Merge: [s390]: RHEL9 - s390/cio: add dev_busid sysfs entry for each subchannel

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9/-/merge_requests/1883
  
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2160493  

Tested: by IBM

Build-Info: https://brewweb.engineering.redhat.com/brew/taskinfo?taskID=50048757

Commits:
d3683c0 s390/cio: add dev_busid sysfs entry for each subchannel
a4751f1 s390/cio: check the subchannel validity for dev_busid

Signed-off-by: Tobias Huschle <thuschle@redhat.com>

Approved-by: Steve Best <sbest@redhat.com>
Approved-by: Tony Camuso <tcamuso@redhat.com>

Signed-off-by: Herton R. Krzesinski <herton@redhat.com>

Author: Herton R. Krzesinski

drivers/s390/cio/css.c

@@ -430,9 +430,26 @@ static ssize_t pimpampom_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(pimpampom);
 
+static ssize_t dev_busid_show(struct device *dev,
+			      struct device_attribute *attr,
+			      char *buf)
+{
+	struct subchannel *sch = to_subchannel(dev);
+	struct pmcw *pmcw = &sch->schib.pmcw;
+
+	if ((pmcw->st == SUBCHANNEL_TYPE_IO && pmcw->dnv) ||
+	    (pmcw->st == SUBCHANNEL_TYPE_MSG && pmcw->w))
+		return sysfs_emit(buf, "0.%x.%04x\n", sch->schid.ssid,
+				  pmcw->dev);
+	else
+		return sysfs_emit(buf, "none\n");
+}
+static DEVICE_ATTR_RO(dev_busid);
+
 static struct attribute *io_subchannel_type_attrs[] = {
 	&dev_attr_chpids.attr,
 	&dev_attr_pimpampom.attr,
+	&dev_attr_dev_busid.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(io_subchannel_type);