PCI: Introduce PCI bridge emulated config space common logic

Some PCI host controllers do not expose a configuration space for the
root port PCI bridge. Due to this, the Marvell Armada 370/38x/XP PCI
controller driver (pci-mvebu) emulates a root port PCI bridge
configuration space, and uses that to (among other things) dynamically
create the memory windows that correspond to the PCI MEM and I/O
regions.

Since we now need to add a very similar logic for the Marvell Armada
37xx PCI controller driver (pci-aardvark), instead of duplicating the
code, we create in this commit a common logic called pci-bridge-emul.

The idea of this logic is to emulate a root port PCI bridge
configuration space by providing configuration space read/write
operations, and faking behind the scenes the configuration space of a
PCI bridge. A PCI host controller driver simply has to call
pci_bridge_emul_conf_read() and pci_bridge_emul_conf_write() to
read/write the configuration space of the bridge.

By default, the PCI bridge configuration space is simply emulated by a
chunk of memory, but the PCI host controller can override the behavior
of the read and write operations on a per-register basis to do
additional actions if needed. We take care of complying with the
behavior of the PCI configuration space registers in terms of bits
that are read-write, read-only, reserved and write-1-to-clear.
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Russell King <rmk+kernel@armlinux.org.uk>

drivers/pci/Kconfig

@@ -98,6 +98,9 @@ config PCI_ECAM
 config PCI_LOCKLESS_CONFIG
 	bool
 
+config PCI_BRIDGE_EMUL
+	bool
+
 config PCI_IOV
 	bool "PCI IOV support"
 	depends on PCI

drivers/pci/Makefile

@@ -19,6 +19,7 @@ obj-$(CONFIG_HOTPLUG_PCI)	+= hotplug/
 obj-$(CONFIG_PCI_MSI)		+= msi.o
 obj-$(CONFIG_PCI_ATS)		+= ats.o
 obj-$(CONFIG_PCI_IOV)		+= iov.o
+obj-$(CONFIG_PCI_BRIDGE_EMUL)	+= pci-bridge-emul.o
 obj-$(CONFIG_ACPI)		+= pci-acpi.o
 obj-$(CONFIG_PCI_LABEL)		+= pci-label.o
 obj-$(CONFIG_X86_INTEL_MID)	+= pci-mid.o

drivers/pci/pci-bridge-emul.h

+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __PCI_BRIDGE_EMUL_H__
+#define __PCI_BRIDGE_EMUL_H__
+
+#include <linux/kernel.h>
+
+/* PCI configuration space of a PCI-to-PCI bridge. */
+struct pci_bridge_emul_conf {
+	u16 vendor;
+	u16 device;
+	u16 command;
+	u16 status;
+	u32 class_revision;
+	u8 cache_line_size;
+	u8 latency_timer;
+	u8 header_type;
+	u8 bist;
+	u32 bar[2];
+	u8 primary_bus;
+	u8 secondary_bus;
+	u8 subordinate_bus;
+	u8 secondary_latency_timer;
+	u8 iobase;
+	u8 iolimit;
+	u16 secondary_status;
+	u16 membase;
+	u16 memlimit;
+	u16 pref_mem_base;
+	u16 pref_mem_limit;
+	u32 prefbaseupper;
+	u32 preflimitupper;
+	u16 iobaseupper;
+	u16 iolimitupper;
+	u8 capabilities_pointer;
+	u8 reserve[3];
+	u32 romaddr;
+	u8 intline;
+	u8 intpin;
+	u16 bridgectrl;
+};
+
+/* PCI configuration space of the PCIe capabilities */
+struct pci_bridge_emul_pcie_conf {
+	u8 cap_id;
+	u8 next;
+	u16 cap;
+	u32 devcap;
+	u16 devctl;
+	u16 devsta;
+	u32 lnkcap;
+	u16 lnkctl;
+	u16 lnksta;
+	u32 slotcap;
+	u16 slotctl;
+	u16 slotsta;
+	u16 rootctl;
+	u16 rsvd;
+	u32 rootsta;
+	u32 devcap2;
+	u16 devctl2;
+	u16 devsta2;
+	u32 lnkcap2;
+	u16 lnkctl2;
+	u16 lnksta2;
+	u32 slotcap2;
+	u16 slotctl2;
+	u16 slotsta2;
+};
+
+struct pci_bridge_emul;
+
+typedef enum { PCI_BRIDGE_EMUL_HANDLED,
+	       PCI_BRIDGE_EMUL_NOT_HANDLED } pci_bridge_emul_read_status_t;
+
+struct pci_bridge_emul_ops {
+	/*
+	 * Called when reading from the regular PCI bridge
+	 * configuration space. Return PCI_BRIDGE_EMUL_HANDLED when the
+	 * operation has handled the read operation and filled in the
+	 * *value, or PCI_BRIDGE_EMUL_NOT_HANDLED when the read should
+	 * be emulated by the common code by reading from the
+	 * in-memory copy of the configuration space.
+	 */
+	pci_bridge_emul_read_status_t (*read_base)(struct pci_bridge_emul *bridge,
+						   int reg, u32 *value);
+
+	/*
+	 * Same as ->read_base(), except it is for reading from the
+	 * PCIe capability configuration space.
+	 */
+	pci_bridge_emul_read_status_t (*read_pcie)(struct pci_bridge_emul *bridge,
+						   int reg, u32 *value);
+	/*
+	 * Called when writing to the regular PCI bridge configuration
+	 * space. old is the current value, new is the new value being
+	 * written, and mask indicates which parts of the value are
+	 * being changed.
+	 */
+	void (*write_base)(struct pci_bridge_emul *bridge, int reg,
+			   u32 old, u32 new, u32 mask);
+
+	/*
+	 * Same as ->write_base(), except it is for writing from the
+	 * PCIe capability configuration space.
+	 */
+	void (*write_pcie)(struct pci_bridge_emul *bridge, int reg,
+			   u32 old, u32 new, u32 mask);
+};
+
+struct pci_bridge_emul {
+	struct pci_bridge_emul_conf conf;
+	struct pci_bridge_emul_pcie_conf pcie_conf;
+	struct pci_bridge_emul_ops *ops;
+	void *data;
+	bool has_pcie;
+};
+
+void pci_bridge_emul_init(struct pci_bridge_emul *bridge);
+int pci_bridge_emul_conf_read(struct pci_bridge_emul *bridge, int where,
+			      int size, u32 *value);
+int pci_bridge_emul_conf_write(struct pci_bridge_emul *bridge, int where,
+			       int size, u32 value);
+
+#endif /* __PCI_BRIDGE_EMUL_H__ */