From a229cc14f3395311b899e5e582b71efa8dd01df0 Mon Sep 17 00:00:00 2001 From: John Garry Date: Thu, 14 Jul 2022 19:15:24 +0800 Subject: dma-mapping: add dma_opt_mapping_size() Streaming DMA mapping involving an IOMMU may be much slower for larger total mapping size. This is because every IOMMU DMA mapping requires an IOVA to be allocated and freed. IOVA sizes above a certain limit are not cached, which can have a big impact on DMA mapping performance. Provide an API for device drivers to know this "optimal" limit, such that they may try to produce mapping which don't exceed it. Signed-off-by: John Garry Reviewed-by: Damien Le Moal Acked-by: Martin K. Petersen Signed-off-by: Christoph Hellwig --- kernel/dma/mapping.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) (limited to 'kernel/dma') diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c index db7244291b74..1bfe11b1edb6 100644 --- a/kernel/dma/mapping.c +++ b/kernel/dma/mapping.c @@ -773,6 +773,18 @@ size_t dma_max_mapping_size(struct device *dev) } EXPORT_SYMBOL_GPL(dma_max_mapping_size); +size_t dma_opt_mapping_size(struct device *dev) +{ + const struct dma_map_ops *ops = get_dma_ops(dev); + size_t size = SIZE_MAX; + + if (ops && ops->opt_mapping_size) + size = ops->opt_mapping_size(); + + return min(dma_max_mapping_size(dev), size); +} +EXPORT_SYMBOL_GPL(dma_opt_mapping_size); + bool dma_need_sync(struct device *dev, dma_addr_t dma_addr) { const struct dma_map_ops *ops = get_dma_ops(dev); -- cgit v1.2.3