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Thu, 19 May 2022 09:13:54 +0000 (GMT) Message-ID: <9666c15f-a824-0c8e-508d-57d1da147fff@linux.ibm.com> Date: Thu, 19 May 2022 11:13:54 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 Subject: Re: [PATCH v4 1/2] drivers/s390/char: Add Ultravisor io device Content-Language: en-US To: Heiko Carstens Cc: Steffen Eiden , Greg KH , Alexander Gordeev , Shuah Khan , Christian Borntraeger , Claudio Imbrenda , David Hildenbrand , Nico Boehr , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, kvm@vger.kernel.org References: <20220510144724.3321985-1-seiden@linux.ibm.com> <20220510144724.3321985-2-seiden@linux.ibm.com> <48550162-0f8c-4b23-dea4-b9060b24eed9@linux.ibm.com> From: Janosch Frank In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: V7QkVM9P7-igVUwVQ4chEEwn1CMV0EG0 X-Proofpoint-GUID: mJriKk9jQArH-1P7CpW_LE3zk6ejvPRs X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.874,Hydra:6.0.486,FMLib:17.11.64.514 definitions=2022-05-19_01,2022-05-19_01,2022-02-23_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 mlxlogscore=967 clxscore=1015 adultscore=0 lowpriorityscore=0 bulkscore=0 priorityscore=1501 malwarescore=0 phishscore=0 impostorscore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2202240000 definitions=main-2205190053 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/19/22 07:37, Heiko Carstens wrote: > On Wed, May 18, 2022 at 03:45:27PM +0200, Janosch Frank wrote: >>>> + 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. > > Why not simply use module_cpu_feature_match() to implement auto module > loading like we do it for the crypto modules? That would require that > either the uv facility is represented within elf hwcaps, or > alternatively the s390 implementation of cpu_feature() needs to be > changed to work with cpu facilities instead of hwcap bits. > (see arch/s390/include/asm/cpufeature.h) > > This doesn't look too difficult. Or was there a reason not to go this route? I'd guess we looked into the wrong direction for auto-load. We'll look into that for 5.20 but we'll take this patch with the "m" tristate for 5.19. Thanks for the pointer and review.