cxl: Deprecate driver

The cxl driver is no longer actively maintained and we intend to remove it
in a future kernel release.

cxl has received minimal maintenance for several years, and is not
supported on the Power10 processor. We aren't aware of any users who are
likely to be using recent kernels.

Change its MAINTAINERS status to obsolete, update the sysfs ABI
documentation accordingly, add a warning message on device probe, change
the Kconfig options to label it as deprecated, and don't build it by
default.

Signed-off-by: Andrew Donnellan <[e-mail]>
Acked-by: Frederic Barrat <[e-mail]>
Signed-off-by: Madhavan Srinivasan <[e-mail]>
Link: https://patch.msgid.link/[e-mail]

Documentation/ABI/testing/sysfs-class-cxl Documentation/ABI/obsolete/sysfs-class-cxl

···
+The cxl driver is no longer maintained, and will be removed from the kernel in
+the near future.
+
 Please note that attributes that are shared between devices are stored in
 the directory pointed to by the symlink device/.
 For example, the real path of the attribute /sys/class/cxl/afu0.0s/irqs_max is

MAINTAINERS

···
 M:	Frederic Barrat <[e-mail]>
 M:	Andrew Donnellan <[e-mail]>
 L:	[e-mail]
-S:	Supported
-F:	Documentation/ABI/testing/sysfs-class-cxl
+S:	Obsolete
+F:	Documentation/ABI/obsolete/sysfs-class-cxl
 F:	Documentation/arch/powerpc/cxl.rst
 F:	arch/powerpc/platforms/powernv/pci-cxl.c
 F:	drivers/misc/cxl/

drivers/misc/cxl/Kconfig

···
 	select PPC_64S_HASH_MMU
 
 config CXL
-	tristate "Support for IBM Coherent Accelerators (CXL)"
+	tristate "Support for IBM Coherent Accelerators (CXL) (DEPRECATED)"
 	depends on PPC_POWERNV && PCI_MSI && EEH
 	select CXL_BASE
-	default m
 	help
+	  The cxl driver is deprecated and will be removed in a future
+	  kernel release.
+
 	  Select this option to enable driver support for IBM Coherent
 	  Accelerators (CXL).  CXL is otherwise known as Coherent Accelerator
 	  Processor Interface (CAPI).  CAPI allows accelerators in FPGAs to be

drivers/misc/cxl/of.c

···
 	int ret;
 	int slice = 0, slice_ok = 0;
 
+	dev_err_once(&pdev->dev, "DEPRECATION: cxl is deprecated and will be removed in a future kernel release\n");
+
 	pr_devel("in %s\n", __func__);
 
 	np = pdev->dev.of_node;

drivers/misc/cxl/pci.c

···
 	int slice;
 	int rc;
 
+	dev_err_once(&dev->dev, "DEPRECATED: cxl is deprecated and will be removed in a future kernel release\n");
+
 	if (cxl_pci_is_vphb_device(dev)) {
 		dev_dbg(&dev->dev, "cxl_init_adapter: Ignoring cxl vphb device\n");
 		return -ENODEV;