thunderbolt: Expose active parts of NVM even if upgrade is not supported

Ice Lake Thunderbolt controller NVM firmware is part of the BIOS image
which means it is not writable through the DMA port anymore. However, we
can still read it so we can keep nvm_version and active parts of NVM.
This way users still can find out the active NVM version and other
potentially useful information directly from Linux.

Signed-off-by: Mika Westerberg <[e-mail]>
Reviewed-by: Yehezkel Bernat <[e-mail]>
Tested-by: Mario Limonciello <[e-mail]>

drivers/thunderbolt/switch.c

···
 		nvm->active = nvm_dev;
 	}
 
-	nvm_dev = register_nvmem(sw, nvm->id, NVM_MAX_SIZE, false);
-	if (IS_ERR(nvm_dev)) {
-		ret = PTR_ERR(nvm_dev);
-		goto err_nvm_active;
+	if (!sw->no_nvm_upgrade) {
+		nvm_dev = register_nvmem(sw, nvm->id, NVM_MAX_SIZE, false);
+		if (IS_ERR(nvm_dev)) {
+			ret = PTR_ERR(nvm_dev);
+			goto err_nvm_active;
+		}
+		nvm->non_active = nvm_dev;
 	}
-	nvm->non_active = nvm_dev;
 
 	sw->nvm = nvm;
 	return 0;
···
 	if (!nvm->authenticating)
 		nvm_clear_auth_status(sw);
 
-	nvmem_unregister(nvm->non_active);
+	if (nvm->non_active)
+		nvmem_unregister(nvm->non_active);
 	if (nvm->active)
 		nvmem_unregister(nvm->active);
 	ida_simple_remove(&nvm_ida, nvm->id);
···
 		    sw->security_level == TB_SECURITY_SECURE)
 			return attr->mode;
 		return 0;
-	} else if (attr == &dev_attr_nvm_authenticate.attr ||
-		   attr == &dev_attr_nvm_version.attr) {
+	} else if (attr == &dev_attr_nvm_authenticate.attr) {
+		if (sw->dma_port && !sw->no_nvm_upgrade)
+			return attr->mode;
+		return 0;
+	} else if (attr == &dev_attr_nvm_version.attr) {
 		if (sw->dma_port)
 			return attr->mode;
 		return 0;
···
 		break;
 	}
 
-	if (sw->no_nvm_upgrade)
+	/* Root switch DMA port requires running firmware */
+	if (!tb_route(sw) && sw->config.enabled)
 		return 0;
 
 	sw->dma_port = dma_port_alloc(sw);
 	if (!sw->dma_port)
+		return 0;
+
+	if (sw->no_nvm_upgrade)
 		return 0;
 
 	/*