[PATCH] arm64: PCI: Enable SMC conduit

[Jeremy Linton]

Given that most arm64 platform's PCI implementations needs quirks
to deal with problematic config accesses, this is a good place to
apply a firmware abstraction. The ARM PCI SMMCCC spec details a
standard SMC conduit designed to provide a simple PCI config
accessor. This specification enhances the existing ACPI/PCI
abstraction and expects power, config, etc functionality is handled
by the platform. It also is very explicit that the resulting config
space registers must behave as is specified by the pci specification.

Lets hook the normal ACPI/PCI config path, and when we detect
missing MADT data, attempt to probe the SMC conduit. If the conduit
exists and responds for the requested segment number (provided by the
ACPI namespace) attach a custom pci_ecam_ops which redirects
all config read/write requests to the firmware.

This patch is based on the Arm PCI Config space access document @
https://developer.arm.com/documentation/den0115/latest

Signed-off-by: Jeremy Linton <jeremy.linton@xxxxxxx>
---
 arch/arm64/kernel/pci.c   | 87 +++++++++++++++++++++++++++++++++++++++
 include/linux/arm-smccc.h | 26 ++++++++++++
 2 files changed, 113 insertions(+)

diff --git a/arch/arm64/kernel/pci.c b/arch/arm64/kernel/pci.c
index 1006ed2d7c60..56d3773aaa25 100644
--- a/arch/arm64/kernel/pci.c
+++ b/arch/arm64/kernel/pci.c
@@ -7,6 +7,7 @@
  */
 
 #include <linux/acpi.h>
+#include <linux/arm-smccc.h>
 #include <linux/init.h>
 #include <linux/io.h>
 #include <linux/kernel.h>
@@ -107,6 +108,90 @@ static int pci_acpi_root_prepare_resources(struct acpi_pci_root_info *ci)
 	return status;
 }
 
+static int smccc_pcie_check_conduit(u16 seg)
+{
+	struct arm_smccc_res res;
+
+	if (arm_smccc_1_1_get_conduit() == SMCCC_CONDUIT_NONE)
+		return -EOPNOTSUPP;
+
+	arm_smccc_smc(SMCCC_PCI_VERSION, 0, 0, 0, 0, 0, 0, 0, &res);
+	if ((int)res.a0 < 0)
+		return -EOPNOTSUPP;
+
+	arm_smccc_smc(SMCCC_PCI_SEG_INFO, seg, 0, 0, 0, 0, 0, 0, &res);
+	if ((int)res.a0 < 0)
+		return -EOPNOTSUPP;
+
+	pr_info("PCI: SMC conduit attached to segment %d\n", seg);
+
+	return 0;
+}
+
+static int smccc_pcie_config_read(struct pci_bus *bus, unsigned int devfn,
+				  int where, int size, u32 *val)
+{
+	struct arm_smccc_res res;
+
+	devfn |= bus->number << 8;
+	devfn |= bus->domain_nr << 16;
+
+	arm_smccc_smc(SMCCC_PCI_READ, devfn, where, size, 0, 0, 0, 0, &res);
+	if (res.a0) {
+		*val = ~0;
+		return -PCIBIOS_BAD_REGISTER_NUMBER;
+	}
+
+	*val = res.a1;
+	return PCIBIOS_SUCCESSFUL;
+}
+
+static int smccc_pcie_config_write(struct pci_bus *bus, unsigned int devfn,
+				   int where, int size, u32 val)
+{
+	struct arm_smccc_res res;
+
+	devfn |= bus->number << 8;
+	devfn |= bus->domain_nr << 16;
+
+	arm_smccc_smc(SMCCC_PCI_WRITE, devfn, where, size, val, 0, 0, 0, &res);
+	if (res.a0)
+		return -PCIBIOS_BAD_REGISTER_NUMBER;
+
+	return PCIBIOS_SUCCESSFUL;
+}
+
+static const struct pci_ecam_ops smccc_pcie_ecam_ops = {
+	.bus_shift	= 8,
+	.pci_ops	= {
+		.read		= smccc_pcie_config_read,
+		.write		= smccc_pcie_config_write,
+	}
+};
+
+static struct pci_config_window *
+pci_acpi_setup_smccc_mapping(struct acpi_pci_root *root)
+{
+	struct device *dev = &root->device->dev;
+	struct resource *bus_res = &root->secondary;
+	struct pci_config_window *cfg;
+
+	cfg = kzalloc(sizeof(*cfg), GFP_KERNEL);
+	if (!cfg)
+		return ERR_PTR(-ENOMEM);
+
+	cfg->parent = dev;
+	cfg->ops = &smccc_pcie_ecam_ops;
+	cfg->busr.start = bus_res->start;
+	cfg->busr.end = bus_res->end;
+	cfg->busr.flags = IORESOURCE_BUS;
+
+	cfg->res.name = "PCI SMCCC";
+	if (cfg->ops->init)
+		cfg->ops->init(cfg);
+	return cfg;
+}
+
 /*
  * Lookup the bus range for the domain in MCFG, and set up config space
  * mapping.
@@ -125,6 +210,8 @@ pci_acpi_setup_ecam_mapping(struct acpi_pci_root *root)
 
 	ret = pci_mcfg_lookup(root, &cfgres, &ecam_ops);
 	if (ret) {
+		if (!smccc_pcie_check_conduit(seg))
+			return pci_acpi_setup_smccc_mapping(root);
 		dev_err(dev, "%04x:%pR ECAM region not found\n", seg, bus_res);
 		return NULL;
 	}
diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
index f860645f6512..327f52533c71 100644
--- a/include/linux/arm-smccc.h
+++ b/include/linux/arm-smccc.h
@@ -89,6 +89,32 @@
 
 #define SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED	1
 
+/* PCI ECAM conduit */
+#define SMCCC_PCI_VERSION						\
+	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,				\
+			   ARM_SMCCC_SMC_32,				\
+			   ARM_SMCCC_OWNER_STANDARD, 0x0130)
+
+#define SMCCC_PCI_FEATURES						\
+	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,				\
+			   ARM_SMCCC_SMC_32,				\
+			   ARM_SMCCC_OWNER_STANDARD, 0x0131)
+
+#define SMCCC_PCI_READ							\
+	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,				\
+			   ARM_SMCCC_SMC_32,				\
+			   ARM_SMCCC_OWNER_STANDARD, 0x0132)
+
+#define SMCCC_PCI_WRITE							\
+	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,				\
+			   ARM_SMCCC_SMC_32,				\
+			   ARM_SMCCC_OWNER_STANDARD, 0x0133)
+
+#define SMCCC_PCI_SEG_INFO						\
+	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,				\
+			   ARM_SMCCC_SMC_32,				\
+			   ARM_SMCCC_OWNER_STANDARD, 0x0134)
+
 /* Paravirtualised time calls (defined by ARM DEN0057A) */
 #define ARM_SMCCC_HV_PV_TIME_FEATURES				\
 	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,			\
-- 
2.26.2