[{"id":3673237,"web_url":"http://patchwork.ozlabs.org/comment/3673237/","msgid":"","list_archive_url":null,"date":"2026-04-03T17:19:59","subject":"Re: [PATCH v6 2/2] PCI: s390: Expose the UID as an arch specific PCI\n slot attribute","submitter":{"id":73785,"url":"http://patchwork.ozlabs.org/api/people/73785/","name":"Farhan Ali","email":"alifm@linux.ibm.com"},"content":"On 4/2/2026 1:34 PM, Niklas Schnelle wrote:\n> On s390, an individual PCI function can generally be identified by two\n> identifiers, the FID and the UID. Which identifier is used depends on\n> the scope and the platform configuration.\n>\n> The first identifier, the FID, is always available and identifies a PCI\n> device uniquely within a machine. The FID may be virtualized by\n> hypervisors, but on the LPAR level, the machine scope makes it\n> impossible to create the same configuration based on FIDs on two\n> different LPARs of the same machine, and difficult to reuse across\n> machines.\n>\n> Such matching LPAR configurations are useful, though, allowing\n> standardized setups and booting a Linux installation on different LPARs.\n> To this end the UID, or user-defined identifier, was introduced. While\n> it is only guaranteed to be unique within an LPAR and only if indicated\n> by firmware, it allows users to replicate PCI device setups.\n>\n> On s390, which uses a machine hypervisor, a per PCI function hotplug\n> model is used. The shortcoming with the UID then is, that it is not\n> visible to the user without first attaching the PCI function and\n> accessing the \"uid\" device attribute. The FID, on the other hand, is\n> used as the slot name and is thus known even with the PCI function in\n> standby.\n>\n> Remedy this shortcoming by providing the UID as an attribute on the slot\n> allowing the user to identify a PCI function based on the UID without\n> having to first attach it. Do this via a macro mechanism analogous to\n> what was introduced by commit 265baca69a07 (\"s390/pci: Stop usurping\n> pdev->dev.groups\") for the PCI device attributes.\n>\n> Reviewed-by: Gerd Bayer \n> Reviewed-by: Julian Ruess \n> Signed-off-by: Niklas Schnelle \n> ---\n> Documentation/arch/s390/pci.rst | 7 +++++++\n> arch/s390/include/asm/pci.h | 4 ++++\n> arch/s390/pci/pci_sysfs.c | 20 ++++++++++++++++++++\n> drivers/pci/slot.c | 13 ++++++++++++-\n> 4 files changed, 43 insertions(+), 1 deletion(-)\n>\n> diff --git a/Documentation/arch/s390/pci.rst b/Documentation/arch/s390/pci.rst\n> index 31c24ed5506f1fc07f89821f67a814118514f441..4c0f35c8a5588eee3cf0d596e0057f24b3ed079c 100644\n> --- a/Documentation/arch/s390/pci.rst\n> +++ b/Documentation/arch/s390/pci.rst\n> @@ -57,6 +57,13 @@ Entries specific to zPCI functions and entries that hold zPCI information.\n> \n> - /sys/bus/pci/slots/XXXXXXXX/power\n> \n> + In addition to using the FID as the name of the slot the slot directory\n> + also contains the following s390 specific slot attributes.\n> +\n> + - uid:\n> + The User-defined identifier (UID) of the function which may be configured\n> + by this slot. See also the corresponding attribute of the device.\n> +\n> A physical function that currently supports a virtual function cannot be\n> powered off until all virtual functions are removed with:\n> echo 0 > /sys/bus/pci/devices/DDDD:BB:dd.f/sriov_numvf\n> diff --git a/arch/s390/include/asm/pci.h b/arch/s390/include/asm/pci.h\n> index c0ff19dab5807c7e1aabb48a0e9436aac45ec97d..5dcf35f0f325f5f44b28109a1c8d9aef18401035 100644\n> --- a/arch/s390/include/asm/pci.h\n> +++ b/arch/s390/include/asm/pci.h\n> @@ -208,6 +208,10 @@ extern const struct attribute_group zpci_ident_attr_group;\n> \t\t\t &pfip_attr_group,\t\t \\\n> \t\t\t &zpci_ident_attr_group,\n> \n> +extern const struct attribute_group zpci_slot_attr_group;\n> +\n> +#define ARCH_PCI_SLOT_GROUPS (&zpci_slot_attr_group)\n> +\n> extern unsigned int s390_pci_force_floating __initdata;\n> extern unsigned int s390_pci_no_rid;\n> \n> diff --git a/arch/s390/pci/pci_sysfs.c b/arch/s390/pci/pci_sysfs.c\n> index c2444a23e26c4218832bb91930b5f0ffd498d28f..d98d97df792adb3c7e415a8d374cc2f3a65fbb52 100644\n> --- a/arch/s390/pci/pci_sysfs.c\n> +++ b/arch/s390/pci/pci_sysfs.c\n> @@ -187,6 +187,17 @@ static ssize_t index_show(struct device *dev,\n> }\n> static DEVICE_ATTR_RO(index);\n> \n> +static ssize_t zpci_uid_slot_show(struct pci_slot *slot, char *buf)\n> +{\n> +\tstruct zpci_dev *zdev = container_of(slot->hotplug, struct zpci_dev,\n> +\t\t\t\t\t hotplug_slot);\n> +\n> +\treturn sysfs_emit(buf, \"0x%x\\n\", zdev->uid);\n> +}\n\nI think the way we assign the same pci slot to multifunctions (PF and VF \non the same LPAR), IIUC we could possibly display the wrong uid here. I \nam hoping my patch [1] can fix this. I am curious, is there any \ns390-tool that would use the uid? Though this would only impact the NETD \ndevices on newer machines, so I don't know if we want to gate this \nbehind my patch?\n\n[1] https://lore.kernel.org/all/20260330174011.1161-2-alifm@linux.ibm.com/\n\nThanks\n\nFarhan\n\n> +\n> +static struct pci_slot_attribute zpci_slot_attr_uid =\n> +\t__ATTR(uid, 0444, zpci_uid_slot_show, NULL);\n> +\n> static umode_t zpci_index_is_visible(struct kobject *kobj,\n> \t\t\t\t struct attribute *attr, int n)\n> {\n> @@ -243,6 +254,15 @@ const struct attribute_group pfip_attr_group = {\n> \t.attrs = pfip_attrs,\n> };\n> \n> +static struct attribute *zpci_slot_attrs[] = {\n> +\t&zpci_slot_attr_uid.attr,\n> +\tNULL,\n> +};\n> +\n> +const struct attribute_group zpci_slot_attr_group = {\n> +\t.attrs = zpci_slot_attrs,\n> +};\n> +\n> static struct attribute *clp_fw_attrs[] = {\n> \t&uid_checking_attr.attr,\n> \tNULL,\n> diff --git a/drivers/pci/slot.c b/drivers/pci/slot.c\n> index 787311614e5b6ebb39e7284f9b9f205a0a684d6d..2f8fcfbbec24e73d0bb6e40fd04c05a94f518045 100644\n> --- a/drivers/pci/slot.c\n> +++ b/drivers/pci/slot.c\n> @@ -96,7 +96,18 @@ static struct attribute *pci_slot_default_attrs[] = {\n> \t&pci_slot_attr_cur_speed.attr,\n> \tNULL,\n> };\n> -ATTRIBUTE_GROUPS(pci_slot_default);\n> +\n> +static const struct attribute_group pci_slot_default_group = {\n> +\t.attrs = pci_slot_default_attrs,\n> +};\n> +\n> +static const struct attribute_group *pci_slot_default_groups[] = {\n> +\t&pci_slot_default_group,\n> +#ifdef ARCH_PCI_SLOT_GROUPS\n> +\tARCH_PCI_SLOT_GROUPS,\n> +#endif\n> +\tNULL,\n> +};\n> \n> static const struct kobj_type pci_slot_ktype = {\n> \t.sysfs_ops = &pci_slot_sysfs_ops,\n>","headers":{"Return-Path":"\n ","X-Original-To":["incoming@patchwork.ozlabs.org","linux-pci@vger.kernel.org"],"Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=ibm.com header.i=@ibm.com header.a=rsa-sha256\n header.s=pp1 header.b=rZaItZL4;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=vger.kernel.org\n (client-ip=2600:3c04:e001:36c::12fc:5321; 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