On Sun, 20 Aug 2023, Wang Jinchao <wangjinchao@xxxxxxxxxxx> wrote: > 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. I told you in [1] what the real fix is. The IS_REACHABLE() solution has been suggested a number of times, but I think it's creating an unexpected and silent failure configuration. I think IS_REACHABLE() is the wrong thing to do in most cases. BR, Jani. [1] https://lore.kernel.org/r/87o7jaythm.fsf@xxxxxxxxx > > Signed-off-by: Wang Jinchao <wangjinchao@xxxxxxxxxxx> > --- > 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 */ -- Jani Nikula, Intel Open Source Graphics Center
