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 <mika.westerberg@linux.intel.com>
Reviewed-by: Yehezkel Bernat <YehezkelShB@gmail.com>
Tested-by: Mario Limonciello <mario.limonciello@dell.com>

drivers/thunderbolt/switch.c

@@ -364,12 +364,14 @@ static int tb_switch_nvm_add(struct tb_switch *sw)
 		nvm->active = nvm_dev;
 	}
 
+	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;
+	}
 
 	sw->nvm = nvm;
 	return 0;
@@ -398,6 +400,7 @@ static void tb_switch_nvm_remove(struct tb_switch *sw)
 	if (!nvm->authenticating)
 		nvm_clear_auth_status(sw);
 
+	if (nvm->non_active)
 		nvmem_unregister(nvm->non_active);
 	if (nvm->active)
 		nvmem_unregister(nvm->active);
@@ -1355,8 +1358,11 @@ static umode_t switch_attr_is_visible(struct kobject *kobj,
 		    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;
@@ -1707,13 +1713,17 @@ static int tb_switch_add_dma_port(struct tb_switch *sw)
 		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;
+
 	/*
 	 * Check status of the previous flash authentication. If there
 	 * is one we need to power cycle the switch in any case to make