Subject: Re: [PATCH] drivers: depend on instead of select BACKLIGHT_CLASS_DEVICE and ACPI_VIDEO

From: Darren Hart <[email-masked]>
Date: Tue, 21 Oct 2014 13:50:07 -0700

On Sat, Oct 18, 2014 at 12:13:23AM +0300, Jani Nikula wrote:
> Documentation/kbuild/kconfig-language.txt warns to use select with care,
> and in general use select only for non-visible symbols and for symbols
> with no dependencies, because select will force a symbol to a value
> without visiting the dependencies.
> 
> Select has become particularly problematic, interdependently, with the
> BACKLIGHT_CLASS_DEVICE and ACPI_VIDEO configs. For example:
> 
> scripts/kconfig/conf --randconfig Kconfig
> KCONFIG_SEED=0x48312B00
> warning: (DRM_RADEON && DRM_NOUVEAU && DRM_I915 && DRM_GMA500 &&
> DRM_SHMOBILE && DRM_TILCDC && FB_BACKLIGHT && FB_MX3 && USB_APPLEDISPLAY
> && FB_OLPC_DCON && ASUS_LAPTOP && SONY_LAPTOP && THINKPAD_ACPI &&
> EEEPC_LAPTOP && ACPI_CMPC && SAMSUNG_Q10) selects BACKLIGHT_CLASS_DEVICE
> which has unmet direct dependencies (HAS_IOMEM && BACKLIGHT_LCD_SUPPORT)
> warning: (DRM_RADEON && DRM_NOUVEAU && DRM_I915 && DRM_GMA500 &&
> DRM_SHMOBILE && DRM_TILCDC && FB_BACKLIGHT && FB_MX3 && USB_APPLEDISPLAY
> && FB_OLPC_DCON && ASUS_LAPTOP && SONY_LAPTOP && THINKPAD_ACPI &&
> EEEPC_LAPTOP && ACPI_CMPC && SAMSUNG_Q10) selects BACKLIGHT_CLASS_DEVICE
> which has unmet direct dependencies (HAS_IOMEM && BACKLIGHT_LCD_SUPPORT)
> 
> With tristates it's possible to end up selecting FOO=y depending on
> BAR=m in the config, which gets discovered at build time, not config
> time, like reported in the thread referenced below.
> 
> Do the following to fix the dependencies:
> 
> * Depend on instead of select BACKLIGHT_CLASS_DEVICE everywhere. Drop
>   select BACKLIGHT_LCD_SUPPORT in such cases, as it's a dependency of
>   BACKLIGHT_CLASS_DEVICE.
> 
> * Remove config FB_BACKLIGHT altogether, and replace it with a
>   dependency on BACKLIGHT_CLASS_DEVICE. All configs selecting
>   FB_BACKLIGHT select or depend on FB anyway, so we can simplify.
> 
> * Depend on (ACPI && ACPI_VIDEO) || ACPI=n in several places instead of
>   selecting ACPI_VIDEO and a number of its dependencies if ACPI is
>   enabled. This is tied to backlight, as ACPI_VIDEO depends on
>   BACKLIGHT_CLASS_DEVICE.
> 
> * Replace a couple of select INPUT/VT with depends as it seemed to be
>   necessary.
> 
> Reference: http://lkml.kernel.org/r/[email-masked]
> Reported-by: Jim Davis <[email-masked]>
> Cc: Randy Dunlap <[email-masked]>
> Cc: David Airlie <[email-masked]>
> Cc: Daniel Vetter <[email-masked]>
> Cc: Greg Kroah-Hartman <[email-masked]>
> Cc: Darren Hart <[email-masked]>
> Cc: Laurent Pinchart <[email-masked]>
> Cc: Benjamin Herrenschmidt <[email-masked]>
> Cc: Jens Frederich <[email-masked]>
> Cc: Daniel Drake <[email-masked]>
> Cc: Jon Nettleton <[email-masked]>
> Cc: Jean-Christophe Plagniol-Villard <[email-masked]>
> Cc: Tomi Valkeinen <[email-masked]>
> Signed-off-by: Jani Nikula <[email-masked]>

As for the drivers/platform/x86/Kconfig:

Acked-by: Darren Hart <[email-masked]>

Thanks,

-- 
Darren Hart
Intel Open Source Technology Center