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

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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: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Link: https://lore.kernel.org/r/1654197833-25362-7-git-send-email-olekstysh@gmail.com
Signed-off-by: Juergen Gross <jgross@suse.com>
This commit is contained in:
Oleksandr Tyshchenko 2022-06-02 22:23:51 +03:00 committed by Juergen Gross
parent add413a1d9
commit 1ca55d50e5
3 changed files with 83 additions and 0 deletions
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4
drivers/xen/Kconfig
View File

@ -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

1
drivers/xen/Makefile
View File

@ -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

78
drivers/xen/grant-dma-iommu.c Normal file
View File

@ -0,0 +1,78 @@
// 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);