diff mbox

xen kconfig: clarify INPUT_XEN_KBDDEV_FRONTEND select

Message ID alpine.DEB.2.02.1602151643150.27008@kaball.uk.xensource.com (mailing list archive)
State New, archived
Headers show

Commit Message

Stefano Stabellini Feb. 15, 2016, 4:51 p.m. UTC
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.
> 
> Signed-off-by: Arnd Bergmann <arnd@arndb.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?

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Comments

David Vrabel Feb. 15, 2016, 5:05 p.m. UTC | #1
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@arndb.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
> 

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Stefano Stabellini Feb. 15, 2016, 5:08 p.m. UTC | #2
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@arndb.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
> > 
> 
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Arnd Bergmann Feb. 16, 2016, 11:35 a.m. UTC | #3
On Monday 15 February 2016 16:51:08 Stefano Stabellini wrote:
> > 
> > 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
> 

No, that doesn't solve the problem:

If XEN_FBDEV_FRONTEND=y, INPUT=m and INPUT_MISC=y, we would still
get INPUT_XEN_KBDDEV_FRONTEND=y, which cannot work because of INPUT=m.

INPUT_MISC already depends on INPUT, so your change has no effect
at all.

	Arnd
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diff mbox

Patch

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