Re: [PATCH v5 2/5] iommu: Implement of_iommu_get_resv_regions()

Janne Grunau
2022-05-15T11:10:49Z

On 2022-05-12 21:00:49 +0200, Thierry Reding wrote:
> From: Thierry Reding <treding@nvidia.com>
>
> This is an implementation that IOMMU drivers can use to obtain reserved
> memory regions from a device tree node. It uses the reserved-memory DT
> bindings to find the regions associated with a given device. If these
> regions are marked accordingly, identity mappings will be created for
> them in the IOMMU domain that the devices will be attached to.
>
> Signed-off-by: Thierry Reding <treding@nvidia.com>
> ---
> Changes in v5:
> - update for new "iommu-addresses" device tree bindings
>
> Changes in v4:
> - fix build failure on !CONFIG_OF_ADDRESS
>
> Changes in v3:
> - change "active" property to identity mapping flag that is part of the
> memory region specifier (as defined by #memory-region-cells) to allow
> per-reference flags to be used
>
> Changes in v2:
> - use "active" property to determine whether direct mappings are needed
>
> drivers/iommu/of_iommu.c | 90 ++++++++++++++++++++++++++++++++++++++++
> include/linux/of_iommu.h | 8 ++++
> 2 files changed, 98 insertions(+)
>
> diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
> index 5696314ae69e..9e341b5e307f 100644
> --- a/drivers/iommu/of_iommu.c
> +++ b/drivers/iommu/of_iommu.c
> @@ -11,12 +11,15 @@
> #include <linux/module.h>
> #include <linux/msi.h>
> #include <linux/of.h>
> +#include <linux/of_address.h>
> #include <linux/of_iommu.h>
> #include <linux/of_pci.h>
> #include <linux/pci.h>
> #include <linux/slab.h>
> #include <linux/fsl/mc.h>
>
> +#include <dt-bindings/reserved-memory.h>
> +
> #define NO_IOMMU 1
>
> static int of_iommu_xlate(struct device *dev,
> @@ -172,3 +175,90 @@ const struct iommu_ops *of_iommu_configure(struct device *dev,
>
> return ops;
> }
> +
> +/**
> + * of_iommu_get_resv_regions - reserved region driver helper for device tree
> + * @dev: device for which to get reserved regions
> + * @list: reserved region list
> + *
> + * IOMMU drivers can use this to implement their .get_resv_regions() callback
> + * for memory regions attached to a device tree node. See the reserved-memory
> + * device tree bindings on how to use these:
> + *
> + * Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
> + */
> +void of_iommu_get_resv_regions(struct device *dev, struct list_head *list)
> +{
> +#if IS_ENABLED(CONFIG_OF_ADDRESS)
> + struct of_phandle_iterator it;
> + int err;
> +
> + of_for_each_phandle(&it, err, dev->of_node, "memory-region", NULL, 0) {
> + struct iommu_resv_region *region;
> + struct resource res;
> + const __be32 *maps;
> + int size;

Adding 'if (!of_device_is_available(it.node)) continue;' here would help
backwards compatibility. My plan was to add the reserved regions with
"iommu-addresses" with all zero adresses and sizes with status =
"disabled" to the devicetree. A bootloader update is required to fill
those.

> +
> + memset(&res, 0, sizeof(res));
> +
> + /*
> + * The "reg" property is optional and can be omitted by reserved-memory regions
> + * that represent reservations in the IOVA space, which are regions that should
> + * not be mapped.
> + */
> + if (of_find_property(it.node, "reg", NULL)) {
> + err = of_address_to_resource(it.node, 0, &res);
> + if (err < 0) {
> + dev_err(dev, "failed to parse memory region %pOF: %d\n",
> + it.node, err);
> + continue;
> + }
> + }
> +
> + maps = of_get_property(it.node, "iommu-addresses", &size);
> + if (maps) {
> + const __be32 *end = maps + size / sizeof(__be32);
> + struct device_node *np;
> + unsigned int index = 0;
> + u32 phandle;
> + int na, ns;
> +
> + while (maps < end) {
> + phys_addr_t start, end;
> + size_t length;
> +
> + phandle = be32_to_cpup(maps++);
> + np = of_find_node_by_phandle(phandle);
> + na = of_n_addr_cells(np);
> + ns = of_n_size_cells(np);
> +
> + start = of_translate_dma_address(np, maps);
> + length = of_read_number(maps + na, ns);

alternatively we could handle mappings/reservations with length 0 as
error and skip them.

> + end = start + length - 1;
> +
> + if (np == dev->of_node) {
> + int prot = IOMMU_READ | IOMMU_WRITE;
> + enum iommu_resv_type type;
> +
> + /*
> + * IOMMU regions without an associated physical region
> + * cannot be mapped and are simply reservations.
> + */
> + if (res.end > res.start)
> + type = IOMMU_RESV_DIRECT_RELAXABLE;
> + else
> + type = IOMMU_RESV_RESERVED;
> +
> + region = iommu_alloc_resv_region(start, length, prot, type);
> + if (region)
> + list_add_tail(&region->list, list);
> + }
> +
> + maps += na + ns;
> + index++;
> + }
> + }
> + }
> +#endif
> +}
> +EXPORT_SYMBOL(of_iommu_get_resv_regions);
> diff --git a/include/linux/of_iommu.h b/include/linux/of_iommu.h
> index 55c1eb300a86..9a5e6b410dd2 100644
> --- a/include/linux/of_iommu.h
> +++ b/include/linux/of_iommu.h
> @@ -12,6 +12,9 @@ extern const struct iommu_ops *of_iommu_configure(struct device *dev,
> struct device_node *master_np,
> const u32 *id);
>
> +extern void of_iommu_get_resv_regions(struct device *dev,
> + struct list_head *list);
> +
> #else
>
> static inline const struct iommu_ops *of_iommu_configure(struct device *dev,
> @@ -21,6 +24,11 @@ static inline const struct iommu_ops *of_iommu_configure(struct device *dev,
> return NULL;
> }
>
> +static inline void of_iommu_get_resv_regions(struct device *dev,
> + struct list_head *list)
> +{
> +}
> +
> #endif /* CONFIG_OF_IOMMU */
>
> #endif /* __OF_IOMMU_H */
> --
> 2.36.1
>

Janne