iommu/mediatek: Allow building as module

The IOMMU in many SoC depends on the MM clocks and power-domain which
are device_initcall normally, thus the subsys_init here is not helpful.
This patch switches it to module_platform_driver which also allow the
driver built as module.

Correspondingly switch the config to tristate, and update the
iommu_ops's owner.
Signed-off-by: NYong Wu <yong.wu@mediatek.com>
Link: https://lore.kernel.org/r/20210326032337.24578-2-yong.wu@mediatek.comSigned-off-by: NJoerg Roedel <jroedel@suse.de>

drivers/iommu/Kconfig

@@ -349,7 +349,7 @@ config S390_AP_IOMMU
 	  is not implemented as it is not necessary for VFIO.
 
 config MTK_IOMMU
-	bool "MTK IOMMU Support"
+	tristate "MediaTek IOMMU Support"
 	depends on ARCH_MEDIATEK || COMPILE_TEST
 	select ARM_DMA_USE_IOMMU
 	select IOMMU_API

drivers/iommu/mtk_iommu.c

@@ -17,6 +17,7 @@
 #include <linux/iopoll.h>
 #include <linux/list.h>
 #include <linux/mfd/syscon.h>
+#include <linux/module.h>
 #include <linux/of_address.h>
 #include <linux/of_iommu.h>
 #include <linux/of_irq.h>
@@ -683,6 +684,7 @@ static const struct iommu_ops mtk_iommu_ops = {
 	.get_resv_regions = mtk_iommu_get_resv_regions,
 	.put_resv_regions = generic_iommu_put_resv_regions,
 	.pgsize_bitmap	= SZ_4K | SZ_64K | SZ_1M | SZ_16M,
+	.owner		= THIS_MODULE,
 };
 
 static int mtk_iommu_hw_init(const struct mtk_iommu_data *data)
@@ -1079,16 +1081,7 @@ static struct platform_driver mtk_iommu_driver = {
 		.pm = &mtk_iommu_pm_ops,
 	}
 };
+module_platform_driver(mtk_iommu_driver);
 
-static int __init mtk_iommu_init(void)
-{
-	int ret;
-
-	ret = platform_driver_register(&mtk_iommu_driver);
-	if (ret != 0)
-		pr_err("Failed to register MTK IOMMU driver\n");
-
-	return ret;
-}
-
-subsys_initcall(mtk_iommu_init)
+MODULE_DESCRIPTION("IOMMU API for MediaTek M4U implementations");
+MODULE_LICENSE("GPL v2");