ACPI: RISC-V: Implement PCI related functionality

Replace the dummy implementation for PCI related functions with actual
implementation. This needs ECAM and MCFG CONFIG options to be enabled
for RISC-V.

Signed-off-by: Sunil V L <[e-mail]>
Tested-by: Björn Töpel <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Rafael J. Wysocki <[e-mail]>

arch/riscv/Kconfig

···
 config RISCV
 	def_bool y
 	select ACPI_GENERIC_GSI if ACPI
+	select ACPI_MCFG if (ACPI && PCI)
 	select ACPI_PPTT if ACPI
 	select ACPI_REDUCED_HARDWARE_ONLY if ACPI
 	select ACPI_SPCR_TABLE if ACPI
···
 	select OF_EARLY_FLATTREE
 	select OF_IRQ
 	select PCI_DOMAINS_GENERIC if PCI
+	select PCI_ECAM if (ACPI && PCI)
 	select PCI_MSI if PCI
 	select RISCV_ALTERNATIVE if !XIP_KERNEL
 	select RISCV_APLIC

arch/riscv/kernel/acpi.c

···
 #ifdef CONFIG_PCI
 
 /*
- * These interfaces are defined just to enable building ACPI core.
- * TODO: Update it with actual implementation when external interrupt
- * controller support is added in RISC-V ACPI.
+ * raw_pci_read/write - Platform-specific PCI config space access.
  */
-int raw_pci_read(unsigned int domain, unsigned int bus, unsigned int devfn,
-		 int reg, int len, u32 *val)
+int raw_pci_read(unsigned int domain, unsigned int bus,
+		 unsigned int devfn, int reg, int len, u32 *val)
 {
-	return PCIBIOS_DEVICE_NOT_FOUND;
+	struct pci_bus *b = pci_find_bus(domain, bus);
+
+	if (!b)
+		return PCIBIOS_DEVICE_NOT_FOUND;
+	return b->ops->read(b, devfn, reg, len, val);
 }
 
-int raw_pci_write(unsigned int domain, unsigned int bus, unsigned int devfn,
-		  int reg, int len, u32 val)
+int raw_pci_write(unsigned int domain, unsigned int bus,
+		  unsigned int devfn, int reg, int len, u32 val)
 {
-	return PCIBIOS_DEVICE_NOT_FOUND;
+	struct pci_bus *b = pci_find_bus(domain, bus);
+
+	if (!b)
+		return PCIBIOS_DEVICE_NOT_FOUND;
+	return b->ops->write(b, devfn, reg, len, val);
 }
 
-int acpi_pci_bus_find_domain_nr(struct pci_bus *bus)
-{
-	return -1;
-}
-
-struct pci_bus *pci_acpi_scan_root(struct acpi_pci_root *root)
-{
-	return NULL;
-}
 #endif	/* CONFIG_PCI */

drivers/pci/pci-acpi.c

···
 }
 arch_initcall(acpi_pci_init);
 
-#if defined(CONFIG_ARM64)
+#if defined(CONFIG_ARM64) || defined(CONFIG_RISCV)
 
 /*
  * Try to assign the IRQ number when probing a new device