[PATCH v3 2/2] iommu: apple-dart: Support specifying the DMA aperture in the DT
Janne Grunau
j at jannau.net
Wed Sep 2 12:18:55 PDT 2026
Apple DARTs are often connected directly to devices that expect only a
portion of their address space to be used for DMA (for example, because
other ranges are mapped directly to something else). Devices can specify
the start and end of the aperture via "iommus" args if the DART device
node specifies "#iommu-cells = <5>. Aperture start and length are 64-bit
values as apertures above and larger than 4GB are used.
Limit compile testing to 64-bit architectures to avoid warnings in the
calculation of 64-bit dma_addr_t values.
This range *can* be outside of the DART's IAS. In that case, it is
assumed that the hardware truncates addresses and the page tables will
only map the lower bits of the address. However, the specified range
cannot straddle an IAS boundary (you cannot cover more than IAS worth
of address space nor wrap).
This corresponds to the vm-base and vm-size properties on the Apple
device tree side of things.
Co-developed-by: Hector Martin <marcan at marcan.st>
Signed-off-by: Hector Martin <marcan at marcan.st>
Reviewed-by: Sven Peter <sven at kernel.org>
Signed-off-by: Janne Grunau <j at jannau.net>
---
drivers/iommu/Kconfig | 2 +-
drivers/iommu/apple-dart.c | 74 ++++++++++++++++++++++++++++++++++++++++------
2 files changed, 66 insertions(+), 10 deletions(-)
diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
index 6e07bd69467a..27954f462582 100644
--- a/drivers/iommu/Kconfig
+++ b/drivers/iommu/Kconfig
@@ -303,7 +303,7 @@ config SPAPR_TCE_IOMMU
config APPLE_DART
tristate "Apple DART IOMMU Support"
- depends on ARCH_APPLE || COMPILE_TEST
+ depends on ARCH_APPLE || (COMPILE_TEST && 64BIT)
depends on !GENERIC_ATOMIC64 # for IOMMU_IO_PGTABLE_DART
select IOMMU_API
select IOMMU_IO_PGTABLE_DART
diff --git a/drivers/iommu/apple-dart.c b/drivers/iommu/apple-dart.c
index b160fb464c5f..ebf4547d32b4 100644
--- a/drivers/iommu/apple-dart.c
+++ b/drivers/iommu/apple-dart.c
@@ -21,6 +21,7 @@
#include <linux/io-pgtable.h>
#include <linux/iommu.h>
#include <linux/iopoll.h>
+#include <linux/minmax.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/of_address.h>
@@ -267,6 +268,7 @@ struct apple_dart_domain {
struct io_pgtable_ops *pgtbl_ops;
bool finalized;
+ u64 mask;
struct mutex init_lock;
struct apple_dart_atomic_stream_map stream_maps[MAX_DARTS_PER_DEVICE];
@@ -285,6 +287,13 @@ struct apple_dart_master_cfg {
/* Intersection of DART capabilitles */
u32 supports_bypass : 1;
+ /*
+ * DMA aperture start and end to be overridden by "iommus"' phandle
+ * args. By default determined by DART's ias but may be outside of it.
+ */
+ dma_addr_t dma_min;
+ dma_addr_t dma_max;
+
struct apple_dart_stream_map stream_maps[MAX_DARTS_PER_DEVICE];
};
@@ -537,7 +546,7 @@ static phys_addr_t apple_dart_iova_to_phys(struct iommu_domain *domain,
if (!ops)
return 0;
- return ops->iova_to_phys(ops, iova);
+ return ops->iova_to_phys(ops, iova & dart_domain->mask);
}
static int apple_dart_map_pages(struct iommu_domain *domain, unsigned long iova,
@@ -551,8 +560,8 @@ static int apple_dart_map_pages(struct iommu_domain *domain, unsigned long iova,
if (!ops)
return -ENODEV;
- return ops->map_pages(ops, iova, paddr, pgsize, pgcount, prot, gfp,
- mapped);
+ return ops->map_pages(ops, iova & dart_domain->mask, paddr, pgsize,
+ pgcount, prot, gfp, mapped);
}
static size_t apple_dart_unmap_pages(struct iommu_domain *domain,
@@ -563,7 +572,8 @@ static size_t apple_dart_unmap_pages(struct iommu_domain *domain,
struct apple_dart_domain *dart_domain = to_dart_domain(domain);
struct io_pgtable_ops *ops = dart_domain->pgtbl_ops;
- return ops->unmap_pages(ops, iova, pgsize, pgcount, gather);
+ return ops->unmap_pages(ops, iova & dart_domain->mask, pgsize, pgcount,
+ gather);
}
static void
@@ -590,6 +600,7 @@ static int apple_dart_finalize_domain(struct apple_dart_domain *dart_domain,
{
struct apple_dart *dart = cfg->stream_maps[0].dart;
struct io_pgtable_cfg pgtbl_cfg;
+ u32 ias = min_t(u32, dart->ias, fls64(cfg->dma_max));
int ret = 0;
int i, j;
@@ -610,7 +621,7 @@ static int apple_dart_finalize_domain(struct apple_dart_domain *dart_domain,
pgtbl_cfg = (struct io_pgtable_cfg){
.pgsize_bitmap = dart->pgsize,
- .ias = dart->ias,
+ .ias = ias,
.oas = dart->oas,
.coherent_walk = 1,
.iommu_dev = dart->dev,
@@ -623,10 +634,10 @@ static int apple_dart_finalize_domain(struct apple_dart_domain *dart_domain,
goto done;
}
+ dart_domain->mask = DMA_BIT_MASK(pgtbl_cfg.ias);
dart_domain->domain.pgsize_bitmap = pgtbl_cfg.pgsize_bitmap;
- dart_domain->domain.geometry.aperture_start = 0;
- dart_domain->domain.geometry.aperture_end =
- (dma_addr_t)DMA_BIT_MASK(pgtbl_cfg.ias);
+ dart_domain->domain.geometry.aperture_start = cfg->dma_min;
+ dart_domain->domain.geometry.aperture_end = cfg->dma_max;
dart_domain->domain.geometry.force_aperture = true;
dart_domain->finalized = true;
@@ -803,20 +814,65 @@ static int apple_dart_of_xlate(struct device *dev,
struct platform_device *iommu_pdev = of_find_device_by_node(args->np);
struct apple_dart *dart = platform_get_drvdata(iommu_pdev);
struct apple_dart *cfg_dart;
+ dma_addr_t dma_max = DMA_BIT_MASK(dart->ias);
+ dma_addr_t dma_min = 0;
int i, sid;
put_device(&iommu_pdev->dev);
- if (args->args_count != 1)
+ if (args->args_count != 1 && args->args_count != 5)
return -EINVAL;
+
sid = args->args[0];
+ if (args->args_count == 5) {
+ dma_addr_t length = ((dma_addr_t)args->args[3] << 32) | args->args[4];
+
+ if (!length)
+ return -EINVAL;
+
+ dma_min = ((dma_addr_t)args->args[1] << 32) | args->args[2];
+
+ if (!IS_ALIGNED(dma_min, dart->pgsize) ||
+ !IS_ALIGNED(length, dart->pgsize)) {
+ dev_err(dev, "Unaligned DMA window %pad, %pad (0x%x)\n",
+ &dma_min, &length, dart->pgsize);
+ return -EINVAL;
+ }
+ if (check_add_overflow(dma_min, length - 1, &dma_max)) {
+ dev_err(dev, "DMA window length (%pad) overflows range for start %pad\n",
+ &length, &dma_min);
+ return -EINVAL;
+ }
+
+ /*
+ * Ensure that the DMA window does not exceed the DART's ias.
+ */
+ if ((dma_min ^ dma_max) & ~DMA_BIT_MASK(dart->ias)) {
+ dev_err(dev, "Invalid DMA window for ias=%d\n",
+ dart->ias);
+ return -EINVAL;
+ }
+ }
+
if (!cfg) {
cfg = kzalloc_obj(*cfg);
if (!cfg)
return -ENOMEM;
/* Will be ANDed with DART capabilities */
cfg->supports_bypass = true;
+ /* Will be merged with other DARTs to the common range. */
+ cfg->dma_min = dma_min;
+ cfg->dma_max = dma_max;
+ } else {
+ if (dma_min >= cfg->dma_max || cfg->dma_min >= dma_max) {
+ dev_err(dev, "non-overlapping DMA windows: %pad..%pad, %pad..%pad\n",
+ &dma_min, &dma_max,
+ &cfg->dma_min, &cfg->dma_max);
+ return -EINVAL;
+ }
+ cfg->dma_min = max(dma_min, cfg->dma_min);
+ cfg->dma_max = min(dma_max, cfg->dma_max);
}
dev_iommu_priv_set(dev, cfg);
--
2.55.0
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