PCI: Add pci_resize_resource() for resizing BARs

Add a pci_resize_resource() interface to allow device drivers to resize
BARs of their devices.

This is useful for devices with large local storage, e.g., graphics
devices.  These devices often only expose 256MB BARs initially to be
compatible with 32-bit systems.

This function only tries to reprogram the windows of the bridge directly
above the requesting device and only the BAR of the same type (usually mem,
64bit, prefetchable).  This is done to avoid disturbing other drivers by
changing the BARs of their devices.

Drivers should use the following sequence to resize their BARs:
1. Disable memory decoding of the device using the PCI cfg dword.
2. Use pci_release_resource() to release all BARs which can move during the
   resize, including the one you want to resize.
3. Call pci_resize_resource() for each BAR you want to resize.
4. Call pci_assign_unassigned_bus_resources() to reassign new locations
   for all BARs which are not resized, but could move.
5. If everything worked as expected, enable memory decoding in the device
   again using the PCI cfg dword.

Signed-off-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

3 files changed, 159 insertions, 0 deletions

diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index 73dda0d59bbc..6826a893288a 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -1913,6 +1913,104 @@ enable_all:
 }
 EXPORT_SYMBOL_GPL(pci_assign_unassigned_bridge_resources);
 
+int pci_reassign_bridge_resources(struct pci_dev *bridge, unsigned long type)
+{
+	struct pci_dev_resource *dev_res;
+	struct pci_dev *next;
+	LIST_HEAD(saved);
+	LIST_HEAD(added);
+	LIST_HEAD(failed);
+	unsigned int i;
+	int ret;
+
+	/* Walk to the root hub, releasing bridge BARs when possible */
+	next = bridge;
+	do {
+		bridge = next;
+		for (i = PCI_BRIDGE_RESOURCES; i < PCI_BRIDGE_RESOURCE_END;
+		     i++) {
+			struct resource *res = &bridge->resource[i];
+
+			if ((res->flags ^ type) & PCI_RES_TYPE_MASK)
+				continue;
+
+			/* Ignore BARs which are still in use */
+			if (res->child)
+				continue;
+
+			ret = add_to_list(&saved, bridge, res, 0, 0);
+			if (ret)
+				goto cleanup;
+
+			dev_info(&bridge->dev, "BAR %d: releasing %pR\n",
+				 i, res);
+
+			if (res->parent)
+				release_resource(res);
+			res->start = 0;
+			res->end = 0;
+			break;
+		}
+		if (i == PCI_BRIDGE_RESOURCE_END)
+			break;
+
+		next = bridge->bus ? bridge->bus->self : NULL;
+	} while (next);
+
+	if (list_empty(&saved))
+		return -ENOENT;
+
+	__pci_bus_size_bridges(bridge->subordinate, &added);
+	__pci_bridge_assign_resources(bridge, &added, &failed);
+	BUG_ON(!list_empty(&added));
+
+	if (!list_empty(&failed)) {
+		ret = -ENOSPC;
+		goto cleanup;
+	}
+
+	list_for_each_entry(dev_res, &saved, list) {
+		/* Skip the bridge we just assigned resources for. */
+		if (bridge == dev_res->dev)
+			continue;
+
+		bridge = dev_res->dev;
+		pci_setup_bridge(bridge->subordinate);
+	}
+
+	free_list(&saved);
+	return 0;
+
+cleanup:
+	/* restore size and flags */
+	list_for_each_entry(dev_res, &failed, list) {
+		struct resource *res = dev_res->res;
+
+		res->start = dev_res->start;
+		res->end = dev_res->end;
+		res->flags = dev_res->flags;
+	}
+	free_list(&failed);
+
+	/* Revert to the old configuration */
+	list_for_each_entry(dev_res, &saved, list) {
+		struct resource *res = dev_res->res;
+
+		bridge = dev_res->dev;
+		i = res - bridge->resource;
+
+		res->start = dev_res->start;
+		res->end = dev_res->end;
+		res->flags = dev_res->flags;
+
+		pci_claim_resource(bridge, i);
+		pci_setup_bridge(bridge->subordinate);
+	}
+	free_list(&saved);
+
+	return ret;
+}
+
 void pci_assign_unassigned_bus_resources(struct pci_bus *bus)
 {
 	struct pci_dev *dev;
diff --git a/drivers/pci/setup-res.c b/drivers/pci/setup-res.c
index e576e1a8d978..bf0089ef2177 100644
--- a/drivers/pci/setup-res.c
+++ b/drivers/pci/setup-res.c
@@ -396,6 +396,64 @@ int pci_reassign_resource(struct pci_dev *dev, int resno, resource_size_t addsiz
 	return 0;
 }
 
+void pci_release_resource(struct pci_dev *dev, int resno)
+{
+	struct resource *res = dev->resource + resno;
+
+	dev_info(&dev->dev, "BAR %d: releasing %pR\n", resno, res);
+	release_resource(res);
+	res->end = resource_size(res) - 1;
+	res->start = 0;
+	res->flags |= IORESOURCE_UNSET;
+}
+EXPORT_SYMBOL(pci_release_resource);
+
+int pci_resize_resource(struct pci_dev *dev, int resno, int size)
+{
+	struct resource *res = dev->resource + resno;
+	int old, ret;
+	u32 sizes;
+	u16 cmd;
+
+	/* Make sure the resource isn't assigned before resizing it. */
+	if (!(res->flags & IORESOURCE_UNSET))
+		return -EBUSY;
+
+	pci_read_config_word(dev, PCI_COMMAND, &cmd);
+	if (cmd & PCI_COMMAND_MEMORY)
+		return -EBUSY;
+
+	sizes = pci_rebar_get_possible_sizes(dev, resno);
+	if (!sizes)
+		return -ENOTSUPP;
+
+	if (!(sizes & BIT(size)))
+		return -EINVAL;
+
+	old = pci_rebar_get_current_size(dev, resno);
+	if (old < 0)
+		return old;
+
+	ret = pci_rebar_set_size(dev, resno, size);
+	if (ret)
+		return ret;
+
+	res->end = res->start + pci_rebar_size_to_bytes(size) - 1;
+
+	/* Check if the new config works by trying to assign everything. */
+	ret = pci_reassign_bridge_resources(dev->bus->self, res->flags);
+	if (ret)
+		goto error_resize;
+
+	return 0;
+
+error_resize:
+	pci_rebar_set_size(dev, resno, old);
+	res->end = res->start + pci_rebar_size_to_bytes(old) - 1;
+	return ret;
+}
+EXPORT_SYMBOL(pci_resize_resource);
+
 int pci_enable_resources(struct pci_dev *dev, int mask)
 {
 	u16 cmd, old_cmd;
diff --git a/include/linux/pci.h b/include/linux/pci.h
index f4f8ee5a7362..55e9fe6dd577 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1106,6 +1106,8 @@ void pci_reset_bridge_secondary_bus(struct pci_dev *dev);
 void pci_update_resource(struct pci_dev *dev, int resno);
 int __must_check pci_assign_resource(struct pci_dev *dev, int i);
 int __must_check pci_reassign_resource(struct pci_dev *dev, int i, resource_size_t add_size, resource_size_t align);
+void pci_release_resource(struct pci_dev *dev, int resno);
+int __must_check pci_resize_resource(struct pci_dev *dev, int i, int size);
 int pci_select_bars(struct pci_dev *dev, unsigned long flags);
 bool pci_device_is_present(struct pci_dev *pdev);
 void pci_ignore_hotplug(struct pci_dev *dev);
@@ -1185,6 +1187,7 @@ void pci_assign_unassigned_resources(void);
 void pci_assign_unassigned_bridge_resources(struct pci_dev *bridge);
 void pci_assign_unassigned_bus_resources(struct pci_bus *bus);
 void pci_assign_unassigned_root_bus_resources(struct pci_bus *bus);
+int pci_reassign_bridge_resources(struct pci_dev *bridge, unsigned long type);
 void pdev_enable_device(struct pci_dev *);
 int pci_enable_resources(struct pci_dev *, int mask);
 void pci_assign_irq(struct pci_dev *dev);