| Message ID | 20200629130359.2690853-2-hch@lst.de |
|---|---|
| State | New |
| Headers | show |
| Series | [1/4] dma-mapping: add a new dma_need_sync API | expand |
On Mon, Jun 29, 2020 at 03:03:56PM +0200, Christoph Hellwig wrote: > Add a new API to check if calls to dma_sync_single_for_{device,cpu} are > required for a given DMA streaming mapping. > > +:: > + > + bool > + dma_need_sync(struct device *dev, dma_addr_t dma_addr); > + > +Returns %true if dma_sync_single_for_{device,cpu} calls are required to > +transfer memory ownership. Returns %false if those calls can be skipped. Hi Christoph - Thie call above is for a specific dma_addr. For correctness, would I need to check every addr, or can I assume that for a specific memory type (pages returned from malloc), that the answer would be identical? -- Jonathan
On Mon, Jul 06, 2020 at 12:42:27PM -0700, Jonathan Lemon wrote: > On Mon, Jun 29, 2020 at 03:03:56PM +0200, Christoph Hellwig wrote: > > Add a new API to check if calls to dma_sync_single_for_{device,cpu} are > > required for a given DMA streaming mapping. > > > > +:: > > + > > + bool > > + dma_need_sync(struct device *dev, dma_addr_t dma_addr); > > + > > +Returns %true if dma_sync_single_for_{device,cpu} calls are required to > > +transfer memory ownership. Returns %false if those calls can be skipped. > > Hi Christoph - > > Thie call above is for a specific dma_addr. For correctness, would I > need to check every addr, or can I assume that for a specific memory > type (pages returned from malloc), that the answer would be identical? You need to check every mapping. E.g. this API pairs with a dma_map_single/page call. For S/G mappings you'd need to call it for each entry, although if you have a use case for that we really should add a dma_sg_need_sync helper instea of open coding the scatterlist walk.
On Tue, Jul 07, 2020 at 08:47:30AM +0200, Christoph Hellwig wrote: > On Mon, Jul 06, 2020 at 12:42:27PM -0700, Jonathan Lemon wrote: > > On Mon, Jun 29, 2020 at 03:03:56PM +0200, Christoph Hellwig wrote: > > > Add a new API to check if calls to dma_sync_single_for_{device,cpu} are > > > required for a given DMA streaming mapping. > > > > > > +:: > > > + > > > + bool > > > + dma_need_sync(struct device *dev, dma_addr_t dma_addr); > > > + > > > +Returns %true if dma_sync_single_for_{device,cpu} calls are required to > > > +transfer memory ownership. Returns %false if those calls can be skipped. > > > > Hi Christoph - > > > > Thie call above is for a specific dma_addr. For correctness, would I > > need to check every addr, or can I assume that for a specific memory > > type (pages returned from malloc), that the answer would be identical? > > You need to check every mapping. E.g. this API pairs with a > dma_map_single/page call. For S/G mappings you'd need to call it for > each entry, although if you have a use case for that we really should > add a dma_sg_need_sync helper instea of open coding the scatterlist walk. My use case is setting up a pinned memory area, and caching the dma mappings. I'd like to bypass storing the DMA addresses if they aren't needed. For example: setup() { if (dma_need_sync(dev, addr, len)) { kvmalloc_array(...) cache_dma_mappings(...) } dev_get_dma(page) { if (!cache) return page_to_phys(page) return dma_cache_lookup(...) The reason for doing it this way is that the page in question may be backed by either system memory, or device memory such as a GPU. For the latter, the GPU provides a table of DMA addresses where data may be accessed, so I'm unable to use the dma_map_page() API. -- Jonathan
On Tue, Jul 07, 2020 at 08:11:09AM -0700, Jonathan Lemon wrote: > > You need to check every mapping. E.g. this API pairs with a > > dma_map_single/page call. For S/G mappings you'd need to call it for > > each entry, although if you have a use case for that we really should > > add a dma_sg_need_sync helper instea of open coding the scatterlist walk. > > My use case is setting up a pinned memory area, and caching the dma > mappings. I'd like to bypass storing the DMA addresses if they aren't > needed. For example: > > setup() > { > if (dma_need_sync(dev, addr, len)) { > kvmalloc_array(...) > cache_dma_mappings(...) > } > > > dev_get_dma(page) > { > if (!cache) > return page_to_phys(page) > > return dma_cache_lookup(...) > > > > The reason for doing it this way is that the page in question may be > backed by either system memory, or device memory such as a GPU. For the > latter, the GPU provides a table of DMA addresses where data may be > accessed, so I'm unable to use the dma_map_page() API. dma_need_sync doesn't tell you if the unmap needs the dma_addr_t. I've been think about replacing CONFIG_NEED_DMA_MAP_STATE with a runtime for a while, which would give you exattly what you need. For now it isn't very useful as there are very few configs left that do not have CONFIG_NEED_DMA_MAP_STATE set.
diff --git a/Documentation/core-api/dma-api.rst b/Documentation/core-api/dma-api.rst index 2d8d2fed731720..f41620439ef349 100644 --- a/Documentation/core-api/dma-api.rst +++ b/Documentation/core-api/dma-api.rst @@ -204,6 +204,14 @@ Returns the maximum size of a mapping for the device. The size parameter of the mapping functions like dma_map_single(), dma_map_page() and others should not be larger than the returned value. +:: + + bool + dma_need_sync(struct device *dev, dma_addr_t dma_addr); + +Returns %true if dma_sync_single_for_{device,cpu} calls are required to +transfer memory ownership. Returns %false if those calls can be skipped. + :: unsigned long diff --git a/include/linux/dma-direct.h b/include/linux/dma-direct.h index cdfa400f89b3d3..5184735a0fe8eb 100644 --- a/include/linux/dma-direct.h +++ b/include/linux/dma-direct.h @@ -85,4 +85,5 @@ int dma_direct_mmap(struct device *dev, struct vm_area_struct *vma, void *cpu_addr, dma_addr_t dma_addr, size_t size, unsigned long attrs); int dma_direct_supported(struct device *dev, u64 mask); +bool dma_direct_need_sync(struct device *dev, dma_addr_t dma_addr); #endif /* _LINUX_DMA_DIRECT_H */ diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h index 78f677cf45ab69..a33ed3954ed465 100644 --- a/include/linux/dma-mapping.h +++ b/include/linux/dma-mapping.h @@ -461,6 +461,7 @@ int dma_set_mask(struct device *dev, u64 mask); int dma_set_coherent_mask(struct device *dev, u64 mask); u64 dma_get_required_mask(struct device *dev); size_t dma_max_mapping_size(struct device *dev); +bool dma_need_sync(struct device *dev, dma_addr_t dma_addr); unsigned long dma_get_merge_boundary(struct device *dev); #else /* CONFIG_HAS_DMA */ static inline dma_addr_t dma_map_page_attrs(struct device *dev, @@ -571,6 +572,10 @@ static inline size_t dma_max_mapping_size(struct device *dev) { return 0; } +static inline bool dma_need_sync(struct device *dev, dma_addr_t dma_addr) +{ + return false; +} static inline unsigned long dma_get_merge_boundary(struct device *dev) { return 0; diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c index 93f578a8e613ba..95866b64758100 100644 --- a/kernel/dma/direct.c +++ b/kernel/dma/direct.c @@ -539,3 +539,9 @@ size_t dma_direct_max_mapping_size(struct device *dev) return swiotlb_max_mapping_size(dev); return SIZE_MAX; } + +bool dma_direct_need_sync(struct device *dev, dma_addr_t dma_addr) +{ + return !dev_is_dma_coherent(dev) || + is_swiotlb_buffer(dma_to_phys(dev, dma_addr)); +} diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c index 98e3d873792ea4..a8c18c9a796fdc 100644 --- a/kernel/dma/mapping.c +++ b/kernel/dma/mapping.c @@ -397,6 +397,16 @@ size_t dma_max_mapping_size(struct device *dev) } EXPORT_SYMBOL_GPL(dma_max_mapping_size); +bool dma_need_sync(struct device *dev, dma_addr_t dma_addr) +{ + const struct dma_map_ops *ops = get_dma_ops(dev); + + if (dma_is_direct(ops)) + return dma_direct_need_sync(dev, dma_addr); + return ops->sync_single_for_cpu || ops->sync_single_for_device; +} +EXPORT_SYMBOL_GPL(dma_need_sync); + unsigned long dma_get_merge_boundary(struct device *dev) { const struct dma_map_ops *ops = get_dma_ops(dev);
Add a new API to check if calls to dma_sync_single_for_{device,cpu} are required for a given DMA streaming mapping. Signed-off-by: Christoph Hellwig <hch@lst.de> --- Documentation/core-api/dma-api.rst | 8 ++++++++ include/linux/dma-direct.h | 1 + include/linux/dma-mapping.h | 5 +++++ kernel/dma/direct.c | 6 ++++++ kernel/dma/mapping.c | 10 ++++++++++ 5 files changed, 30 insertions(+)