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

[Jani Nikula <jani.nikula@linux.intel.com>]

On Sun, 20 Aug 2023, Wang Jinchao <wangjinchao@xfusion.com> 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@intel.com


>
> 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 */

-- 
Jani Nikula, Intel Open Source Graphics Center