linux-kernel - Re: [PATCH] xen kconfig: clarify INPUT_XEN_KBDDEV

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Date:	Fri, 12 Feb 2016 14:56:45 +0100
From:	Andrew Jones <drjones@...hat.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	linux-arm-kernel@...ts.infradead.org,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xen kconfig: clarify INPUT_XEN_KBDDEV_FRONTEND select

On Fri, Feb 12, 2016 at 01:04:40PM +0100, Arnd Bergmann wrote:
> The Xen framebuffer driver selects the xen keyboard driver, so the latter
> will be built-in if XEN_FBDEV_FRONTEND=y. However, when CONFIG_INPUT
> is a loadable module, this configuration cannot work. On mainline kernels,
> the symbol will be enabled but not used, while in combination with
> a patch I have to detect such useless configurations, we get the
> expected link failure:
> 
> drivers/input/built-in.o: In function `xenkbd_remove':
> xen-kbdfront.c:(.text+0x2f0): undefined reference to `input_unregister_device'
> xen-kbdfront.c:(.text+0x30e): undefined reference to `input_unregister_device'
> 
> This changes the dependencies of XEN_FBDEV_FRONTEND so it cannot be
> built-in if CONFIG_INPUT=m && CONFIG_INPUT_MISC=y, as that would result
> in the broken select.
> 
> As usual, we would be much better off without the 'select', but removing
> it now would likely break existing user configurations that depend on
> it, so this adds another hack on top to get it working.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> Fixes: 36c1132e34bd ("xen kconfig: fix select INPUT_XEN_KBDDEV_FRONTEND")
> ---
>  drivers/video/fbdev/Kconfig | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/video/fbdev/Kconfig b/drivers/video/fbdev/Kconfig
> index 8ea45a5cd806..fd3d6fd290a9 100644
> --- a/drivers/video/fbdev/Kconfig
> +++ b/drivers/video/fbdev/Kconfig
> @@ -2241,6 +2241,7 @@ config FB_VIRTUAL
>  config XEN_FBDEV_FRONTEND
>  	tristate "Xen virtual frame buffer support"
>  	depends on FB && XEN
> +	depends on INPUT || !INPUT_MISC
>  	select FB_SYS_FILLRECT
>  	select FB_SYS_COPYAREA
>  	select FB_SYS_IMAGEBLIT
> -- 
> 2.7.0
>

Reviewed-by: Andrew Jones <drjones@...hat.com>

Thanks,
drew