[Intel-gfx] [PATCH v3] drm/i915: Fix Kconfig error for CONFIG_DRM_I915

[Wang Jinchao <wangjinchao@xfusion.com>]

When CONFIG_DRM_I915 is set to 'y' and CONFIG_BACKLIGHT_CLASS_DEVICE
is set to 'm', we encountered an ld.lld error during the build process:

	ld.lld: error: undefined symbol: backlight_device_get_by_name
	>>> referenced by intel_backlight.c:955
	>>>               vmlinux.o:(intel_backlight_device_register)

	ld.lld: error: undefined symbol: backlight_device_register
	>>> referenced by intel_backlight.c:971
	>>>               vmlinux.o:(intel_backlight_device_register)

	ld.lld: error: undefined symbol: backlight_device_unregister
	>>> referenced by intel_backlight.c:999
	>>>               vmlinux.o:(intel_backlight_device_unregister)

This issue occurred because intel_backlight_device_register and
intel_backlight_device_unregister were enclosed within
\#if IS_ENABLED(CONFIG_BACKLIGHT_CLASS_DEVICE) and #endif directives.
However, according to Kconfig, CONFIG_DRM_I915 will select
BACKLIGHT_CLASS_DEVICE only if ACPI is enabled.
This led to an error when ACPI is not enabled.
Change IS_ENABLED to IS_REACHABLE and use IS_REACHABLE to encompass
the implementation of intel_connector_register() to solve this issue.

Signed-off-by: Wang Jinchao <wangjinchao@xfusion.com>
---
 drivers/gpu/drm/i915/display/intel_backlight.c | 2 +-
 drivers/gpu/drm/i915/display/intel_backlight.h | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_backlight.c b/drivers/gpu/drm/i915/display/intel_backlight.c
index 2e8f17c04522..d812cdc74a84 100644
--- a/drivers/gpu/drm/i915/display/intel_backlight.c
+++ b/drivers/gpu/drm/i915/display/intel_backlight.c
@@ -795,7 +795,7 @@ void intel_backlight_enable(const struct intel_crtc_state *crtc_state,
 	mutex_unlock(&i915->display.backlight.lock);
 }
 
-#if IS_ENABLED(CONFIG_BACKLIGHT_CLASS_DEVICE)
+#if IS_REACHABLE(CONFIG_BACKLIGHT_CLASS_DEVICE)
 static u32 intel_panel_get_backlight(struct intel_connector *connector)
 {
 	struct drm_i915_private *i915 = to_i915(connector->base.dev);
diff --git a/drivers/gpu/drm/i915/display/intel_backlight.h b/drivers/gpu/drm/i915/display/intel_backlight.h
index 339643f63897..207fe1c613d8 100644
--- a/drivers/gpu/drm/i915/display/intel_backlight.h
+++ b/drivers/gpu/drm/i915/display/intel_backlight.h
@@ -36,7 +36,7 @@ u32 intel_backlight_invert_pwm_level(struct intel_connector *connector, u32 leve
 u32 intel_backlight_level_to_pwm(struct intel_connector *connector, u32 level);
 u32 intel_backlight_level_from_pwm(struct intel_connector *connector, u32 val);
 
-#if IS_ENABLED(CONFIG_BACKLIGHT_CLASS_DEVICE)
+#if IS_REACHABLE(CONFIG_BACKLIGHT_CLASS_DEVICE)
 int intel_backlight_device_register(struct intel_connector *connector);
 void intel_backlight_device_unregister(struct intel_connector *connector);
 #else /* CONFIG_BACKLIGHT_CLASS_DEVICE */
-- 
2.40.0