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

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Message-ID: <7d87d5c9-2d16-7574-3c08-04dbfb58d943@linux.ibm.com>
Date:   Wed, 18 May 2022 15:49:57 +0200
From:   Steffen Eiden <seiden@...ux.ibm.com>
To:     Janosch Frank <frankja@...ux.ibm.com>,
        Heiko Carstens <hca@...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>,
        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 5/18/22 15:45, Janosch Frank wrote:
> On 5/18/22 13:47, Heiko Carstens wrote:
>> 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.
> 
> There was a lot of discussion around this already and the "Y" was chosen 
> as auto-loading this is a pain and therefore the SCLP and CHSC-Misc set 
> it to Y and we took that as an example (Steffen spoke to Peter to get 
> guidance).
> 
> I'm sure that we want the possibility to have this as a module. 
> Personally I'd choose "m" over "y" since the module is only useful for a 
> very small amount of users.

I am fine with changing "y" to "m".

Steffen