[PATCH 2/4] iommu/io-pgtable: Add DART subpage protection support

[Sven Peter]

DART allows to only expose a subpage to the device. While this is an
optional feature on the M1 DARTs the new ones present on the Pro/Max
models require this field in every PTE.

Signed-off-by: Sven Peter <sven at svenpeter.dev>
---
 drivers/iommu/io-pgtable-arm.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
index dd9e47189d0d..a8c660b8b3e9 100644
--- a/drivers/iommu/io-pgtable-arm.c
+++ b/drivers/iommu/io-pgtable-arm.c
@@ -10,6 +10,7 @@
 #define pr_fmt(fmt)	"arm-lpae io-pgtable: " fmt
 
 #include <linux/atomic.h>
+#include <linux/bitfield.h>
 #include <linux/bitops.h>
 #include <linux/io-pgtable.h>
 #include <linux/kernel.h>
@@ -133,6 +134,9 @@
 #define APPLE_DART_PTE_PROT_NO_WRITE (1<<7)
 #define APPLE_DART_PTE_PROT_NO_READ (1<<8)
 
+#define APPLE_DART_PTE_SUBPAGE_START	GENMASK_ULL(63, 52)
+#define APPLE_DART_PTE_SUBPAGE_END	GENMASK_ULL(51, 40)
+
 /* IOPTE accessors */
 #define iopte_deref(pte,d) __va(iopte_to_paddr(pte, d))
 
@@ -273,6 +277,12 @@ static void __arm_lpae_init_pte(struct arm_lpae_io_pgtable *data,
 	else
 		pte |= ARM_LPAE_PTE_TYPE_BLOCK;
 
+	if (data->iop.fmt == APPLE_DART) {
+		/* subpage protection: always allow access to the entire page */
+		pte |= FIELD_PREP(APPLE_DART_PTE_SUBPAGE_START, 0);
+		pte |= FIELD_PREP(APPLE_DART_PTE_SUBPAGE_END, 0xfff);
+	}
+
 	for (i = 0; i < num_entries; i++)
 		ptep[i] = pte | paddr_to_iopte(paddr + i * sz, data);
 
-- 
2.25.1