From: Leon Romanovsky <[email protected]> The mapping buffers which carry this attribute require DMA coherent system. This means that they can't take SWIOTLB path, can perform CPU cache overlap and doesn't perform cache flushing.
Signed-off-by: Leon Romanovsky <[email protected]> --- Documentation/core-api/dma-attributes.rst | 16 ++++++++++++++++ include/linux/dma-mapping.h | 7 +++++++ include/trace/events/dma.h | 3 ++- kernel/dma/debug.c | 3 ++- kernel/dma/mapping.c | 6 ++++++ 5 files changed, 33 insertions(+), 2 deletions(-) diff --git a/Documentation/core-api/dma-attributes.rst b/Documentation/core-api/dma-attributes.rst index 48cfe86cc06d7..441bdc9d08318 100644 --- a/Documentation/core-api/dma-attributes.rst +++ b/Documentation/core-api/dma-attributes.rst @@ -163,3 +163,19 @@ data corruption. All mappings that share a cache line must set this attribute to suppress DMA debug warnings about overlapping mappings. + +DMA_ATTR_REQUIRE_COHERENT +------------------------- + +DMA mapping requests with the DMA_ATTR_REQUIRE_COHERENT fail on any +system where SWIOTLB or cache management is required. This should only +be used to support uAPI designs that require continuous HW DMA +coherence with userspace processes, for example RDMA and DRM. At a +minimum the memory being mapped must be userspace memory from +pin_user_pages() or similar. + +Drivers should consider using dma_mmap_pages() instead of this +interface when building their uAPIs, when possible. + +It must never be used in an in-kernel driver that only works with +kernal memory. diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h index da44394b3a1a7..482b919f040f7 100644 --- a/include/linux/dma-mapping.h +++ b/include/linux/dma-mapping.h @@ -86,6 +86,13 @@ */ #define DMA_ATTR_DEBUGGING_IGNORE_CACHELINES (1UL << 11) +/* + * DMA_ATTR_REQUIRE_COHERENT: Indicates that DMA coherency is required. + * All mappings that carry this attribute can't work with SWIOTLB and cache + * flushing. + */ +#define DMA_ATTR_REQUIRE_COHERENT (1UL << 12) + /* * A dma_addr_t can hold any valid DMA or bus address for the platform. It can * be given to a device to use as a DMA source or target. It is specific to a diff --git a/include/trace/events/dma.h b/include/trace/events/dma.h index 8c64bc0721fe4..63597b0044247 100644 --- a/include/trace/events/dma.h +++ b/include/trace/events/dma.h @@ -33,7 +33,8 @@ TRACE_DEFINE_ENUM(DMA_NONE); { DMA_ATTR_NO_WARN, "NO_WARN" }, \ { DMA_ATTR_PRIVILEGED, "PRIVILEGED" }, \ { DMA_ATTR_MMIO, "MMIO" }, \ - { DMA_ATTR_DEBUGGING_IGNORE_CACHELINES, "CACHELINES_OVERLAP" }) + { DMA_ATTR_DEBUGGING_IGNORE_CACHELINES, "CACHELINES_OVERLAP" }, \ + { DMA_ATTR_REQUIRE_COHERENT, "REQUIRE_COHERENT" }) DECLARE_EVENT_CLASS(dma_map, TP_PROTO(struct device *dev, phys_addr_t phys_addr, dma_addr_t dma_addr, diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c index 83e1cfe05f08d..0677918f06a80 100644 --- a/kernel/dma/debug.c +++ b/kernel/dma/debug.c @@ -601,7 +601,8 @@ static void add_dma_entry(struct dma_debug_entry *entry, unsigned long attrs) unsigned long flags; int rc; - entry->is_cache_clean = attrs & DMA_ATTR_DEBUGGING_IGNORE_CACHELINES; + entry->is_cache_clean = attrs & (DMA_ATTR_DEBUGGING_IGNORE_CACHELINES | + DMA_ATTR_REQUIRE_COHERENT); bucket = get_hash_bucket(entry, &flags); hash_bucket_add(bucket, entry); diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c index 3928a509c44c2..6d3dd0bd3a886 100644 --- a/kernel/dma/mapping.c +++ b/kernel/dma/mapping.c @@ -164,6 +164,9 @@ dma_addr_t dma_map_phys(struct device *dev, phys_addr_t phys, size_t size, if (WARN_ON_ONCE(!dev->dma_mask)) return DMA_MAPPING_ERROR; + if (!dev_is_dma_coherent(dev) && (attrs & DMA_ATTR_REQUIRE_COHERENT)) + return DMA_MAPPING_ERROR; + if (dma_map_direct(dev, ops) || (!is_mmio && arch_dma_map_phys_direct(dev, phys + size))) addr = dma_direct_map_phys(dev, phys, size, dir, attrs); @@ -235,6 +238,9 @@ static int __dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, BUG_ON(!valid_dma_direction(dir)); + if (!dev_is_dma_coherent(dev) && (attrs & DMA_ATTR_REQUIRE_COHERENT)) + return -EOPNOTSUPP; + if (WARN_ON_ONCE(!dev->dma_mask)) return 0; -- 2.53.0
