[PATCH v2 1/6] cxl/port: Fix CXL port initialization order when the subsystem is built-in

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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 and that if cxl_acpi wins
the race cxl_mem will find the enabled CXL root ports it needs and if
cxl_acpi loses the race it will retrigger cxl_mem to attach via
cxl_bus_rescan(). That 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 object appears
before the cxl_acpi object in the Makefile.

Fix up the order to prevent initialization failures, and make sure that
cxl_port is built-in if cxl_acpi is also built-in.

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@xxxxxxxxxx>
Closes: http://lore.kernel.org/20241004212504.1246-1-gourry@xxxxxxxxxx
Tested-by: Gregory Price <gourry@xxxxxxxxxx>
Fixes: 8dd2bc0f8e02 ("cxl/mem: Add the cxl_mem driver")
Cc: <stable@xxxxxxxxxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: Jonathan Cameron <jonathan.cameron@xxxxxxxxxx>
Cc: Dave Jiang <dave.jiang@xxxxxxxxx>
Cc: Alison Schofield <alison.schofield@xxxxxxxxx>
Cc: Vishal Verma <vishal.l.verma@xxxxxxxxx>
Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
 drivers/cxl/Kconfig  |    1 +
 drivers/cxl/Makefile |   20 ++++++++++++++------
 2 files changed, 15 insertions(+), 6 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





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