cxl/core: Check physical address before mapping it in devm_cxl_iomap_block()

The physical base address of a CXL range can be invalid and is then
set to CXL_RESOURCE_NONE. In general software shall prevent such
situations, but it is hard to proof this may never happen. E.g. in
add_port_attach_ep() there this the following:

      component_reg_phys = find_component_registers(uport_dev);
      port = devm_cxl_add_port(&parent_port->dev, uport_dev,
              component_reg_phys, parent_dport);

find_component_registers() and subsequent functions (e.g.
cxl_regmap_to_base()) may return CXL_RESOURCE_NONE. But it is written
to port without any further check in cxl_port_alloc():

      port->component_reg_phys = component_reg_phys;

It is then later directly used in devm_cxl_setup_hdm() to map io
ranges with devm_cxl_iomap_block(). Just an example...

Check this condition. Also do not fail silently like an ioremap()
failure, use a WARN_ON_ONCE() for it.
Signed-off-by: Robert Richter <rrichter@amd.com>
Link: https://lore.kernel.org/r/20221018132341.76259-3-rrichter@amd.comSigned-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/cxl/core/regs.c

@@ -167,6 +167,9 @@ void __iomem *devm_cxl_iomap_block(struct device *dev, resource_size_t addr,
 	void __iomem *ret_val;
 	struct resource *res;
 
+	if (WARN_ON_ONCE(addr == CXL_RESOURCE_NONE))
+		return NULL;
+
 	res = devm_request_mem_region(dev, addr, length, dev_name(dev));
 	if (!res) {
 		resource_size_t end = addr + length - 1;