[RFC 1/1] s390/pci: expose UID checking state in sysfs

[Niklas Schnelle]

We use the UID of a zPCI adapter, or the UID of the function zero if
there are multiple functions in an adapter, as PCI domain if and only if
UID Checking is turned on.
Otherwise we automatically generate domains as devices appear.

The state of UID Checking is thus essential to know if the PCI domain
will be stable, yet currently there is no way to access this information
from userspace.
So let's solve this by showing the state of UID checking as a sysfs
attribute in /sys/bus/pci/uid_checking

Signed-off-by: Niklas Schnelle <schnelle@xxxxxxxxxxxxx>
---
 Documentation/ABI/testing/sysfs-bus-pci | 11 ++++++++
 arch/s390/include/asm/pci.h             |  3 +++
 arch/s390/pci/pci.c                     |  4 +++
 arch/s390/pci/pci_sysfs.c               | 34 +++++++++++++++++++++++++
 4 files changed, 52 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
index 25c9c39770c6..a174aac0ebb0 100644
--- a/Documentation/ABI/testing/sysfs-bus-pci
+++ b/Documentation/ABI/testing/sysfs-bus-pci
@@ -375,3 +375,14 @@ Description:
 		The value comes from the PCI kernel device state and can be one
 		of: "unknown", "error", "D0", D1", "D2", "D3hot", "D3cold".
 		The file is read only.
+What:		/sys/bus/pci/zpci/uid_checking
+Date:		December 2020
+Contact:	Niklas Schnelle <schnelle@xxxxxxxxxxxxx>
+Description:
+		This attribute exposes the global state of UID Checking on
+		an s390 Linux system. If UID Checking is on this file
+		contains '1' otherwise '0'. If UID Checking is on the UID of
+		a zPCI device, or the UID of function zero for a multi-function
+		device will be used as its PCI Domain number. If UID Checking
+		is off PCI Domain numbers are generated automatically and
+		are not stable across reboots.
diff --git a/arch/s390/include/asm/pci.h b/arch/s390/include/asm/pci.h
index 212628932ddc..3cfa6cc701ba 100644
--- a/arch/s390/include/asm/pci.h
+++ b/arch/s390/include/asm/pci.h
@@ -285,6 +285,9 @@ void zpci_debug_exit_device(struct zpci_dev *);
 /* Error reporting */
 int zpci_report_error(struct pci_dev *, struct zpci_report_error_header *);
 
+/* Sysfs Entries */
+int zpci_sysfs_init(void);
+
 #ifdef CONFIG_NUMA
 
 /* Returns the node based on PCI bus */
diff --git a/arch/s390/pci/pci.c b/arch/s390/pci/pci.c
index 41df8fcfddde..c16c93e5f9af 100644
--- a/arch/s390/pci/pci.c
+++ b/arch/s390/pci/pci.c
@@ -881,6 +881,10 @@ static int __init pci_base_init(void)
 	if (rc)
 		goto out_find;
 
+	rc = zpci_sysfs_init();
+	if (rc)
+		goto out_find;
+
 	s390_pci_initialized = 1;
 	return 0;
 
diff --git a/arch/s390/pci/pci_sysfs.c b/arch/s390/pci/pci_sysfs.c
index 5c028bee91b9..d00690f73539 100644
--- a/arch/s390/pci/pci_sysfs.c
+++ b/arch/s390/pci/pci_sysfs.c
@@ -172,3 +172,37 @@ const struct attribute_group *zpci_attr_groups[] = {
 	&pfip_attr_group,
 	NULL,
 };
+
+/* Global zPCI attributes */
+static ssize_t uid_checking_show(struct kobject *kobj,
+				 struct kobj_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%i\n", zpci_unique_uid);
+}
+
+static struct kobj_attribute sys_zpci_uid_checking_attr =
+	__ATTR(uid_checking, 0444, uid_checking_show, NULL);
+
+static struct kset *zpci_global_kset;
+
+static struct attribute *zpci_attrs_global[] = {
+	&sys_zpci_uid_checking_attr.attr,
+	NULL,
+};
+
+static struct attribute_group zpci_attr_group_global = {
+	.attrs = zpci_attrs_global,
+};
+
+int __init zpci_sysfs_init(void)
+{
+	struct kset *pci_bus_kset;
+
+	pci_bus_kset = bus_get_kset(&pci_bus_type);
+
+	zpci_global_kset = kset_create_and_add("zpci", NULL, &pci_bus_kset->kobj);
+	if (!zpci_global_kset)
+		return -ENOMEM;
+
+	return sysfs_create_group(&zpci_global_kset->kobj, &zpci_attr_group_global);
+}
-- 
2.17.1