linux-kernel - Re: [PATCH v4 1/2] drivers/s390/char: Add Ultravisor io device

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Date:   Wed, 18 May 2022 13:47:18 +0200
From:   Heiko Carstens <hca@...ux.ibm.com>
To:     Steffen Eiden <seiden@...ux.ibm.com>
Cc:     Greg KH <greg@...ah.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Shuah Khan <shuah@...nel.org>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Nico Boehr <nrb@...ux.ibm.com>, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v4 1/2] drivers/s390/char: Add Ultravisor io device

On Tue, May 10, 2022 at 02:47:23PM +0000, Steffen Eiden wrote:
> diff --git a/drivers/s390/char/Kconfig b/drivers/s390/char/Kconfig
> index 6cc4b19acf85..e9b9902abbaf 100644
> --- a/drivers/s390/char/Kconfig
> +++ b/drivers/s390/char/Kconfig
> @@ -100,6 +100,16 @@ config SCLP_OFB
>  	  This option enables the Open-for-Business interface to the s390
>  	  Service Element.
>  
> +config S390_UV_UAPI
> +	def_tristate y
> +	prompt "Ultravisor userspace API"
> +	help
> +	  Selecting exposes parts of the UV interface to userspace
> +	  by providing a misc character device at /dev/uv.
> +	  Using IOCTLs one can interact with the UV.
> +	  The device is only available if the Ultravisor
> +	  Facility (158) is present.

Is there a reason why this is default "y"? If you think this should be
compiled into the kernel if used, then why allow to make it a module
at all?
Instead you could get rid of a couple if lines of code.