[RFC PATCH] iommu/dma: Allow drivers to reserve an iova range

[Isaac J. Manjarres]

From: Liam Mark <lmark@xxxxxxxxxxxxxx>

Some devices have a memory map which contains gaps or holes.
In order for the device to have as much IOVA space as possible,
allow its driver to inform the DMA-IOMMU layer that it should
not allocate addresses from these holes.

Change-Id: I15bd1d313d889c2572d0eb2adecf6bebde3267f7
Signed-off-by: Isaac J. Manjarres <isaacm@xxxxxxxxxxxxxx>
---
 drivers/iommu/dma-iommu.c | 28 ++++++++++++++++++++++++++++
 include/linux/dma-iommu.h |  9 +++++++++
 2 files changed, 37 insertions(+)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index a2e96a5..3b83e1a 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -368,6 +368,34 @@ static int iommu_dma_deferred_attach(struct device *dev,
 	return 0;
 }
 
+/*
+ * Should be called prior to using dma-apis
+ */
+int iommu_dma_reserve_iova(struct device *dev, dma_addr_t base,
+			   u64 size)
+{
+	struct iommu_domain *domain;
+	struct iommu_dma_cookie *cookie;
+	struct iova_domain *iovad;
+	unsigned long pfn_lo, pfn_hi;
+
+	domain = iommu_get_domain_for_dev(dev);
+	if (!domain || !domain->iova_cookie)
+		return -EINVAL;
+
+	cookie = domain->iova_cookie;
+	iovad = &cookie->iovad;
+
+	/* iova will be freed automatically by put_iova_domain() */
+	pfn_lo = iova_pfn(iovad, base);
+	pfn_hi = iova_pfn(iovad, base + size - 1);
+	if (!reserve_iova(iovad, pfn_lo, pfn_hi))
+		return -EINVAL;
+
+	return 0;
+}
+EXPORT_SYMBOL(iommu_dma_reserve_iova);
+
 /**
  * dma_info_to_prot - Translate DMA API directions and attributes to IOMMU API
  *                    page flags.
diff --git a/include/linux/dma-iommu.h b/include/linux/dma-iommu.h
index 2112f21..79eef7c 100644
--- a/include/linux/dma-iommu.h
+++ b/include/linux/dma-iommu.h
@@ -37,6 +37,9 @@ void iommu_dma_compose_msi_msg(struct msi_desc *desc,
 
 void iommu_dma_get_resv_regions(struct device *dev, struct list_head *list);
 
+int iommu_dma_reserve_iova(struct device *dev, dma_addr_t base,
+			   u64 size);
+
 #else /* CONFIG_IOMMU_DMA */
 
 struct iommu_domain;
@@ -78,5 +81,11 @@ static inline void iommu_dma_get_resv_regions(struct device *dev, struct list_he
 {
 }
 
+static inline int iommu_dma_reserve_iova(struct device *dev, dma_addr_t base,
+					 u64 size)
+{
+	return -ENODEV;
+}
+
 #endif	/* CONFIG_IOMMU_DMA */
 #endif	/* __DMA_IOMMU_H */
-- 
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