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 gourry@gourry.net Closes: http://lore.kernel.org/20241004212504.1246-1-gourry@gourry.net Tested-by: Gregory Price gourry@gourry.net Fixes: 8dd2bc0f8e02 ("cxl/mem: Add the cxl_mem driver") Cc: stable@vger.kernel.org Cc: Davidlohr Bueso dave@stgolabs.net Cc: Jonathan Cameron jonathan.cameron@huawei.com Cc: Dave Jiang dave.jiang@intel.com Cc: Alison Schofield alison.schofield@intel.com Cc: Vishal Verma vishal.l.verma@intel.com Cc: Ira Weiny ira.weiny@intel.com Reviewed-by: Jonathan Cameron Jonathan.Cameron@huawei.com Reviewed-by: Ira Weiny ira.weiny@intel.com Tested-by: Alejandro Lucero alucerop@amd.com Reviewed-by: Alejandro Lucero alucerop@amd.com Signed-off-by: Dan Williams dan.j.williams@intel.com --- 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(-)
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);