[PATCH] ACPI / ARM64: Get configuration base address of ECAM via ACPI MCFG table

[Dennis Chen <dennis.chen@xxxxxxx>]

This patch will fall back to ACPI MCFG table if _CBA method fails
to get the configuration base address of ECAM. Firmware on ARM
platform uses MCFG table instead of _CBA method. This is needed
to scan the PCIe root complex for ARM SoC.

Signed-off-by: Dennis Chen <dennis.chen@xxxxxxx>
---
 drivers/pci/pci-acpi.c | 102 ++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 97 insertions(+), 5 deletions(-)

diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
index 314a625..211b9d9 100644
--- a/drivers/pci/pci-acpi.c
+++ b/drivers/pci/pci-acpi.c
@@ -27,18 +27,110 @@ const u8 pci_acpi_dsm_uuid[] = {
 	0x91, 0x17, 0xea, 0x4d, 0x19, 0xc3, 0x43, 0x4d
 };
 
+static int __init acpi_mcfg_check_entry(struct acpi_table_mcfg *mcfg)
+{
+	if (mcfg->header.revision != 1) {
+		pr_err("invalid header revision:%d in ACPI MCFG table\n",
+			mcfg->header.revision);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static phys_addr_t __init acpi_get_mcfg_cba(u16 segment, u8 bus)
+{
+	struct acpi_table_header *table = NULL;
+	acpi_size tbl_size;
+	struct acpi_table_mcfg *mcfg = NULL;
+	struct acpi_mcfg_allocation *cfg_table, *cfg;
+	acpi_status status;
+	phys_addr_t cba = 0;
+	unsigned long i;
+	int entries;
+
+	if (acpi_disabled)
+		return 0;
+
+	status = acpi_get_table_with_size(ACPI_SIG_MCFG, 0, &table, &tbl_size);
+	if (ACPI_FAILURE(status)) {
+		const char *msg = acpi_format_exception(status);
+
+		pr_err("Failed to get MCFG table, %s\n", msg);
+		return 0;
+	}
+
+	if (table)
+		mcfg = (struct acpi_table_mcfg *)table;
+
+	entries = 0;
+	i = table->length - sizeof(struct acpi_table_mcfg);
+	while (i >= sizeof(struct acpi_mcfg_allocation)) {
+		entries++;
+		i -= sizeof(struct acpi_mcfg_allocation);
+	}
+	if (entries == 0) {
+		pr_err("ACPI MCFG table has no entries\n");
+		goto out;
+	}
+
+	cfg_table = (struct acpi_mcfg_allocation *) &mcfg[1];
+	for (i = 0; i < entries; i++) {
+		cfg = &cfg_table[i];
+		if (acpi_mcfg_check_entry(mcfg))
+			goto out;
+
+		if (cfg->pci_segment == segment &&
+			cfg->start_bus_number <= bus &&
+			bus <= cfg->end_bus_number) {
+			cba = (phys_addr_t)cfg->address;
+			goto out;
+		}
+	}
+out:
+	/*
+	 * acpi_get_table_with_size() creates MCFG table mapping that
+	 * should be released after parsing and before resuming boot
+	 */
+	early_acpi_os_unmap_memory(table, tbl_size);
+	return cba;
+}
+
 phys_addr_t acpi_pci_root_get_mcfg_addr(acpi_handle handle)
 {
 	acpi_status status = AE_NOT_EXIST;
-	unsigned long long mcfg_addr;
+	unsigned long long mcfg_addr, mcfg_seg, mcfg_bus;
+	u16 seg;
+	u8 bus;
+
+	if (!handle)
+		return 0;
 
-	if (handle)
-		status = acpi_evaluate_integer(handle, METHOD_NAME__CBA,
+	status = acpi_evaluate_integer(handle, METHOD_NAME__CBA,
 					       NULL, &mcfg_addr);
+	if (ACPI_SUCCESS(status))
+		return (phys_addr_t)mcfg_addr;
+
+	pr_info("ACPI: Falling back to acpi mcfg table\n");
+
+	/*
+	 * Fall back to MCFG table if _CBA failed:
+	 * get the mcfg_addr via ACPI MCFG table. PCI Firmware v3.2 spec: 4.1.2
+	 */
+	status = acpi_evaluate_integer(handle, METHOD_NAME__SEG,
+						NULL, &mcfg_seg);
 	if (ACPI_FAILURE(status))
-		return 0;
+		mcfg_seg = 0;
+
+	status = acpi_evaluate_integer(handle, METHOD_NAME__BBN,
+						NULL, &mcfg_bus);
+	if (ACPI_FAILURE(status))
+		mcfg_bus = 0;
+
+	seg = mcfg_seg & 0xFFFF;
+	bus = mcfg_bus & 0xFF;
 
-	return (phys_addr_t)mcfg_addr;
+	return acpi_get_mcfg_cba(seg, bus);
 }
 
 static acpi_status decode_type0_hpx_record(union acpi_object *record,
-- 
1.9.1

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