PCI/IDE: Report available IDE streams

The limited number of link-encryption (IDE) streams that a given set of
host bridges supports is a platform specific detail. Provide
pci_ide_init_nr_streams() as a generic facility for either platform TSM
drivers, or PCI core native IDE, to report the number available streams.
After invoking pci_ide_init_nr_streams() an "available_secure_streams"
attribute appears in PCI host bridge sysfs to convey that count.

Introduce a device-type, @pci_host_bridge_type, now that both a release
method and sysfs attribute groups are being specified for all 'struct
pci_host_bridge' instances.

Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Lukas Wunner <lukas@wunner.de>
Cc: Samuel Ortiz <sameo@rivosinc.com>
Cc: Alexey Kardashevskiy <aik@amd.com>
Cc: Xu Yilun <yilun.xu@linux.intel.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Link: https://patch.msgid.link/20251031212902.2256310-9-dan.j.williams@intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Author: djbw

Documentation/ABI/testing/sysfs-devices-pci-host-bridge

@@ -31,3 +31,15 @@ Description:
 		platform specific pool of stream resources shared by the Root
 		Ports in a host bridge. See /sys/devices/pciDDDD:BB entry for
 		details about the DDDD:BB format.
+
+What:		pciDDDD:BB/available_secure_streams
+Contact:	linux-pci@vger.kernel.org
+Description:
+		(RO) When a host bridge has Root Ports that support PCIe IDE
+		(link encryption and integrity protection) there may be a
+		limited number of Selective IDE Streams that can be used for
+		establishing new end-to-end secure links. This attribute
+		decrements upon secure link setup, and increments upon secure
+		link teardown. The in-use stream count is determined by counting
+		stream symlinks. See /sys/devices/pciDDDD:BB entry for details
+		about the DDDD:BB format.

drivers/pci/ide.c

@@ -514,3 +514,70 @@ void pci_ide_init_host_bridge(struct pci_host_bridge *hb)
 	hb->nr_ide_streams = 256;
 	ida_init(&hb->ide_stream_ida);
 }
+
+static ssize_t available_secure_streams_show(struct device *dev,
+					     struct device_attribute *attr,
+					     char *buf)
+{
+	struct pci_host_bridge *hb = to_pci_host_bridge(dev);
+	int nr = READ_ONCE(hb->nr_ide_streams);
+	int avail = nr;
+
+	if (!nr)
+		return -ENXIO;
+
+	/*
+	 * Yes, this is inefficient and racy, but it is only for occasional
+	 * platform resource surveys. Worst case is bounded to 256 streams.
+	 */
+	for (int i = 0; i < nr; i++)
+		if (ida_exists(&hb->ide_stream_ida, i))
+			avail--;
+	return sysfs_emit(buf, "%d\n", avail);
+}
+static DEVICE_ATTR_RO(available_secure_streams);
+
+static struct attribute *pci_ide_attrs[] = {
+	&dev_attr_available_secure_streams.attr,
+	NULL
+};
+
+static umode_t pci_ide_attr_visible(struct kobject *kobj, struct attribute *a, int n)
+{
+	struct device *dev = kobj_to_dev(kobj);
+	struct pci_host_bridge *hb = to_pci_host_bridge(dev);
+
+	if (a == &dev_attr_available_secure_streams.attr)
+		if (!hb->nr_ide_streams)
+			return 0;
+
+	return a->mode;
+}
+
+const struct attribute_group pci_ide_attr_group = {
+	.attrs = pci_ide_attrs,
+	.is_visible = pci_ide_attr_visible,
+};
+
+/**
+ * pci_ide_set_nr_streams() - sets size of the pool of IDE Stream resources
+ * @hb: host bridge boundary for the stream pool
+ * @nr: number of streams
+ *
+ * Platform PCI init and/or expert test module use only. Limit IDE
+ * Stream establishment by setting the number of stream resources
+ * available at the host bridge. Platform init code must set this before
+ * the first pci_ide_stream_alloc() call if the platform has less than the
+ * default of 256 streams per host-bridge.
+ *
+ * The "PCI_IDE" symbol namespace is required because this is typically
+ * a detail that is settled in early PCI init. I.e. this export is not
+ * for endpoint drivers.
+ */
+void pci_ide_set_nr_streams(struct pci_host_bridge *hb, u16 nr)
+{
+	hb->nr_ide_streams = min(nr, 256);
+	WARN_ON_ONCE(!ida_is_empty(&hb->ide_stream_ida));
+	sysfs_update_group(&hb->dev.kobj, &pci_ide_attr_group);
+}
+EXPORT_SYMBOL_NS_GPL(pci_ide_set_nr_streams, "PCI_IDE");

drivers/pci/pci.h

@@ -616,6 +616,7 @@ static inline void pci_doe_sysfs_teardown(struct pci_dev *pdev) { }
 #ifdef CONFIG_PCI_IDE
 void pci_ide_init(struct pci_dev *dev);
 void pci_ide_init_host_bridge(struct pci_host_bridge *hb);
+extern const struct attribute_group pci_ide_attr_group;
 #else
 static inline void pci_ide_init(struct pci_dev *dev) { }
 static inline void pci_ide_init_host_bridge(struct pci_host_bridge *hb) { }

drivers/pci/probe.c

@@ -653,6 +653,18 @@ static void pci_release_host_bridge_dev(struct device *dev)
 	kfree(bridge);
 }
 
+static const struct attribute_group *pci_host_bridge_groups[] = {
+#ifdef CONFIG_PCI_IDE
+	&pci_ide_attr_group,
+#endif
+	NULL
+};
+
+static const struct device_type pci_host_bridge_type = {
+	.groups = pci_host_bridge_groups,
+	.release = pci_release_host_bridge_dev,
+};
+
 static void pci_init_host_bridge(struct pci_host_bridge *bridge)
 {
 	INIT_LIST_HEAD(&bridge->windows);
@@ -672,6 +684,7 @@ static void pci_init_host_bridge(struct pci_host_bridge *bridge)
 	bridge->native_dpc = 1;
 	bridge->domain_nr = PCI_DOMAIN_NR_NOT_SET;
 	bridge->native_cxl_error = 1;
+	bridge->dev.type = &pci_host_bridge_type;
 	pci_ide_init_host_bridge(bridge);
 
 	device_initialize(&bridge->dev);
@@ -686,7 +699,6 @@ struct pci_host_bridge *pci_alloc_host_bridge(size_t priv)
 		return NULL;
 
 	pci_init_host_bridge(bridge);
-	bridge->dev.release = pci_release_host_bridge_dev;
 
 	return bridge;
 }

include/linux/pci-ide.h

@@ -63,6 +63,7 @@ struct pci_ide {
 	const char *name;
 };
 
+void pci_ide_set_nr_streams(struct pci_host_bridge *hb, u16 nr);
 struct pci_ide_partner *pci_ide_to_settings(struct pci_dev *pdev,
 					    struct pci_ide *ide);
 struct pci_ide *pci_ide_stream_alloc(struct pci_dev *pdev);