// SPDX-License-Identifier: GPL-2.0
/*
 * Stub IOMMU driver which does nothing.
 * The main purpose of it being present is to reuse generic IOMMU device tree
 * bindings by Xen grant DMA-mapping layer.
 *
 * Copyright (C) 2022 EPAM Systems Inc.
 */

#include <linux/iommu.h>
#include <linux/of.h>
#include <linux/platform_device.h>

struct grant_dma_iommu_device {
        struct device *dev;
        struct iommu_device iommu;
};

static struct iommu_device *grant_dma_iommu_probe_device(struct device *dev)
{
        return ERR_PTR(-ENODEV);
}

/* Nothing is really needed here except a dummy probe_device callback */
static const struct iommu_ops grant_dma_iommu_ops = {
        .probe_device = grant_dma_iommu_probe_device,
};

static const struct of_device_id grant_dma_iommu_of_match[] = {
        { .compatible = "xen,grant-dma" },
        { },
};

static int grant_dma_iommu_probe(struct platform_device *pdev)
{
        struct grant_dma_iommu_device *mmu;
        int ret;

        mmu = devm_kzalloc(&pdev->dev, sizeof(*mmu), GFP_KERNEL);
        if (!mmu)
                return -ENOMEM;

        mmu->dev = &pdev->dev;

        ret = iommu_device_register(&mmu->iommu, &grant_dma_iommu_ops, &pdev->dev);
        if (ret)
                return ret;

        platform_set_drvdata(pdev, mmu);

        return 0;
}

static void grant_dma_iommu_remove(struct platform_device *pdev)
{
        struct grant_dma_iommu_device *mmu = platform_get_drvdata(pdev);

        platform_set_drvdata(pdev, NULL);
        iommu_device_unregister(&mmu->iommu);
}

static struct platform_driver grant_dma_iommu_driver = {
        .driver = {
                .name = "grant-dma-iommu",
                .of_match_table = grant_dma_iommu_of_match,
        },
        .probe = grant_dma_iommu_probe,
        .remove = grant_dma_iommu_remove,
};

static int __init grant_dma_iommu_init(void)
{
        struct device_node *iommu_np;

        iommu_np = of_find_matching_node(NULL, grant_dma_iommu_of_match);
        if (!iommu_np)
                return 0;

        of_node_put(iommu_np);

        return platform_driver_register(&grant_dma_iommu_driver);
}
subsys_initcall(grant_dma_iommu_init);