cxl/pci: Fix disabling memory if DVSEC CXL Range does not match a CFMWS window

The Linux CXL subsystem is built on the assumption that HPA == SPA.
That is, the host physical address (HPA) the HDM decoder registers are
programmed with are system physical addresses (SPA).

During HDM decoder setup, the DVSEC CXL range registers (cxl-3.1,
8.1.3.8) are checked if the memory is enabled and the CXL range is in
a HPA window that is described in a CFMWS structure of the CXL host
bridge (cxl-3.1, 9.18.1.3).

Now, if the HPA is not an SPA, the CXL range does not match a CFMWS
window and the CXL memory range will be disabled then. The HDM decoder
stops working which causes system memory being disabled and further a
system hang during HDM decoder initialization, typically when a CXL
enabled kernel boots.

Prevent a system hang and do not disable the HDM decoder if the
decoder's CXL range is not found in a CFMWS window.

Note the change only fixes a hardware hang, but does not implement
HPA/SPA translation. Support for this can be added in a follow on
patch series.

Signed-off-by: Robert Richter <rrichter@amd.com>
Fixes: 34e37b4 ("cxl/port: Enable HDM Capability after validating DVSEC Ranges")
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20240216160113.407141-1-rrichter@amd.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Author: Robert Richter

drivers/cxl/core/pci.c

@@ -477,9 +477,9 @@ int cxl_hdm_decode_init(struct cxl_dev_state *cxlds, struct cxl_hdm *cxlhdm,
 		allowed++;
 	}
 
-	if (!allowed) {
-		cxl_set_mem_enable(cxlds, 0);
-		info->mem_enabled = 0;
+	if (!allowed && info->mem_enabled) {
+		dev_err(dev, "Range register decodes outside platform defined CXL ranges.\n");
+		return -ENXIO;
 	}
 
 	/*