[v5,1/8] platform/x86/intel: Add Primary to Sideband (P2SB) bridge support

diff --git a/drivers/platform/x86/intel/Kconfig b/drivers/platform/x86/intel/Kconfig
index 1f01a8a23c57..f0c4334bc0ca 100644
--- a/drivers/platform/x86/intel/Kconfig
+++ b/drivers/platform/x86/intel/Kconfig
@@ -69,6 +69,18 @@  config INTEL_OAKTRAIL
 	  enable/disable the Camera, WiFi, BT etc. devices. If in doubt, say Y
 	  here; it will only load on supported platforms.
 
+config P2SB
+	bool "Primary to Sideband (P2SB) bridge access support"
+	depends on PCI
+	help
+	  The Primary to Sideband (P2SB) bridge is an interface to some
+	  PCI devices connected through it. In particular, SPI NOR controller
+	  in Intel Apollo Lake SoC is one of such devices.
+
+	  The main purpose of this library is to unhide P2SB device in case
+	  firmware kept it hidden on some platforms in order to access devices
+	  behind it.
+
 config INTEL_BXTWC_PMIC_TMU
 	tristate "Intel Broxton Whiskey Cove TMU Driver"
 	depends on INTEL_SOC_PMIC_BXTWC
diff --git a/drivers/platform/x86/intel/Makefile b/drivers/platform/x86/intel/Makefile
index c61bc3e97121..8a999f70e55c 100644
--- a/drivers/platform/x86/intel/Makefile
+++ b/drivers/platform/x86/intel/Makefile
@@ -27,6 +27,8 @@  intel_int0002_vgpio-y			:= int0002_vgpio.o
 obj-$(CONFIG_INTEL_INT0002_VGPIO)	+= intel_int0002_vgpio.o
 intel_oaktrail-y			:= oaktrail.o
 obj-$(CONFIG_INTEL_OAKTRAIL)		+= intel_oaktrail.o
+intel_p2sb-y				:= p2sb.o
+obj-$(CONFIG_P2SB)			+= intel_p2sb.o
 intel_sdsi-y				:= sdsi.o
 obj-$(CONFIG_INTEL_SDSI)		+= intel_sdsi.o
 intel_vsec-y				:= vsec.o
diff --git a/drivers/platform/x86/intel/p2sb.c b/drivers/platform/x86/intel/p2sb.c
new file mode 100644
index 000000000000..b598ef14dbc6
--- /dev/null
+++ b/drivers/platform/x86/intel/p2sb.c
@@ -0,0 +1,127 @@ 
+// 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)
+
+static const struct x86_cpu_id p2sb_cpu_ids[] = {
+	X86_MATCH_INTEL_FAM6_MODEL(ATOM_GOLDMONT,	PCI_DEVFN(13, 0)),
+	{}
+};
+
+static int p2sb_get_devfn(unsigned int *devfn)
+{
+	const struct x86_cpu_id *id;
+
+	id = x86_match_cpu(p2sb_cpu_ids);
+	if (!id)
+		return -ENODEV;
+
+	*devfn = (unsigned int)id->driver_data;
+	return 0;
+}
+
+static int p2sb_read_bar0(struct pci_dev *pdev, struct resource *mem)
+{
+	/* Copy resource from the first BAR of the device in question */
+	*mem = pdev->resource[0];
+	return 0;
+}
+
+static int p2sb_scan_and_read(struct pci_bus *bus, unsigned int devfn, struct resource *mem)
+{
+	struct pci_dev *pdev;
+	int ret;
+
+	pdev = pci_scan_single_device(bus, devfn);
+	if (!pdev)
+		return -ENODEV;
+
+	ret = p2sb_read_bar0(pdev, mem);
+
+	pci_stop_and_remove_bus_device(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
+ *
+ * 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.
+ *
+ * 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.
+ *
+ * Locking is handled by pci_rescan_remove_lock mutex.
+ *
+ * Return:
+ * 0 on success or appropriate errno value on error.
+ */
+int p2sb_bar(struct pci_bus *bus, unsigned int devfn, struct resource *mem)
+{
+	struct pci_dev *pdev_p2sb;
+	unsigned int devfn_p2sb;
+	u32 value = P2SBC_HIDE;
+	int ret;
+
+	/* Get devfn for P2SB device itself */
+	ret = p2sb_get_devfn(&devfn_p2sb);
+	if (ret)
+		return ret;
+
+	/* if @bus is NULL, use bus 0 in domain 0 */
+	bus = bus ?: pci_find_bus(0, 0);
+
+	/*
+	 * Prevent concurrent PCI bus scan from seeing the P2SB device and
+	 * removing via sysfs while it is temporarily exposed.
+	 */
+	pci_lock_rescan_remove();
+
+	/* Unhide the P2SB device, if needed */
+	pci_bus_read_config_dword(bus, devfn_p2sb, P2SBC, &value);
+	if (value & P2SBC_HIDE)
+		pci_bus_write_config_dword(bus, devfn_p2sb, P2SBC, 0);
+
+	pdev_p2sb = pci_scan_single_device(bus, devfn_p2sb);
+	if (devfn)
+		ret = p2sb_scan_and_read(bus, devfn, mem);
+	else
+		ret = p2sb_read_bar0(pdev_p2sb, mem);
+	pci_stop_and_remove_bus_device(pdev_p2sb);
+
+	/* Hide the P2SB device, if it was hidden */
+	if (value & P2SBC_HIDE)
+		pci_bus_write_config_dword(bus, devfn_p2sb, P2SBC, P2SBC_HIDE);
+
+	pci_unlock_rescan_remove();
+
+	if (ret)
+		return ret;
+
+	if (mem->flags == 0)
+		return -ENODEV;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(p2sb_bar);
diff --git a/include/linux/platform_data/x86/p2sb.h b/include/linux/platform_data/x86/p2sb.h
new file mode 100644
index 000000000000..a1d5fddc8f13
--- /dev/null
+++ b/include/linux/platform_data/x86/p2sb.h
@@ -0,0 +1,28 @@ 
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Primary to Sideband (P2SB) bridge access support
+ */
+
+#ifndef _PLATFORM_DATA_X86_P2SB_H
+#define _PLATFORM_DATA_X86_P2SB_H
+
+#include <linux/errno.h>
+#include <linux/kconfig.h>
+
+struct pci_bus;
+struct resource;
+
+#if IS_BUILTIN(CONFIG_P2SB)
+
+int p2sb_bar(struct pci_bus *bus, unsigned int devfn, struct resource *mem);
+
+#else /* CONFIG_P2SB */
+
+static inline int p2sb_bar(struct pci_bus *bus, unsigned int devfn, struct resource *mem)
+{
+	return -ENODEV;
+}
+
+#endif /* CONFIG_P2SB is not set */
+
+#endif /* _PLATFORM_DATA_X86_P2SB_H */