Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 788 insertions, 0 deletions

diff --git a/drivers/pci/of.c b/drivers/pci/of.c
new file mode 100644
index 0000000000..51e3dd0ea5
--- /dev/null
+++ b/drivers/pci/of.c
@@ -0,0 +1,788 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * PCI <-> OF mapping helpers
+ *
+ * Copyright 2011 IBM Corp.
+ */
+#define pr_fmt(fmt)	"PCI: OF: " fmt
+
+#include <linux/irqdomain.h>
+#include <linux/kernel.h>
+#include <linux/pci.h>
+#include <linux/of.h>
+#include <linux/of_irq.h>
+#include <linux/of_address.h>
+#include <linux/of_pci.h>
+#include "pci.h"
+
+#ifdef CONFIG_PCI
+/**
+ * pci_set_of_node - Find and set device's DT device_node
+ * @dev: the PCI device structure to fill
+ *
+ * Returns 0 on success with of_node set or when no device is described in the
+ * DT. Returns -ENODEV if the device is present, but disabled in the DT.
+ */
+int pci_set_of_node(struct pci_dev *dev)
+{
+	struct device_node *node;
+
+	if (!dev->bus->dev.of_node)
+		return 0;
+
+	node = of_pci_find_child_device(dev->bus->dev.of_node, dev->devfn);
+	if (!node)
+		return 0;
+
+	device_set_node(&dev->dev, of_fwnode_handle(node));
+	return 0;
+}
+
+void pci_release_of_node(struct pci_dev *dev)
+{
+	of_node_put(dev->dev.of_node);
+	device_set_node(&dev->dev, NULL);
+}
+
+void pci_set_bus_of_node(struct pci_bus *bus)
+{
+	struct device_node *node;
+
+	if (bus->self == NULL) {
+		node = pcibios_get_phb_of_node(bus);
+	} else {
+		node = of_node_get(bus->self->dev.of_node);
+		if (node && of_property_read_bool(node, "external-facing"))
+			bus->self->external_facing = true;
+	}
+
+	device_set_node(&bus->dev, of_fwnode_handle(node));
+}
+
+void pci_release_bus_of_node(struct pci_bus *bus)
+{
+	of_node_put(bus->dev.of_node);
+	device_set_node(&bus->dev, NULL);
+}
+
+struct device_node * __weak pcibios_get_phb_of_node(struct pci_bus *bus)
+{
+	/* This should only be called for PHBs */
+	if (WARN_ON(bus->self || bus->parent))
+		return NULL;
+
+	/*
+	 * Look for a node pointer in either the intermediary device we
+	 * create above the root bus or its own parent. Normally only
+	 * the later is populated.
+	 */
+	if (bus->bridge->of_node)
+		return of_node_get(bus->bridge->of_node);
+	if (bus->bridge->parent && bus->bridge->parent->of_node)
+		return of_node_get(bus->bridge->parent->of_node);
+	return NULL;
+}
+
+struct irq_domain *pci_host_bridge_of_msi_domain(struct pci_bus *bus)
+{
+#ifdef CONFIG_IRQ_DOMAIN
+	struct irq_domain *d;
+
+	if (!bus->dev.of_node)
+		return NULL;
+
+	/* Start looking for a phandle to an MSI controller. */
+	d = of_msi_get_domain(&bus->dev, bus->dev.of_node, DOMAIN_BUS_PCI_MSI);
+	if (d)
+		return d;
+
+	/*
+	 * If we don't have an msi-parent property, look for a domain
+	 * directly attached to the host bridge.
+	 */
+	d = irq_find_matching_host(bus->dev.of_node, DOMAIN_BUS_PCI_MSI);
+	if (d)
+		return d;
+
+	return irq_find_host(bus->dev.of_node);
+#else
+	return NULL;
+#endif
+}
+
+bool pci_host_of_has_msi_map(struct device *dev)
+{
+	if (dev && dev->of_node)
+		return of_get_property(dev->of_node, "msi-map", NULL);
+	return false;
+}
+
+static inline int __of_pci_pci_compare(struct device_node *node,
+				       unsigned int data)
+{
+	int devfn;
+
+	devfn = of_pci_get_devfn(node);
+	if (devfn < 0)
+		return 0;
+
+	return devfn == data;
+}
+
+struct device_node *of_pci_find_child_device(struct device_node *parent,
+					     unsigned int devfn)
+{
+	struct device_node *node, *node2;
+
+	for_each_child_of_node(parent, node) {
+		if (__of_pci_pci_compare(node, devfn))
+			return node;
+		/*
+		 * Some OFs create a parent node "multifunc-device" as
+		 * a fake root for all functions of a multi-function
+		 * device we go down them as well.
+		 */
+		if (of_node_name_eq(node, "multifunc-device")) {
+			for_each_child_of_node(node, node2) {
+				if (__of_pci_pci_compare(node2, devfn)) {
+					of_node_put(node);
+					return node2;
+				}
+			}
+		}
+	}
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(of_pci_find_child_device);
+
+/**
+ * of_pci_get_devfn() - Get device and function numbers for a device node
+ * @np: device node
+ *
+ * Parses a standard 5-cell PCI resource and returns an 8-bit value that can
+ * be passed to the PCI_SLOT() and PCI_FUNC() macros to extract the device
+ * and function numbers respectively. On error a negative error code is
+ * returned.
+ */
+int of_pci_get_devfn(struct device_node *np)
+{
+	u32 reg[5];
+	int error;
+
+	error = of_property_read_u32_array(np, "reg", reg, ARRAY_SIZE(reg));
+	if (error)
+		return error;
+
+	return (reg[0] >> 8) & 0xff;
+}
+EXPORT_SYMBOL_GPL(of_pci_get_devfn);
+
+/**
+ * of_pci_parse_bus_range() - parse the bus-range property of a PCI device
+ * @node: device node
+ * @res: address to a struct resource to return the bus-range
+ *
+ * Returns 0 on success or a negative error-code on failure.
+ */
+int of_pci_parse_bus_range(struct device_node *node, struct resource *res)
+{
+	u32 bus_range[2];
+	int error;
+
+	error = of_property_read_u32_array(node, "bus-range", bus_range,
+					   ARRAY_SIZE(bus_range));
+	if (error)
+		return error;
+
+	res->name = node->name;
+	res->start = bus_range[0];
+	res->end = bus_range[1];
+	res->flags = IORESOURCE_BUS;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(of_pci_parse_bus_range);
+
+/**
+ * of_get_pci_domain_nr - Find the host bridge domain number
+ *			  of the given device node.
+ * @node: Device tree node with the domain information.
+ *
+ * This function will try to obtain the host bridge domain number by finding
+ * a property called "linux,pci-domain" of the given device node.
+ *
+ * Return:
+ * * > 0	- On success, an associated domain number.
+ * * -EINVAL	- The property "linux,pci-domain" does not exist.
+ * * -ENODATA	- The linux,pci-domain" property does not have value.
+ * * -EOVERFLOW	- Invalid "linux,pci-domain" property value.
+ *
+ * Returns the associated domain number from DT in the range [0-0xffff], or
+ * a negative value if the required property is not found.
+ */
+int of_get_pci_domain_nr(struct device_node *node)
+{
+	u32 domain;
+	int error;
+
+	error = of_property_read_u32(node, "linux,pci-domain", &domain);
+	if (error)
+		return error;
+
+	return (u16)domain;
+}
+EXPORT_SYMBOL_GPL(of_get_pci_domain_nr);
+
+/**
+ * of_pci_check_probe_only - Setup probe only mode if linux,pci-probe-only
+ *                           is present and valid
+ */
+void of_pci_check_probe_only(void)
+{
+	u32 val;
+	int ret;
+
+	ret = of_property_read_u32(of_chosen, "linux,pci-probe-only", &val);
+	if (ret) {
+		if (ret == -ENODATA || ret == -EOVERFLOW)
+			pr_warn("linux,pci-probe-only without valid value, ignoring\n");
+		return;
+	}
+
+	if (val)
+		pci_add_flags(PCI_PROBE_ONLY);
+	else
+		pci_clear_flags(PCI_PROBE_ONLY);
+
+	pr_info("PROBE_ONLY %s\n", val ? "enabled" : "disabled");
+}
+EXPORT_SYMBOL_GPL(of_pci_check_probe_only);
+
+/**
+ * devm_of_pci_get_host_bridge_resources() - Resource-managed parsing of PCI
+ *                                           host bridge resources from DT
+ * @dev: host bridge device
+ * @busno: bus number associated with the bridge root bus
+ * @bus_max: maximum number of buses for this bridge
+ * @resources: list where the range of resources will be added after DT parsing
+ * @ib_resources: list where the range of inbound resources (with addresses
+ *                from 'dma-ranges') will be added after DT parsing
+ * @io_base: pointer to a variable that will contain on return the physical
+ * address for the start of the I/O range. Can be NULL if the caller doesn't
+ * expect I/O ranges to be present in the device tree.
+ *
+ * This function will parse the "ranges" property of a PCI host bridge device
+ * node and setup the resource mapping based on its content. It is expected
+ * that the property conforms with the Power ePAPR document.
+ *
+ * It returns zero if the range parsing has been successful or a standard error
+ * value if it failed.
+ */
+static int devm_of_pci_get_host_bridge_resources(struct device *dev,
+			unsigned char busno, unsigned char bus_max,
+			struct list_head *resources,
+			struct list_head *ib_resources,
+			resource_size_t *io_base)
+{
+	struct device_node *dev_node = dev->of_node;
+	struct resource *res, tmp_res;
+	struct resource *bus_range;
+	struct of_pci_range range;
+	struct of_pci_range_parser parser;
+	const char *range_type;
+	int err;
+
+	if (io_base)
+		*io_base = (resource_size_t)OF_BAD_ADDR;
+
+	bus_range = devm_kzalloc(dev, sizeof(*bus_range), GFP_KERNEL);
+	if (!bus_range)
+		return -ENOMEM;
+
+	dev_info(dev, "host bridge %pOF ranges:\n", dev_node);
+
+	err = of_pci_parse_bus_range(dev_node, bus_range);
+	if (err) {
+		bus_range->start = busno;
+		bus_range->end = bus_max;
+		bus_range->flags = IORESOURCE_BUS;
+		dev_info(dev, "  No bus range found for %pOF, using %pR\n",
+			 dev_node, bus_range);
+	} else {
+		if (bus_range->end > bus_range->start + bus_max)
+			bus_range->end = bus_range->start + bus_max;
+	}
+	pci_add_resource(resources, bus_range);
+
+	/* Check for ranges property */
+	err = of_pci_range_parser_init(&parser, dev_node);
+	if (err)
+		return 0;
+
+	dev_dbg(dev, "Parsing ranges property...\n");
+	for_each_of_pci_range(&parser, &range) {
+		/* Read next ranges element */
+		if ((range.flags & IORESOURCE_TYPE_BITS) == IORESOURCE_IO)
+			range_type = "IO";
+		else if ((range.flags & IORESOURCE_TYPE_BITS) == IORESOURCE_MEM)
+			range_type = "MEM";
+		else
+			range_type = "err";
+		dev_info(dev, "  %6s %#012llx..%#012llx -> %#012llx\n",
+			 range_type, range.cpu_addr,
+			 range.cpu_addr + range.size - 1, range.pci_addr);
+
+		/*
+		 * If we failed translation or got a zero-sized region
+		 * then skip this range
+		 */
+		if (range.cpu_addr == OF_BAD_ADDR || range.size == 0)
+			continue;
+
+		err = of_pci_range_to_resource(&range, dev_node, &tmp_res);
+		if (err)
+			continue;
+
+		res = devm_kmemdup(dev, &tmp_res, sizeof(tmp_res), GFP_KERNEL);
+		if (!res) {
+			err = -ENOMEM;
+			goto failed;
+		}
+
+		if (resource_type(res) == IORESOURCE_IO) {
+			if (!io_base) {
+				dev_err(dev, "I/O range found for %pOF. Please provide an io_base pointer to save CPU base address\n",
+					dev_node);
+				err = -EINVAL;
+				goto failed;
+			}
+			if (*io_base != (resource_size_t)OF_BAD_ADDR)
+				dev_warn(dev, "More than one I/O resource converted for %pOF. CPU base address for old range lost!\n",
+					 dev_node);
+			*io_base = range.cpu_addr;
+		} else if (resource_type(res) == IORESOURCE_MEM) {
+			res->flags &= ~IORESOURCE_MEM_64;
+		}
+
+		pci_add_resource_offset(resources, res,	res->start - range.pci_addr);
+	}
+
+	/* Check for dma-ranges property */
+	if (!ib_resources)
+		return 0;
+	err = of_pci_dma_range_parser_init(&parser, dev_node);
+	if (err)
+		return 0;
+
+	dev_dbg(dev, "Parsing dma-ranges property...\n");
+	for_each_of_pci_range(&parser, &range) {
+		/*
+		 * If we failed translation or got a zero-sized region
+		 * then skip this range
+		 */
+		if (((range.flags & IORESOURCE_TYPE_BITS) != IORESOURCE_MEM) ||
+		    range.cpu_addr == OF_BAD_ADDR || range.size == 0)
+			continue;
+
+		dev_info(dev, "  %6s %#012llx..%#012llx -> %#012llx\n",
+			 "IB MEM", range.cpu_addr,
+			 range.cpu_addr + range.size - 1, range.pci_addr);
+
+
+		err = of_pci_range_to_resource(&range, dev_node, &tmp_res);
+		if (err)
+			continue;
+
+		res = devm_kmemdup(dev, &tmp_res, sizeof(tmp_res), GFP_KERNEL);
+		if (!res) {
+			err = -ENOMEM;
+			goto failed;
+		}
+
+		pci_add_resource_offset(ib_resources, res,
+					res->start - range.pci_addr);
+	}
+
+	return 0;
+
+failed:
+	pci_free_resource_list(resources);
+	return err;
+}
+
+#if IS_ENABLED(CONFIG_OF_IRQ)
+/**
+ * of_irq_parse_pci - Resolve the interrupt for a PCI device
+ * @pdev:       the device whose interrupt is to be resolved
+ * @out_irq:    structure of_phandle_args filled by this function
+ *
+ * This function resolves the PCI interrupt for a given PCI device. If a
+ * device-node exists for a given pci_dev, it will use normal OF tree
+ * walking. If not, it will implement standard swizzling and walk up the
+ * PCI tree until an device-node is found, at which point it will finish
+ * resolving using the OF tree walking.
+ */
+static int of_irq_parse_pci(const struct pci_dev *pdev, struct of_phandle_args *out_irq)
+{
+	struct device_node *dn, *ppnode = NULL;
+	struct pci_dev *ppdev;
+	__be32 laddr[3];
+	u8 pin;
+	int rc;
+
+	/*
+	 * Check if we have a device node, if yes, fallback to standard
+	 * device tree parsing
+	 */
+	dn = pci_device_to_OF_node(pdev);
+	if (dn) {
+		rc = of_irq_parse_one(dn, 0, out_irq);
+		if (!rc)
+			return rc;
+	}
+
+	/*
+	 * Ok, we don't, time to have fun. Let's start by building up an
+	 * interrupt spec.  we assume #interrupt-cells is 1, which is standard
+	 * for PCI. If you do different, then don't use that routine.
+	 */
+	rc = pci_read_config_byte(pdev, PCI_INTERRUPT_PIN, &pin);
+	if (rc != 0)
+		goto err;
+	/* No pin, exit with no error message. */
+	if (pin == 0)
+		return -ENODEV;
+
+	/* Local interrupt-map in the device node? Use it! */
+	if (of_property_present(dn, "interrupt-map")) {
+		pin = pci_swizzle_interrupt_pin(pdev, pin);
+		ppnode = dn;
+	}
+
+	/* Now we walk up the PCI tree */
+	while (!ppnode) {
+		/* Get the pci_dev of our parent */
+		ppdev = pdev->bus->self;
+
+		/* Ouch, it's a host bridge... */
+		if (ppdev == NULL) {
+			ppnode = pci_bus_to_OF_node(pdev->bus);
+
+			/* No node for host bridge ? give up */
+			if (ppnode == NULL) {
+				rc = -EINVAL;
+				goto err;
+			}
+		} else {
+			/* We found a P2P bridge, check if it has a node */
+			ppnode = pci_device_to_OF_node(ppdev);
+		}
+
+		/*
+		 * Ok, we have found a parent with a device-node, hand over to
+		 * the OF parsing code.
+		 * We build a unit address from the linux device to be used for
+		 * resolution. Note that we use the linux bus number which may
+		 * not match your firmware bus numbering.
+		 * Fortunately, in most cases, interrupt-map-mask doesn't
+		 * include the bus number as part of the matching.
+		 * You should still be careful about that though if you intend
+		 * to rely on this function (you ship a firmware that doesn't
+		 * create device nodes for all PCI devices).
+		 */
+		if (ppnode)
+			break;
+
+		/*
+		 * We can only get here if we hit a P2P bridge with no node;
+		 * let's do standard swizzling and try again
+		 */
+		pin = pci_swizzle_interrupt_pin(pdev, pin);
+		pdev = ppdev;
+	}
+
+	out_irq->np = ppnode;
+	out_irq->args_count = 1;
+	out_irq->args[0] = pin;
+	laddr[0] = cpu_to_be32((pdev->bus->number << 16) | (pdev->devfn << 8));
+	laddr[1] = laddr[2] = cpu_to_be32(0);
+	rc = of_irq_parse_raw(laddr, out_irq);
+	if (rc)
+		goto err;
+	return 0;
+err:
+	if (rc == -ENOENT) {
+		dev_warn(&pdev->dev,
+			"%s: no interrupt-map found, INTx interrupts not available\n",
+			__func__);
+		pr_warn_once("%s: possibly some PCI slots don't have level triggered interrupts capability\n",
+			__func__);
+	} else {
+		dev_err(&pdev->dev, "%s: failed with rc=%d\n", __func__, rc);
+	}
+	return rc;
+}
+
+/**
+ * of_irq_parse_and_map_pci() - Decode a PCI IRQ from the device tree and map to a VIRQ
+ * @dev: The PCI device needing an IRQ
+ * @slot: PCI slot number; passed when used as map_irq callback. Unused
+ * @pin: PCI IRQ pin number; passed when used as map_irq callback. Unused
+ *
+ * @slot and @pin are unused, but included in the function so that this
+ * function can be used directly as the map_irq callback to
+ * pci_assign_irq() and struct pci_host_bridge.map_irq pointer
+ */
+int of_irq_parse_and_map_pci(const struct pci_dev *dev, u8 slot, u8 pin)
+{
+	struct of_phandle_args oirq;
+	int ret;
+
+	ret = of_irq_parse_pci(dev, &oirq);
+	if (ret)
+		return 0; /* Proper return code 0 == NO_IRQ */
+
+	return irq_create_of_mapping(&oirq);
+}
+EXPORT_SYMBOL_GPL(of_irq_parse_and_map_pci);
+#endif	/* CONFIG_OF_IRQ */
+
+static int pci_parse_request_of_pci_ranges(struct device *dev,
+					   struct pci_host_bridge *bridge)
+{
+	int err, res_valid = 0;
+	resource_size_t iobase;
+	struct resource_entry *win, *tmp;
+
+	INIT_LIST_HEAD(&bridge->windows);
+	INIT_LIST_HEAD(&bridge->dma_ranges);
+
+	err = devm_of_pci_get_host_bridge_resources(dev, 0, 0xff, &bridge->windows,
+						    &bridge->dma_ranges, &iobase);
+	if (err)
+		return err;
+
+	err = devm_request_pci_bus_resources(dev, &bridge->windows);
+	if (err)
+		return err;
+
+	resource_list_for_each_entry_safe(win, tmp, &bridge->windows) {
+		struct resource *res = win->res;
+
+		switch (resource_type(res)) {
+		case IORESOURCE_IO:
+			err = devm_pci_remap_iospace(dev, res, iobase);
+			if (err) {
+				dev_warn(dev, "error %d: failed to map resource %pR\n",
+					 err, res);
+				resource_list_destroy_entry(win);
+			}
+			break;
+		case IORESOURCE_MEM:
+			res_valid |= !(res->flags & IORESOURCE_PREFETCH);
+
+			if (!(res->flags & IORESOURCE_PREFETCH))
+				if (upper_32_bits(resource_size(res)))
+					dev_warn(dev, "Memory resource size exceeds max for 32 bits\n");
+
+			break;
+		}
+	}
+
+	if (!res_valid)
+		dev_warn(dev, "non-prefetchable memory resource required\n");
+
+	return 0;
+}
+
+int devm_of_pci_bridge_init(struct device *dev, struct pci_host_bridge *bridge)
+{
+	if (!dev->of_node)
+		return 0;
+
+	bridge->swizzle_irq = pci_common_swizzle;
+	bridge->map_irq = of_irq_parse_and_map_pci;
+
+	return pci_parse_request_of_pci_ranges(dev, bridge);
+}
+
+#ifdef CONFIG_PCI_DYNAMIC_OF_NODES
+
+void of_pci_remove_node(struct pci_dev *pdev)
+{
+	struct device_node *np;
+
+	np = pci_device_to_OF_node(pdev);
+	if (!np || !of_node_check_flag(np, OF_DYNAMIC))
+		return;
+	pdev->dev.of_node = NULL;
+
+	of_changeset_revert(np->data);
+	of_changeset_destroy(np->data);
+	of_node_put(np);
+}
+
+void of_pci_make_dev_node(struct pci_dev *pdev)
+{
+	struct device_node *ppnode, *np = NULL;
+	const char *pci_type;
+	struct of_changeset *cset;
+	const char *name;
+	int ret;
+
+	/*
+	 * If there is already a device tree node linked to this device,
+	 * return immediately.
+	 */
+	if (pci_device_to_OF_node(pdev))
+		return;
+
+	/* Check if there is device tree node for parent device */
+	if (!pdev->bus->self)
+		ppnode = pdev->bus->dev.of_node;
+	else
+		ppnode = pdev->bus->self->dev.of_node;
+	if (!ppnode)
+		return;
+
+	if (pci_is_bridge(pdev))
+		pci_type = "pci";
+	else
+		pci_type = "dev";
+
+	name = kasprintf(GFP_KERNEL, "%s@%x,%x", pci_type,
+			 PCI_SLOT(pdev->devfn), PCI_FUNC(pdev->devfn));
+	if (!name)
+		return;
+
+	cset = kmalloc(sizeof(*cset), GFP_KERNEL);
+	if (!cset)
+		goto out_free_name;
+	of_changeset_init(cset);
+
+	np = of_changeset_create_node(cset, ppnode, name);
+	if (!np)
+		goto out_destroy_cset;
+
+	ret = of_pci_add_properties(pdev, cset, np);
+	if (ret)
+		goto out_free_node;
+
+	ret = of_changeset_apply(cset);
+	if (ret)
+		goto out_free_node;
+
+	np->data = cset;
+	pdev->dev.of_node = np;
+	kfree(name);
+
+	return;
+
+out_free_node:
+	of_node_put(np);
+out_destroy_cset:
+	of_changeset_destroy(cset);
+	kfree(cset);
+out_free_name:
+	kfree(name);
+}
+#endif
+
+#endif /* CONFIG_PCI */
+
+/**
+ * of_pci_get_max_link_speed - Find the maximum link speed of the given device node.
+ * @node: Device tree node with the maximum link speed information.
+ *
+ * This function will try to find the limitation of link speed by finding
+ * a property called "max-link-speed" of the given device node.
+ *
+ * Return:
+ * * > 0	- On success, a maximum link speed.
+ * * -EINVAL	- Invalid "max-link-speed" property value, or failure to access
+ *		  the property of the device tree node.
+ *
+ * Returns the associated max link speed from DT, or a negative value if the
+ * required property is not found or is invalid.
+ */
+int of_pci_get_max_link_speed(struct device_node *node)
+{
+	u32 max_link_speed;
+
+	if (of_property_read_u32(node, "max-link-speed", &max_link_speed) ||
+	    max_link_speed == 0 || max_link_speed > 4)
+		return -EINVAL;
+
+	return max_link_speed;
+}
+EXPORT_SYMBOL_GPL(of_pci_get_max_link_speed);
+
+/**
+ * of_pci_get_slot_power_limit - Parses the "slot-power-limit-milliwatt"
+ *				 property.
+ *
+ * @node: device tree node with the slot power limit information
+ * @slot_power_limit_value: pointer where the value should be stored in PCIe
+ *			    Slot Capabilities Register format
+ * @slot_power_limit_scale: pointer where the scale should be stored in PCIe
+ *			    Slot Capabilities Register format
+ *
+ * Returns the slot power limit in milliwatts and if @slot_power_limit_value
+ * and @slot_power_limit_scale pointers are non-NULL, fills in the value and
+ * scale in format used by PCIe Slot Capabilities Register.
+ *
+ * If the property is not found or is invalid, returns 0.
+ */
+u32 of_pci_get_slot_power_limit(struct device_node *node,
+				u8 *slot_power_limit_value,
+				u8 *slot_power_limit_scale)
+{
+	u32 slot_power_limit_mw;
+	u8 value, scale;
+
+	if (of_property_read_u32(node, "slot-power-limit-milliwatt",
+				 &slot_power_limit_mw))
+		slot_power_limit_mw = 0;
+
+	/* Calculate Slot Power Limit Value and Slot Power Limit Scale */
+	if (slot_power_limit_mw == 0) {
+		value = 0x00;
+		scale = 0;
+	} else if (slot_power_limit_mw <= 255) {
+		value = slot_power_limit_mw;
+		scale = 3;
+	} else if (slot_power_limit_mw <= 255*10) {
+		value = slot_power_limit_mw / 10;
+		scale = 2;
+		slot_power_limit_mw = slot_power_limit_mw / 10 * 10;
+	} else if (slot_power_limit_mw <= 255*100) {
+		value = slot_power_limit_mw / 100;
+		scale = 1;
+		slot_power_limit_mw = slot_power_limit_mw / 100 * 100;
+	} else if (slot_power_limit_mw <= 239*1000) {
+		value = slot_power_limit_mw / 1000;
+		scale = 0;
+		slot_power_limit_mw = slot_power_limit_mw / 1000 * 1000;
+	} else if (slot_power_limit_mw < 250*1000) {
+		value = 0xEF;
+		scale = 0;
+		slot_power_limit_mw = 239*1000;
+	} else if (slot_power_limit_mw <= 600*1000) {
+		value = 0xF0 + (slot_power_limit_mw / 1000 - 250) / 25;
+		scale = 0;
+		slot_power_limit_mw = slot_power_limit_mw / (1000*25) * (1000*25);
+	} else {
+		value = 0xFE;
+		scale = 0;
+		slot_power_limit_mw = 600*1000;
+	}
+
+	if (slot_power_limit_value)
+		*slot_power_limit_value = value;
+
+	if (slot_power_limit_scale)
+		*slot_power_limit_scale = scale;
+
+	return slot_power_limit_mw;
+}
+EXPORT_SYMBOL_GPL(of_pci_get_slot_power_limit);