linux-kernel - Re: [PATCH] drm/i915: Fix Kconfig error for CONFIG_DRM

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Date:   Mon, 14 Aug 2023 10:26:45 +0300
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     Wang Jinchao <wangjinchao@...sion.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Cc:     stone.xulei@...sion.com
Subject: Re: [PATCH] drm/i915: Fix Kconfig error for CONFIG_DRM_I915

On Sat, 12 Aug 2023, Wang Jinchao <wangjinchao@...sion.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
> However, according to Kconfig, CONFIG_DRM_I915 will select
> BACKLIGHT_CLASS_DEVICE only if ACPI is enabled.
> This led to an error, which can be resolved by removing the
> conditional statements related to ACPI.

The real fix is to use

	depends on BACKLIGHT_CLASS_DEVICE || BACKLIGHT_CLASS_DEVICE=n

but in order to do that, you need to change a lot of places to depend
on, not select BACKLIGHT_CLASS_DEVICE, because otherwise you end up with
other dependency issues.

BR,
Jani.

>
> Signed-off-by: Wang Jinchao <wangjinchao@...sion.com>
> ---
>  drivers/gpu/drm/i915/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/Kconfig b/drivers/gpu/drm/i915/Kconfig
> index 01b5a8272a27..5003de921bf7 100644
> --- a/drivers/gpu/drm/i915/Kconfig
> +++ b/drivers/gpu/drm/i915/Kconfig
> @@ -24,7 +24,7 @@ config DRM_I915
>  	select IRQ_WORK
>  	# i915 depends on ACPI_VIDEO when ACPI is enabled
>  	# but for select to work, need to select ACPI_VIDEO's dependencies, ick
> -	select BACKLIGHT_CLASS_DEVICE if ACPI
> +	select BACKLIGHT_CLASS_DEVICE
>  	select INPUT if ACPI
>  	select X86_PLATFORM_DEVICES if ACPI
>  	select ACPI_WMI if ACPI

-- 
Jani Nikula, Intel Open Source Graphics Center