linux-kernel - Re: [PATCH] drivers: depend on instead of select BACKLIGHT_CLASS_DEVICE and ACPI

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Date:	Tue, 21 Oct 2014 13:50:07 -0700
From:	Darren Hart <dvhart@...radead.org>
To:	Jani Nikula <jani.nikula@...el.com>
Cc:	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	linuxppc-dev@...ts.ozlabs.org, platform-driver-x86@...r.kernel.org,
	linux-usb@...r.kernel.org, linux-fbdev@...r.kernel.org,
	Randy Dunlap <rdunlap@...radead.org>,
	David Airlie <airlied@...ux.ie>,
	Daniel Vetter <daniel.vetter@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Jens Frederich <jfrederich@...il.com>,
	Daniel Drake <dsd@...top.org>,
	Jon Nettleton <jon.nettleton@...il.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Tomi Valkeinen <tomi.valkeinen@...com>
Subject: Re: [PATCH] drivers: depend on instead of select
 BACKLIGHT_CLASS_DEVICE and ACPI_VIDEO

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/CA+r1ZhhmT4DrWtf6MbRQo5EqXwx+LxCqh15Vsu_d9WpftLhnxw@mail.gmail.com
> Reported-by: Jim Davis <jim.epost@...il.com>
> Cc: Randy Dunlap <rdunlap@...radead.org>
> Cc: David Airlie <airlied@...ux.ie>
> Cc: Daniel Vetter <daniel.vetter@...el.com>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Darren Hart <dvhart@...radead.org>
> Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Jens Frederich <jfrederich@...il.com>
> Cc: Daniel Drake <dsd@...top.org>
> Cc: Jon Nettleton <jon.nettleton@...il.com>
> Cc: Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>
> Cc: Tomi Valkeinen <tomi.valkeinen@...com>
> Signed-off-by: Jani Nikula <jani.nikula@...el.com>

As for the drivers/platform/x86/Kconfig:

Acked-by: Darren Hart <dvhart@...ux.intel.com>

Thanks,

-- 
Darren Hart
Intel Open Source Technology Center
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