[PATCH v3 04/13] PCI: Enable host-bridge emulation for PCI_DOMAINS_GENERIC platforms

[Dan Williams <dan.j.williams@intel.com>]

The ability to emulate a host-bridge is useful not only for hardware PCI
controllers like CONFIG_VMD, or virtual PCI controllers like
CONFIG_PCI_HYPERV, but also for test and development scenarios like
CONFIG_SAMPLES_DEVSEC [1].

One stumbling block for defining CONFIG_SAMPLES_DEVSEC, a sample
implementation of a platform TSM for PCI Device Security, is the need to
accommodate PCI_DOMAINS_GENERIC architectures alongside x86 [2].

In support of supplementing the existing CONFIG_PCI_BRIDGE_EMUL
infrastructure for host bridges:

* Introduce pci_bus_find_emul_domain_nr() as a common way to find a free
  PCI domain number whether that is to reuse the existing dynamic
  allocation code in the !ACPI case, or to assign an unused domain above
  the last ACPI segment.

* Convert pci-hyperv to the new allocator so that the PCI core can
  unconditionally assume that bridge->domain_nr != PCI_DOMAIN_NR_NOT_SET
  is the dynamically allocated case.

A follow on patch can also convert vmd to the new scheme. Currently vmd
is limited to CONFIG_PCI_DOMAINS_GENERIC=n (x86) so, unlike pci-hyperv,
it does not immediately conflict with this new
pci_bus_find_emul_domain_nr() mechanism.

Link: http://lore.kernel.org/174107249038.1288555.12362100502109498455.stgit@dwillia2-xfh.jf.intel.com [1]
Reported-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Closes: http://lore.kernel.org/20250311144601.145736-3-suzuki.poulose@arm.com
Cc: Lorenzo Pieralisi <lpieralisi@kernel.org>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Cc: Rob Herring <robh@kernel.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Wei Liu <wei.liu@kernel.org>
Cc: Dexuan Cui <decui@microsoft.com>
Tested-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 drivers/pci/controller/pci-hyperv.c | 53 ++---------------------------
 drivers/pci/pci.c                   | 43 ++++++++++++++++++++++-
 drivers/pci/probe.c                 |  8 ++++-
 include/linux/pci.h                 |  4 +++
 4 files changed, 56 insertions(+), 52 deletions(-)

diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
index ac27bda5ba26..8b624da2fdd7 100644
--- a/drivers/pci/controller/pci-hyperv.c
+++ b/drivers/pci/controller/pci-hyperv.c
@@ -3574,48 +3574,6 @@ static int hv_send_resources_released(struct hv_device *hdev)
 	return 0;
 }
 
-#define HVPCI_DOM_MAP_SIZE (64 * 1024)
-static DECLARE_BITMAP(hvpci_dom_map, HVPCI_DOM_MAP_SIZE);
-
-/*
- * PCI domain number 0 is used by emulated devices on Gen1 VMs, so define 0
- * as invalid for passthrough PCI devices of this driver.
- */
-#define HVPCI_DOM_INVALID 0
-
-/**
- * hv_get_dom_num() - Get a valid PCI domain number
- * Check if the PCI domain number is in use, and return another number if
- * it is in use.
- *
- * @dom: Requested domain number
- *
- * return: domain number on success, HVPCI_DOM_INVALID on failure
- */
-static u16 hv_get_dom_num(u16 dom)
-{
-	unsigned int i;
-
-	if (test_and_set_bit(dom, hvpci_dom_map) == 0)
-		return dom;
-
-	for_each_clear_bit(i, hvpci_dom_map, HVPCI_DOM_MAP_SIZE) {
-		if (test_and_set_bit(i, hvpci_dom_map) == 0)
-			return i;
-	}
-
-	return HVPCI_DOM_INVALID;
-}
-
-/**
- * hv_put_dom_num() - Mark the PCI domain number as free
- * @dom: Domain number to be freed
- */
-static void hv_put_dom_num(u16 dom)
-{
-	clear_bit(dom, hvpci_dom_map);
-}
-
 /**
  * hv_pci_probe() - New VMBus channel probe, for a root PCI bus
  * @hdev:	VMBus's tracking struct for this root PCI bus
@@ -3659,9 +3617,9 @@ static int hv_pci_probe(struct hv_device *hdev,
 	 * collisions) in the same VM.
 	 */
 	dom_req = hdev->dev_instance.b[5] << 8 | hdev->dev_instance.b[4];
-	dom = hv_get_dom_num(dom_req);
+	dom = pci_bus_find_emul_domain_nr(dom_req);
 
-	if (dom == HVPCI_DOM_INVALID) {
+	if (dom < 0) {
 		dev_err(&hdev->device,
 			"Unable to use dom# 0x%x or other numbers", dom_req);
 		ret = -EINVAL;
@@ -3795,7 +3753,7 @@ static int hv_pci_probe(struct hv_device *hdev,
 destroy_wq:
 	destroy_workqueue(hbus->wq);
 free_dom:
-	hv_put_dom_num(hbus->bridge->domain_nr);
+	pci_bus_release_emul_domain_nr(hbus->bridge->domain_nr);
 free_bus:
 	kfree(hbus);
 	return ret;
@@ -3919,8 +3877,6 @@ static void hv_pci_remove(struct hv_device *hdev)
 	irq_domain_remove(hbus->irq_domain);
 	irq_domain_free_fwnode(hbus->fwnode);
 
-	hv_put_dom_num(hbus->bridge->domain_nr);
-
 	kfree(hbus);
 }
 
@@ -4097,9 +4053,6 @@ static int __init init_hv_pci_drv(void)
 	if (ret)
 		return ret;
 
-	/* Set the invalid domain number's bit, so it will not be used */
-	set_bit(HVPCI_DOM_INVALID, hvpci_dom_map);
-
 	/* Initialize PCI block r/w interface */
 	hvpci_block_ops.read_block = hv_read_config_block;
 	hvpci_block_ops.write_block = hv_write_config_block;
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 4d7c9f64ea24..aea6bf37a360 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -6713,9 +6713,50 @@ static void pci_no_domains(void)
 #endif
 }
 
+#ifdef CONFIG_PCI_DOMAINS
+static DEFINE_IDA(pci_domain_nr_dynamic_ida);
+
+/*
+ * Find a free domain_nr either allocated by pci_domain_nr_dynamic_ida or
+ * fallback to the first free domain number above the last ACPI segment number.
+ * Caller may have a specific domain number in mind, in which case try to
+ * reserve it.
+ *
+ * Note that this allocation is freed by pci_release_host_bridge_dev().
+ */
+int pci_bus_find_emul_domain_nr(int hint)
+{
+	if (hint >= 0) {
+		hint = ida_alloc_range(&pci_domain_nr_dynamic_ida, hint, hint,
+				       GFP_KERNEL);
+
+		if (hint >= 0)
+			return hint;
+	}
+
+	if (acpi_disabled)
+		return ida_alloc(&pci_domain_nr_dynamic_ida, GFP_KERNEL);
+
+	/*
+	 * Emulated domains start at 0x10000 to not clash with ACPI _SEG
+	 * domains.  Per ACPI r6.0, sec 6.5.6,  _SEG returns an integer, of
+	 * which the lower 16 bits are the PCI Segment Group (domain) number.
+	 * Other bits are currently reserved.
+	 */
+	return ida_alloc_range(&pci_domain_nr_dynamic_ida, 0x10000, INT_MAX,
+			       GFP_KERNEL);
+}
+EXPORT_SYMBOL_GPL(pci_bus_find_emul_domain_nr);
+
+void pci_bus_release_emul_domain_nr(int domain_nr)
+{
+	ida_free(&pci_domain_nr_dynamic_ida, domain_nr);
+}
+EXPORT_SYMBOL_GPL(pci_bus_release_emul_domain_nr);
+#endif
+
 #ifdef CONFIG_PCI_DOMAINS_GENERIC
 static DEFINE_IDA(pci_domain_nr_static_ida);
-static DEFINE_IDA(pci_domain_nr_dynamic_ida);
 
 static void of_pci_reserve_static_domain_nr(void)
 {
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index c090289b70be..e4a7bb8b415f 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -632,6 +632,11 @@ static void pci_release_host_bridge_dev(struct device *dev)
 
 	pci_free_resource_list(&bridge->windows);
 	pci_free_resource_list(&bridge->dma_ranges);
+
+	/* Host bridges only have domain_nr set in the emulation case */
+	if (bridge->domain_nr != PCI_DOMAIN_NR_NOT_SET)
+		pci_bus_release_emul_domain_nr(bridge->domain_nr);
+
 	kfree(bridge);
 }
 
@@ -1112,7 +1117,8 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
 	device_del(&bridge->dev);
 free:
 #ifdef CONFIG_PCI_DOMAINS_GENERIC
-	pci_bus_release_domain_nr(parent, bus->domain_nr);
+	if (bridge->domain_nr == PCI_DOMAIN_NR_NOT_SET)
+		pci_bus_release_domain_nr(parent, bus->domain_nr);
 #endif
 	if (bus_registered)
 		put_device(&bus->dev);
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 72d07ad994fa..8962bf133316 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1894,10 +1894,14 @@ DEFINE_GUARD(pci_dev, struct pci_dev *, pci_dev_lock(_T), pci_dev_unlock(_T))
  */
 #ifdef CONFIG_PCI_DOMAINS
 extern int pci_domains_supported;
+int pci_bus_find_emul_domain_nr(int hint);
+void pci_bus_release_emul_domain_nr(int domain_nr);
 #else
 enum { pci_domains_supported = 0 };
 static inline int pci_domain_nr(struct pci_bus *bus) { return 0; }
 static inline int pci_proc_domain(struct pci_bus *bus) { return 0; }
+static inline int pci_bus_find_emul_domain_nr(int hint) { return 0; }
+static inline void pci_bus_release_emul_domain_nr(int domain_nr) { }
 #endif /* CONFIG_PCI_DOMAINS */
 
 /*
-- 
2.49.0