[v3,1/6] cxl/port: Fix CXL port initialization order when the subsystem is built-in

Commit Message

Dan Williams Oct. 25, 2024, 7:32 p.m. UTC

When the CXL subsystem is built-in the module init order is determined
by Makefile order. That order violates expectations. The expectation is
that cxl_acpi and cxl_mem can race to attach. If cxl_acpi wins the race,
cxl_mem will find the enabled CXL root ports it needs. If cxl_acpi loses
the race it will retrigger cxl_mem to attach via cxl_bus_rescan(). That
flow only works if cxl_acpi can assume ports are enabled immediately
upon cxl_acpi_probe() return. That in turn can only happen in the
CONFIG_CXL_ACPI=y case if the cxl_port driver is registered before
cxl_acpi_probe() runs.

Fix up the order to prevent initialization failures. Ensure that
cxl_port is built-in when cxl_acpi is also built-in, arrange for
Makefile order to resolve the subsys_initcall() order of cxl_port and
cxl_acpi, and arrange for Makefile order to resolve the
device_initcall() (module_init()) order of the remaining objects.

As for what contributed to this not being found earlier, the CXL
regression environment, cxl_test, builds all CXL functionality as a
module to allow to symbol mocking and other dynamic reload tests.  As a
result there is no regression coverage for the built-in case.

Reported-by: Gregory Price <[e-mail]>
Closes: http://lore.kernel.org/[e-mail]
Tested-by: Gregory Price <[e-mail]>
Fixes: 8dd2bc0f8e02 ("cxl/mem: Add the cxl_mem driver")
Cc: [e-mail]
Cc: Davidlohr Bueso <[e-mail]>
Cc: Jonathan Cameron <[e-mail]>
Cc: Dave Jiang <[e-mail]>
Cc: Alison Schofield <[e-mail]>
Cc: Vishal Verma <[e-mail]>
Cc: Ira Weiny <[e-mail]>
Reviewed-by: Jonathan Cameron <[e-mail]>
Reviewed-by: Ira Weiny <[e-mail]>
Tested-by: Alejandro Lucero <[e-mail]>
Reviewed-by: Alejandro Lucero <[e-mail]>
Signed-off-by: Dan Williams <[e-mail]>
---
Changes since v2
- Partial re-roll patch1 to address comments and collect tags
- Move cxl_port to subsys_initcall, clarify changelog (Alejandro)

 drivers/cxl/Kconfig  |    1 +
 drivers/cxl/Makefile |   20 ++++++++++++++------
 drivers/cxl/port.c   |   17 ++++++++++++++++-
 3 files changed, 31 insertions(+), 7 deletions(-)

Patch

diff --git a/drivers/cxl/Kconfig b/drivers/cxl/Kconfig
index 29c192f20082..876469e23f7a 100644
--- a/drivers/cxl/Kconfig
+++ b/drivers/cxl/Kconfig
@@ -60,6 +60,7 @@  config CXL_ACPI
 	default CXL_BUS
 	select ACPI_TABLE_LIB
 	select ACPI_HMAT
+	select CXL_PORT
 	help
 	  Enable support for host managed device memory (HDM) resources
 	  published by a platform's ACPI CXL memory layout description.  See
diff --git a/drivers/cxl/Makefile b/drivers/cxl/Makefile
index db321f48ba52..2caa90fa4bf2 100644
--- a/drivers/cxl/Makefile
+++ b/drivers/cxl/Makefile
@@ -1,13 +1,21 @@ 
 # SPDX-License-Identifier: GPL-2.0
+
+# Order is important here for the built-in case:
+# - 'core' first for fundamental init
+# - 'port' before platform root drivers like 'acpi' so that CXL-root ports
+#   are immediately enabled
+# - 'mem' and 'pmem' before endpoint drivers so that memdevs are
+#   immediately enabled
+# - 'pci' last, also mirrors the hardware enumeration hierarchy
 obj-y += core/
-obj-$(CONFIG_CXL_PCI) += cxl_pci.o
-obj-$(CONFIG_CXL_MEM) += cxl_mem.o
+obj-$(CONFIG_CXL_PORT) += cxl_port.o
 obj-$(CONFIG_CXL_ACPI) += cxl_acpi.o
 obj-$(CONFIG_CXL_PMEM) += cxl_pmem.o
-obj-$(CONFIG_CXL_PORT) += cxl_port.o
+obj-$(CONFIG_CXL_MEM) += cxl_mem.o
+obj-$(CONFIG_CXL_PCI) += cxl_pci.o
 
-cxl_mem-y := mem.o
-cxl_pci-y := pci.o
+cxl_port-y := port.o
 cxl_acpi-y := acpi.o
 cxl_pmem-y := pmem.o security.o
-cxl_port-y := port.o
+cxl_mem-y := mem.o
+cxl_pci-y := pci.o
diff --git a/drivers/cxl/port.c b/drivers/cxl/port.c
index 861dde65768f..9dc394295e1f 100644
--- a/drivers/cxl/port.c
+++ b/drivers/cxl/port.c
@@ -208,7 +208,22 @@  static struct cxl_driver cxl_port_driver = {
 	},
 };
 
-module_cxl_driver(cxl_port_driver);
+static int __init cxl_port_init(void)
+{
+	return cxl_driver_register(&cxl_port_driver);
+}
+/*
+ * Be ready to immediately enable ports emitted by the platform CXL root
+ * (e.g. cxl_acpi) when CONFIG_CXL_PORT=y.
+ */
+subsys_initcall(cxl_port_init);
+
+static void __exit cxl_port_exit(void)
+{
+	cxl_driver_unregister(&cxl_port_driver);
+}
+module_exit(cxl_port_exit);
+
 MODULE_DESCRIPTION("CXL: Port enumeration and services");
 MODULE_LICENSE("GPL v2");
 MODULE_IMPORT_NS(CXL);