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

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Message-ID: <alpine.DEB.2.02.1602151708110.27008@kaball.uk.xensource.com>
Date:	Mon, 15 Feb 2016 17:08:30 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	David Vrabel <david.vrabel@...rix.com>
CC:	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Arnd Bergmann <arnd@...db.de>,
	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 Mon, 15 Feb 2016, David Vrabel wrote:
> 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).

I am happy with that too.

 
> >> 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
> > 
>