1 files changed, 263 insertions, 0 deletions
diff --git a/drivers/platform/x86/p2sb.c b/drivers/platform/x86/p2sb.c
new file mode 100644
index 000000000000..cbbb0f809704
--- /dev/null
+++ b/drivers/platform/x86/p2sb.c
@@ -0,0 +1,263 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Primary to Sideband (P2SB) bridge access support
+ *
+ * Copyright (c) 2017, 2021-2022 Intel Corporation.
+ *
+ * Authors: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
+ *	    Jonathan Yong <jonathan.yong@intel.com>
+ */
+
+#include <linux/bits.h>
+#include <linux/export.h>
+#include <linux/pci.h>
+#include <linux/platform_data/x86/p2sb.h>
+
+#include <asm/cpu_device_id.h>
+#include <asm/intel-family.h>
+
+#define P2SBC			0xe0
+#define P2SBC_HIDE		BIT(8)
+
+#define P2SB_DEVFN_DEFAULT	PCI_DEVFN(31, 1)
+#define P2SB_DEVFN_GOLDMONT	PCI_DEVFN(13, 0)
+#define SPI_DEVFN_GOLDMONT	PCI_DEVFN(13, 2)
+
+static const struct x86_cpu_id p2sb_cpu_ids[] = {
+	X86_MATCH_VFM(INTEL_ATOM_GOLDMONT, P2SB_DEVFN_GOLDMONT),
+	X86_MATCH_VFM(INTEL_ATOM_GOLDMONT_PLUS, P2SB_DEVFN_GOLDMONT),
+	{}
+};
+
+/*
+ * Cache BAR0 of P2SB device functions 0 to 7.
+ * TODO: The constant 8 is the number of functions that PCI specification
+ *       defines. Same definitions exist tree-wide. Unify this definition and
+ *       the other definitions then move to include/uapi/linux/pci.h.
+ */
+#define NR_P2SB_RES_CACHE 8
+
+struct p2sb_res_cache {
+	u32 bus_dev_id;
+	struct resource res;
+};
+
+static struct p2sb_res_cache p2sb_resources[NR_P2SB_RES_CACHE];
+static bool p2sb_hidden_by_bios;
+
+static void p2sb_get_devfn(unsigned int *devfn)
+{
+	unsigned int fn = P2SB_DEVFN_DEFAULT;
+	const struct x86_cpu_id *id;
+
+	id = x86_match_cpu(p2sb_cpu_ids);
+	if (id)
+		fn = (unsigned int)id->driver_data;
+
+	*devfn = fn;
+}
+
+static bool p2sb_valid_resource(const struct resource *res)
+{
+	return res->flags & ~IORESOURCE_UNSET;
+}
+
+/* Copy resource from the first BAR of the device in question */
+static void p2sb_read_bar0(struct pci_dev *pdev, struct resource *mem)
+{
+	struct resource *bar0 = pci_resource_n(pdev, 0);
+
+	/* Make sure we have no dangling pointers in the output */
+	memset(mem, 0, sizeof(*mem));
+
+	/*
+	 * We copy only selected fields from the original resource.
+	 * Because a PCI device will be removed soon, we may not use
+	 * any allocated data, hence we may not copy any pointers.
+	 */
+	mem->start = bar0->start;
+	mem->end = bar0->end;
+	mem->flags = bar0->flags;
+	mem->desc = bar0->desc;
+}
+
+static void p2sb_scan_and_cache_devfn(struct pci_bus *bus, unsigned int devfn)
+{
+	struct p2sb_res_cache *cache = &p2sb_resources[PCI_FUNC(devfn)];
+	struct pci_dev *pdev;
+
+	pdev = pci_scan_single_device(bus, devfn);
+	if (!pdev)
+		return;
+
+	p2sb_read_bar0(pdev, &cache->res);
+	cache->bus_dev_id = bus->dev.id;
+
+	pci_stop_and_remove_bus_device(pdev);
+}
+
+static int p2sb_scan_and_cache(struct pci_bus *bus, unsigned int devfn)
+{
+	/*
+	 * The BIOS prevents the P2SB device from being enumerated by the PCI
+	 * subsystem, so we need to unhide and hide it back to lookup the BAR.
+	 */
+	pci_bus_write_config_dword(bus, devfn, P2SBC, 0);
+
+	/* Scan the P2SB device and cache its BAR0 */
+	p2sb_scan_and_cache_devfn(bus, devfn);
+
+	/* On Goldmont p2sb_bar() also gets called for the SPI controller */
+	if (devfn == P2SB_DEVFN_GOLDMONT)
+		p2sb_scan_and_cache_devfn(bus, SPI_DEVFN_GOLDMONT);
+
+	pci_bus_write_config_dword(bus, devfn, P2SBC, P2SBC_HIDE);
+
+	if (!p2sb_valid_resource(&p2sb_resources[PCI_FUNC(devfn)].res))
+		return -ENOENT;
+
+	return 0;
+}
+
+static struct pci_bus *p2sb_get_bus(struct pci_bus *bus)
+{
+	static struct pci_bus *p2sb_bus;
+
+	bus = bus ?: p2sb_bus;
+	if (bus)
+		return bus;
+
+	/* Assume P2SB is on the bus 0 in domain 0 */
+	p2sb_bus = pci_find_bus(0, 0);
+	return p2sb_bus;
+}
+
+static int p2sb_cache_resources(void)
+{
+	unsigned int devfn_p2sb;
+	u32 value = P2SBC_HIDE;
+	struct pci_bus *bus;
+	u16 class;
+	int ret = 0;
+
+	/* Get devfn for P2SB device itself */
+	p2sb_get_devfn(&devfn_p2sb);
+
+	bus = p2sb_get_bus(NULL);
+	if (!bus)
+		return -ENODEV;
+
+	/*
+	 * When a device with same devfn exists and its device class is not
+	 * PCI_CLASS_MEMORY_OTHER for P2SB, do not touch it.
+	 */
+	pci_bus_read_config_word(bus, devfn_p2sb, PCI_CLASS_DEVICE, &class);
+	if (!PCI_POSSIBLE_ERROR(class) && class != PCI_CLASS_MEMORY_OTHER)
+		return -ENODEV;
+
+	/*
+	 * Prevent concurrent PCI bus scan from seeing the P2SB device and
+	 * removing via sysfs while it is temporarily exposed.
+	 */
+	pci_lock_rescan_remove();
+
+	pci_bus_read_config_dword(bus, devfn_p2sb, P2SBC, &value);
+	p2sb_hidden_by_bios = value & P2SBC_HIDE;
+
+	/*
+	 * If the BIOS does not hide the P2SB device then its resources
+	 * are accesilble. Cache them only if the P2SB device is hidden.
+	 */
+	if (p2sb_hidden_by_bios)
+		ret = p2sb_scan_and_cache(bus, devfn_p2sb);
+
+	pci_unlock_rescan_remove();
+
+	return ret;
+}
+
+static int p2sb_read_from_cache(struct pci_bus *bus, unsigned int devfn,
+				struct resource *mem)
+{
+	struct p2sb_res_cache *cache = &p2sb_resources[PCI_FUNC(devfn)];
+
+	if (cache->bus_dev_id != bus->dev.id)
+		return -ENODEV;
+
+	if (!p2sb_valid_resource(&cache->res))
+		return -ENOENT;
+
+	memcpy(mem, &cache->res, sizeof(*mem));
+
+	return 0;
+}
+
+static int p2sb_read_from_dev(struct pci_bus *bus, unsigned int devfn,
+			      struct resource *mem)
+{
+	struct pci_dev *pdev;
+	int ret = 0;
+
+	pdev = pci_get_slot(bus, devfn);
+	if (!pdev)
+		return -ENODEV;
+
+	if (p2sb_valid_resource(pci_resource_n(pdev, 0)))
+		p2sb_read_bar0(pdev, mem);
+	else
+		ret = -ENOENT;
+
+	pci_dev_put(pdev);
+
+	return ret;
+}
+
+/**
+ * p2sb_bar - Get Primary to Sideband (P2SB) bridge device BAR
+ * @bus: PCI bus to communicate with
+ * @devfn: PCI slot and function to communicate with
+ * @mem: memory resource to be filled in
+ *
+ * If @bus is NULL, the bus 0 in domain 0 will be used.
+ * If @devfn is 0, it will be replaced by devfn of the P2SB device.
+ *
+ * Caller must provide a valid pointer to @mem.
+ *
+ * Return:
+ * 0 on success or appropriate errno value on error.
+ */
+int p2sb_bar(struct pci_bus *bus, unsigned int devfn, struct resource *mem)
+{
+	bus = p2sb_get_bus(bus);
+	if (!bus)
+		return -ENODEV;
+
+	if (!devfn)
+		p2sb_get_devfn(&devfn);
+
+	if (p2sb_hidden_by_bios)
+		return p2sb_read_from_cache(bus, devfn, mem);
+
+	return p2sb_read_from_dev(bus, devfn, mem);
+}
+EXPORT_SYMBOL_GPL(p2sb_bar);
+
+static int __init p2sb_fs_init(void)
+{
+	return p2sb_cache_resources();
+}
+
+/*
+ * pci_rescan_remove_lock() can not be locked in sysfs PCI bus rescan path
+ * because of deadlock. To avoid the deadlock, access P2SB devices with the lock
+ * at an early step in kernel initialization and cache required resources.
+ *
+ * We want to run as early as possible. If the P2SB was assigned a bad BAR,
+ * we'll need to wait on pcibios_assign_resources() to fix it. So, our list of
+ * initcall dependencies looks something like this:
+ *
+ * ...
+ * subsys_initcall (pci_subsys_init)
+ * fs_initcall     (pcibios_assign_resources)
+ */
+fs_initcall_sync(p2sb_fs_init);