iommu/mediatek: Fix NULL pointer deference in mtk_iommu_device_group

Currently, mtk_iommu calls during probe iommu_device_register before
the hw_list from driver data is initialized. Since iommu probing issue
fix, it leads to NULL pointer dereference in mtk_iommu_device_group when
hw_list is accessed with list_first_entry (not null safe).

So, change the call order to ensure iommu_device_register is called
after the driver data are initialized.

Fixes: 9e3a2a6 ("iommu/mediatek: Adapt sharing and non-sharing pgtable case")
Fixes: bcb81ac ("iommu: Get DT/ACPI parsing into the proper probe path")
Reviewed-by: Yong Wu <yong.wu@mediatek.com>
Tested-by: Chen-Yu Tsai <wenst@chromium.org> # MT8183 Juniper, MT8186 Tentacruel
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Tested-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Louis-Alexis Eyraud <louisalexis.eyraud@collabora.com>
Link: https://lore.kernel.org/r/20250403-fix-mtk-iommu-error-v2-1-fe8b18f8b0a8@collabora.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>

Author: laeyraud

drivers/iommu/mtk_iommu.c

@@ -1372,15 +1372,6 @@ static int mtk_iommu_probe(struct platform_device *pdev)
 	platform_set_drvdata(pdev, data);
 	mutex_init(&data->mutex);
 
-	ret = iommu_device_sysfs_add(&data->iommu, dev, NULL,
-				     "mtk-iommu.%pa", &ioaddr);
-	if (ret)
-		goto out_link_remove;
-
-	ret = iommu_device_register(&data->iommu, &mtk_iommu_ops, dev);
-	if (ret)
-		goto out_sysfs_remove;
-
 	if (MTK_IOMMU_HAS_FLAG(data->plat_data, SHARE_PGTABLE)) {
 		list_add_tail(&data->list, data->plat_data->hw_list);
 		data->hw_list = data->plat_data->hw_list;
@@ -1390,19 +1381,28 @@ static int mtk_iommu_probe(struct platform_device *pdev)
 		data->hw_list = &data->hw_list_head;
 	}
 
+	ret = iommu_device_sysfs_add(&data->iommu, dev, NULL,
+				     "mtk-iommu.%pa", &ioaddr);
+	if (ret)
+		goto out_list_del;
+
+	ret = iommu_device_register(&data->iommu, &mtk_iommu_ops, dev);
+	if (ret)
+		goto out_sysfs_remove;
+
 	if (MTK_IOMMU_IS_TYPE(data->plat_data, MTK_IOMMU_TYPE_MM)) {
 		ret = component_master_add_with_match(dev, &mtk_iommu_com_ops, match);
 		if (ret)
-			goto out_list_del;
+			goto out_device_unregister;
 	}
 	return ret;
 
-out_list_del:
-	list_del(&data->list);
+out_device_unregister:
 	iommu_device_unregister(&data->iommu);
 out_sysfs_remove:
 	iommu_device_sysfs_remove(&data->iommu);
-out_link_remove:
+out_list_del:
+	list_del(&data->list);
 	if (MTK_IOMMU_IS_TYPE(data->plat_data, MTK_IOMMU_TYPE_MM))
 		device_link_remove(data->smicomm_dev, dev);
 out_runtime_disable: