Commit 1ca55d50 authored by Oleksandr Tyshchenko's avatar Oleksandr Tyshchenko Committed by Juergen Gross
Browse files

xen/grant-dma-iommu: Introduce stub IOMMU driver 



In order to reuse generic IOMMU device tree bindings by Xen grant
DMA-mapping layer we need to add this stub driver from a fw_devlink
perspective (grant-dma-ops cannot be converted into the proper
IOMMU driver).

Otherwise, just reusing IOMMU bindings (without having a corresponding
driver) leads to the deferred probe timeout afterwards, because
the IOMMU device never becomes available.

This stub driver does nothing except registering empty iommu_ops,
the upper layer "of_iommu" will treat this as NO_IOMMU condition
and won't return -EPROBE_DEFER.

As this driver is quite different from the most hardware IOMMU
implementations and only needed in Xen guests, place it in drivers/xen
directory. The subsequent commit will make use of it.

Signed-off-by: default avatarOleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Reviewed-by: default avatarStefano Stabellini <sstabellini@kernel.org>
Link: https://lore.kernel.org/r/1654197833-25362-7-git-send-email-olekstysh@gmail.com


Signed-off-by: default avatarJuergen Gross <jgross@suse.com>
parent add413a1

drivers/xen/Kconfig

+4 −0
Original line number Diff line number Diff line
@@ -335,6 +335,10 @@ config XEN_UNPOPULATED_ALLOC 
	  having to balloon out RAM regions in order to obtain physical memory

	  space to create such mappings.



config XEN_GRANT_DMA_IOMMU

	bool

	select IOMMU_API



config XEN_GRANT_DMA_OPS

	bool

	select DMA_OPS

drivers/xen/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -40,3 +40,4 @@ xen-privcmd-y := privcmd.o privcmd-buf.o 
obj-$(CONFIG_XEN_FRONT_PGDIR_SHBUF)	+= xen-front-pgdir-shbuf.o

obj-$(CONFIG_XEN_UNPOPULATED_ALLOC)	+= unpopulated-alloc.o

obj-$(CONFIG_XEN_GRANT_DMA_OPS)		+= grant-dma-ops.o

obj-$(CONFIG_XEN_GRANT_DMA_IOMMU)	+= grant-dma-iommu.o

drivers/xen/grant-dma-iommu.c

0 → 100644
+78 −0
Original line number Diff line number Diff line 
// 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;

};



/* Nothing is really needed here */

static const struct iommu_ops grant_dma_iommu_ops;



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 int 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);



	return 0;

}



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);