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

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Date:	Mon, 15 Feb 2016 17:05:22 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Arnd Bergmann <arnd@...db.de>
CC:	Andrew Jones <drjones@...hat.com>,
	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>,
	<xen-devel@...ts.xensource.com>, <boris.ostrovsky@...cle.com>
Subject: Re: [PATCH] xen kconfig: clarify INPUT_XEN_KBDDEV_FRONTEND select

On 15/02/16 16:51, Stefano Stabellini wrote:
> CC'ing a few others.
> 
> On Fri, 12 Feb 2016, 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.

I would remove the select.

Existing configurations with both XEN_FBDEV_FRONTEND and
XEN_KBDDEV_FRONTEND will continue to work (since XEN_KBDEV_FRONTEND is
already enabled removing the select won't turn it off).

David

>> 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
> 
> This looks very hackish. Couldn't we just do the following?
> 
> diff --git a/drivers/video/fbdev/Kconfig b/drivers/video/fbdev/Kconfig
> index 8ea45a5..3c15f6d 100644
> --- a/drivers/video/fbdev/Kconfig
> +++ b/drivers/video/fbdev/Kconfig
> @@ -2246,7 +2246,7 @@ config XEN_FBDEV_FRONTEND
>  	select FB_SYS_IMAGEBLIT
>  	select FB_SYS_FOPS
>  	select FB_DEFERRED_IO
> -	select INPUT_XEN_KBDDEV_FRONTEND if INPUT_MISC
> +	select INPUT_XEN_KBDDEV_FRONTEND if (INPUT && INPUT_MISC)
>  	select XEN_XENBUS_FRONTEND
>  	default y
>  	help
>