From: Oleksandr Tyshchenko <[email protected]>
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 <[email protected]>
---
According to the discussion at:
https://lore.kernel.org/xen-devel/[email protected]/
Change V2 -> V3:
- new patch
---
drivers/xen/Kconfig | 4 +++
drivers/xen/Makefile | 1 +
drivers/xen/grant-dma-iommu.c | 78 +++++++++++++++++++++++++++++++++++++++++++
3 files changed, 83 insertions(+)
create mode 100644 drivers/xen/grant-dma-iommu.c
diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
index a7bd8ce..35d20d9 100644
--- a/drivers/xen/Kconfig
+++ b/drivers/xen/Kconfig
@@ -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
diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
index 1a23cb0..c0503f1 100644
--- a/drivers/xen/Makefile
+++ b/drivers/xen/Makefile
@@ -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
diff --git a/drivers/xen/grant-dma-iommu.c b/drivers/xen/grant-dma-iommu.c
new file mode 100644
index 00000000..16b8bc0
--- /dev/null
+++ b/drivers/xen/grant-dma-iommu.c
@@ -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);
--
2.7.4
On Tue, 31 May 2022, Oleksandr Tyshchenko wrote:
> From: Oleksandr Tyshchenko <[email protected]>
>
> 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 <[email protected]>
Reviewed-by: Stefano Stabellini <[email protected]>
> ---
> According to the discussion at:
> https://lore.kernel.org/xen-devel/[email protected]/
>
> Change V2 -> V3:
> - new patch
> ---
> drivers/xen/Kconfig | 4 +++
> drivers/xen/Makefile | 1 +
> drivers/xen/grant-dma-iommu.c | 78 +++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 83 insertions(+)
> create mode 100644 drivers/xen/grant-dma-iommu.c
>
> diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
> index a7bd8ce..35d20d9 100644
> --- a/drivers/xen/Kconfig
> +++ b/drivers/xen/Kconfig
> @@ -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
> diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
> index 1a23cb0..c0503f1 100644
> --- a/drivers/xen/Makefile
> +++ b/drivers/xen/Makefile
> @@ -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
> diff --git a/drivers/xen/grant-dma-iommu.c b/drivers/xen/grant-dma-iommu.c
> new file mode 100644
> index 00000000..16b8bc0
> --- /dev/null
> +++ b/drivers/xen/grant-dma-iommu.c
> @@ -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);
> --
> 2.7.4
>
>
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