+lamparray_register(struct hid_device *hdev,
+		   const struct lamparray_init_state *led_init_state)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
+
+static inline void lamparray_unregister(struct lamparray *la)
+{
+}
+
+#endif /* CONFIG_HID_LAMPARRAY */
+
+#endif /* _HID_LAMPARRAY_H */
-- 
2.43.0