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

drivers/pci/controller/dwc/Kconfig

@@ -482,15 +482,21 @@ 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
@@ -498,11 +504,12 @@ config PCI_KEYSTONE_HOST
 	  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
+static int ks_pcie_init_id(struct keystone_pcie *ks_pcie)
-/*
- * 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)
 {
 	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>");