PCI: keystone: Add support to build as a loadable module

The 'pci-keystone.c' driver is the application/glue/wrapper driver for the
Designware PCIe Controllers on TI SoCs. Now that all of the helper APIs
that the 'pci-keystone.c' driver depends upon have been exported for use,
enable support to build the driver as a loadable module.

When building the driver as a module, the functions marked by the '__init'
keyword may be invoked after the init memory has been freed by the kernel.
This results will result in an exception of the form:

  Unable to handle kernel paging request at virtual address ...
  Mem abort info:
  ...
  pc : ks_pcie_host_init+0x0/0x540
  lr : dw_pcie_host_init+0x170/0x498
  ...
  ks_pcie_host_init+0x0/0x540 (P)
  ks_pcie_probe+0x728/0x84c
  platform_probe+0x5c/0x98
  really_probe+0xbc/0x29c
  __driver_probe_device+0x78/0x12c
  driver_probe_device+0xd8/0x15c

To address this, introduce a new function namely 'ks_pcie_init()' to
register the 'fault handler' while removing the '__init' keyword from
existing functions.

Note that hook_fault_code() is defined as '__init' function. Since the init
functions should never be called during runtime (after init memory freeing
stage), the driver is made as a built-in if CONFIG_ARM (where
hook_fault_code() is used) is selected.

Signed-off-by: Siddharth Vadapalli <s-vadapalli@ti.com>
[mani: added a note about hook_fault_code()]
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://patch.msgid.link/20251029080547.1253757-5-s-vadapalli@ti.com

Author: Siddharth-Vadapalli-at-TI

drivers/pci/controller/dwc/Kconfig

@@ -482,27 +482,34 @@ config PCI_DRA7XX_EP
 	  to enable device-specific features PCI_DRA7XX_EP must be selected.
 	  This uses the DesignWare core.
 
+# ARM32 platforms use hook_fault_code() and cannot support loadable module.
 config PCI_KEYSTONE
 	bool
 
+# On non-ARM32 platforms, loadable module can be supported.
+config PCI_KEYSTONE_TRISTATE
+	tristate
+
 config PCI_KEYSTONE_HOST
-	bool "TI Keystone PCIe controller (host mode)"
+	tristate "TI Keystone PCIe controller (host mode)"
 	depends on ARCH_KEYSTONE || ARCH_K3 || COMPILE_TEST
 	depends on PCI_MSI
 	select PCIE_DW_HOST
-	select PCI_KEYSTONE
+	select PCI_KEYSTONE if ARM
+	select PCI_KEYSTONE_TRISTATE if !ARM
 	help
 	  Enables support for the PCIe controller in the Keystone SoC to
 	  work in host mode. The PCI controller on Keystone is based on
 	  DesignWare hardware and therefore the driver re-uses the
 	  DesignWare core functions to implement the driver.
 
 config PCI_KEYSTONE_EP
-	bool "TI Keystone PCIe controller (endpoint mode)"
+	tristate "TI Keystone PCIe controller (endpoint mode)"
 	depends on ARCH_KEYSTONE || ARCH_K3 || COMPILE_TEST
 	depends on PCI_ENDPOINT
 	select PCIE_DW_EP
-	select PCI_KEYSTONE
+	select PCI_KEYSTONE if ARM
+	select PCI_KEYSTONE_TRISTATE if !ARM
 	help
 	  Enables support for the PCIe controller in the Keystone SoC to
 	  work in endpoint mode. The PCI controller on Keystone is based

drivers/pci/controller/dwc/Makefile

@@ -11,7 +11,10 @@ obj-$(CONFIG_PCI_EXYNOS) += pci-exynos.o
 obj-$(CONFIG_PCIE_FU740) += pcie-fu740.o
 obj-$(CONFIG_PCI_IMX6) += pci-imx6.o
 obj-$(CONFIG_PCIE_SPEAR13XX) += pcie-spear13xx.o
+# ARM32 platforms use hook_fault_code() and cannot support loadable module.
 obj-$(CONFIG_PCI_KEYSTONE) += pci-keystone.o
+# On non-ARM32 platforms, loadable module can be supported.
+obj-$(CONFIG_PCI_KEYSTONE_TRISTATE) += pci-keystone.o
 obj-$(CONFIG_PCI_LAYERSCAPE) += pci-layerscape.o
 obj-$(CONFIG_PCI_LAYERSCAPE_EP) += pci-layerscape-ep.o
 obj-$(CONFIG_PCIE_QCOM_COMMON) += pcie-qcom-common.o

drivers/pci/controller/dwc/pci-keystone.c

@@ -17,6 +17,7 @@
 #include <linux/irqchip/chained_irq.h>
 #include <linux/irqdomain.h>
 #include <linux/mfd/syscon.h>
+#include <linux/module.h>
 #include <linux/msi.h>
 #include <linux/of.h>
 #include <linux/of_irq.h>
@@ -777,29 +778,7 @@ static int ks_pcie_config_intx_irq(struct keystone_pcie *ks_pcie)
 	return ret;
 }
 
-#ifdef CONFIG_ARM
-/*
- * When a PCI device does not exist during config cycles, keystone host
- * gets a bus error instead of returning 0xffffffff (PCI_ERROR_RESPONSE).
- * This handler always returns 0 for this kind of fault.
- */
-static int ks_pcie_fault(unsigned long addr, unsigned int fsr,
-			 struct pt_regs *regs)
-{
-	unsigned long instr = *(unsigned long *) instruction_pointer(regs);
-
-	if ((instr & 0x0e100090) == 0x00100090) {
-		int reg = (instr >> 12) & 15;
-
-		regs->uregs[reg] = -1;
-		regs->ARM_pc += 4;
-	}
-
-	return 0;
-}
-#endif
-
-static int __init ks_pcie_init_id(struct keystone_pcie *ks_pcie)
+static int ks_pcie_init_id(struct keystone_pcie *ks_pcie)
 {
 	int ret;
 	unsigned int id;
@@ -831,7 +810,7 @@ static int __init ks_pcie_init_id(struct keystone_pcie *ks_pcie)
 	return 0;
 }
 
-static int __init ks_pcie_host_init(struct dw_pcie_rp *pp)
+static int ks_pcie_host_init(struct dw_pcie_rp *pp)
 {
 	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
 	struct keystone_pcie *ks_pcie = to_keystone_pcie(pci);
@@ -861,15 +840,6 @@ static int __init ks_pcie_host_init(struct dw_pcie_rp *pp)
 	if (ret < 0)
 		return ret;
 
-#ifdef CONFIG_ARM
-	/*
-	 * PCIe access errors that result into OCP errors are caught by ARM as
-	 * "External aborts"
-	 */
-	hook_fault_code(17, ks_pcie_fault, SIGBUS, 0,
-			"Asynchronous external abort");
-#endif
-
 	return 0;
 }
 
@@ -1134,6 +1104,7 @@ static const struct of_device_id ks_pcie_of_match[] = {
 	},
 	{ },
 };
+MODULE_DEVICE_TABLE(of, ks_pcie_of_match);
 
 static int ks_pcie_probe(struct platform_device *pdev)
 {
@@ -1381,4 +1352,45 @@ static struct platform_driver ks_pcie_driver = {
 		.of_match_table = ks_pcie_of_match,
 	},
 };
+
+#ifdef CONFIG_ARM
+/*
+ * When a PCI device does not exist during config cycles, keystone host
+ * gets a bus error instead of returning 0xffffffff (PCI_ERROR_RESPONSE).
+ * This handler always returns 0 for this kind of fault.
+ */
+static int ks_pcie_fault(unsigned long addr, unsigned int fsr,
+			 struct pt_regs *regs)
+{
+	unsigned long instr = *(unsigned long *)instruction_pointer(regs);
+
+	if ((instr & 0x0e100090) == 0x00100090) {
+		int reg = (instr >> 12) & 15;
+
+		regs->uregs[reg] = -1;
+		regs->ARM_pc += 4;
+	}
+
+	return 0;
+}
+
+static int __init ks_pcie_init(void)
+{
+	/*
+	 * PCIe access errors that result into OCP errors are caught by ARM as
+	 * "External aborts"
+	 */
+	if (of_find_matching_node(NULL, ks_pcie_of_match))
+		hook_fault_code(17, ks_pcie_fault, SIGBUS, 0,
+				"Asynchronous external abort");
+
+	return platform_driver_register(&ks_pcie_driver);
+}
+device_initcall(ks_pcie_init);
+#else
 builtin_platform_driver(ks_pcie_driver);
+#endif
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("PCIe controller driver for Texas Instruments Keystone SoCs");
+MODULE_AUTHOR("Murali Karicheri <m-karicheri2@ti.com>");