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Thu, 4 Dec 2025 13:09:04 GMT Received: from smtpav06.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 7173F5805D; Thu, 4 Dec 2025 13:09:04 +0000 (GMT) Received: from smtpav06.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id EF01258055; Thu, 4 Dec 2025 13:09:01 +0000 (GMT) Received: from [9.111.38.114] (unknown [9.111.38.114]) by smtpav06.dal12v.mail.ibm.com (Postfix) with ESMTP; Thu, 4 Dec 2025 13:09:01 +0000 (GMT) Message-ID: Subject: Re: [PATCH v3] PCI: s390: Expose the UID as an arch specific PCI slot attribute From: Niklas Schnelle To: Gerd Bayer , Bjorn Helgaas , Lukas Wunner Cc: Gerald Schaefer , Christian Borntraeger , Matthew Rosato , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Sven Schnelle , Julian Ruess , Peter Oberparleiter , Ramesh Errabolu , linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org Date: Thu, 04 Dec 2025 14:09:01 +0100 In-Reply-To: References: <20251015-uid_slot-v3-1-44389895c1bb@linux.ibm.com> Autocrypt: addr=schnelle@linux.ibm.com; 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charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.58.2 (3.58.2-1.fc43) Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: dLYNHFuJPZXyohLucuu6DGpz4VqXPQss X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMTI5MDAwOCBTYWx0ZWRfX+lwHBp/btG+m FeAbPsngqQx/K5HC52q1sO0r1osqeLnIgeEXv8qUlTo5mF05MoZ1IrAdYSsYdwqGY2ArvRJofwU Wl2qe/GbCu4CTJz7QOox48PTKZSbj3RZLyAf72VXx9386CcgfrOcWqaRZ9V097FeOuGcY/NXwPp NrUc/nJBA2/OpZSL7QZmTbAl7LSnn7iLYJSc/RQuJ5aCMSs+ULaiXNnfPeSmHhDUx29Lhz1CPNo P9hHPZrYEJPY+EsEqZAnyS0AZ5iSqSuckFFHeXsVkYFNdXDP2sphmeGQv/BKw160Amla/yZZlzP lETBBW4oICL/dRCqfMlf0n+HJaD3UrqLP95noz8hZt/IzMK5c/e9+w+Nf0Qr0RDrfWIQ1ZQOp3T OaO9t+AqKJyCcX8OAjb5HDBw3uu3EA== X-Authority-Analysis: v=2.4 cv=Scz6t/Ru c=1 sm=1 tr=0 ts=693187f2 cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=IkcTkHD0fZMA:10 a=wP3pNCr1ah4A:10 a=VkNPw1HP01LnGYTKEx00:22 a=VnNF1IyMAAAA:8 a=loEuMJwbk0X0rLMOwskA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: BnPuDKurt7NUTjmKWVxx4Lwvi3YXCcFt X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2025-12-04_03,2025-12-03_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 phishscore=0 bulkscore=0 lowpriorityscore=0 adultscore=0 clxscore=1015 spamscore=0 impostorscore=0 priorityscore=1501 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2510240000 definitions=main-2511290008 On Thu, 2025-12-04 at 13:45 +0100, Gerd Bayer wrote: > On Wed, 2025-10-15 at 15:42 +0200, Niklas Schnelle wrote: > > On s390, an individual PCI function can generally be identified by two > > identifiers, the FID and the UID. Which identifier is used depends on > > the scope and the platform configuration. > >=20 > > The first identifier, the FID, is always available and identifies a PCI > > device uniquely within a machine. The FID may be virtualized by > > hypervisors, but on the LPAR level, the machine scope makes it > > impossible to create the same configuration based on FIDs on two > > different LPARs of the same machine, and difficult to reuse across > > machines. > >=20 > > Such matching LPAR configurations are useful, though, allowing > > standardized setups and booting a Linux installation on different LPARs= . > > To this end the UID, or user-defined identifier, was introduced. While > > it is only guaranteed to be unique within an LPAR and only if indicated > > by firmware, it allows users to replicate PCI device setups. > >=20 > > On s390, which uses a machine hypervisor, a per PCI function hotplug > > model is used. The shortcoming with the UID then is, that it is not > > visible to the user without first attaching the PCI function and > > accessing the "uid" device attribute. The FID, on the other hand, is > > used as the slot name and is thus known even with the PCI function in > > standby. > >=20 > > Remedy this shortcoming by providing the UID as an attribute on the slo= t > > allowing the user to identify a PCI function based on the UID without > > having to first attach it. Do this via a macro mechanism analogous to > > what was introduced by commit 265baca69a07 ("s390/pci: Stop usurping > > pdev->dev.groups") for the PCI device attributes. >=20 > Hi Niklas, >=20 > I like this addition a lot. Also, Lukas' method to add arch-specific > attributes to sysfs. Is there a reason why you didn't apply that > mechanism 1-to-1? I considered that and actually had basically the same as your diff in an intermediate version. To me it looked cleaner with the #ifdef in the attribute_group array initialization as I feel that it is more obvious if the macroed elements are used. This may be because my editor grays out the code between unused #ifdef or just because "it's in one place" either way just a matter of taste. Also the comma gave me checkpatch complaints. >=20 > >=20 > > Signed-off-by: Niklas Schnelle > > --- > > Note: I considered adding the UID as a generic "index" via the hotplug > > slot driver but felt like there is probably too little commonality on > > format and usage patterns >=20 > Sorry for my ignorance but how is the hotplug slot driver defining an > "index" or how is used? >=20 It's not. I meant that I considered that the UID could be turned into a generic "index" attribute in the same way that the UID is used as /sys/bus/pci/devices//index on s390 while the same attribute is an SMBIOS index thing on x86 and others.