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Mon, 22 Dec 2025 18:36:58 -0800 (PST) From: Barry Song <21cnbao@gmail.com> To: 21cnbao@gmail.com, leon@kernel.org Cc: ada.coupriediaz@arm.com, anshuman.khandual@arm.com, ardb@kernel.org, catalin.marinas@arm.com, iommu@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, m.szyprowski@samsung.com, maz@kernel.org, robin.murphy@arm.com, ryan.roberts@arm.com, surenb@google.com, v-songbaohua@oppo.com, will@kernel.org, zhengtangquan@oppo.com Subject: Re: [PATCH 5/6] dma-mapping: Allow batched DMA sync operations if supported by the arch Date: Tue, 23 Dec 2025 15:36:46 +1300 Message-ID: <20251223023648.31614-1-21cnbao@gmail.com> X-Mailer: git-send-email 2.48.1 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit > > > > > I would also rename arch_sync_dma_batch_flush() to arch_sync_dma_flush(). > > Sure. > > > > > You can also minimize changes in dma_direct_map_phys() too, by extending > > it's signature to provide if flush is needed or not. > > Yes. I have > > static inline dma_addr_t __dma_direct_map_phys(struct device *dev, >                 phys_addr_t phys, size_t size, enum dma_data_direction dir, >                 unsigned long attrs, bool flush) > > and two wrappers: > static inline dma_addr_t dma_direct_map_phys(struct device *dev, >                 phys_addr_t phys, size_t size, enum dma_data_direction dir, >                 unsigned long attrs) > { >         return __dma_direct_map_phys(dev, phys, size, dir, attrs, true); > } > > static inline dma_addr_t dma_direct_map_phys_batch_add(struct device *dev, >                 phys_addr_t phys, size_t size, enum dma_data_direction dir, >                 unsigned long attrs) > { >         return __dma_direct_map_phys(dev, phys, size, dir, attrs, false); > } > > If you prefer exposing "flush" directly in dma_direct_map_phys() > and updating its callers with flush=true, I think that’s fine. > > It could be also true for dma_direct_sync_single_for_device(). sorry for typo. I meant dma_direct_sync_single_for_cpu(). With flush passed as an argument, the patch becomes the following. Please feel free to comment before I send v2. diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c index 50c3fe2a1d55..5c65d213eb37 100644 --- a/kernel/dma/direct.c +++ b/kernel/dma/direct.c @@ -403,9 +403,11 @@ void dma_direct_sync_sg_for_device(struct device *dev, swiotlb_sync_single_for_device(dev, paddr, sg->length, dir); if (!dev_is_dma_coherent(dev)) - arch_sync_dma_for_device(paddr, sg->length, + arch_sync_dma_for_device_batch_add(paddr, sg->length, dir); } + if (!dev_is_dma_coherent(dev)) + arch_sync_dma_flush(); } #endif @@ -422,7 +424,7 @@ void dma_direct_sync_sg_for_cpu(struct device *dev, phys_addr_t paddr = dma_to_phys(dev, sg_dma_address(sg)); if (!dev_is_dma_coherent(dev)) - arch_sync_dma_for_cpu(paddr, sg->length, dir); + arch_sync_dma_for_cpu_batch_add(paddr, sg->length, dir); swiotlb_sync_single_for_cpu(dev, paddr, sg->length, dir); @@ -430,8 +432,10 @@ void dma_direct_sync_sg_for_cpu(struct device *dev, arch_dma_mark_clean(paddr, sg->length); } - if (!dev_is_dma_coherent(dev)) + if (!dev_is_dma_coherent(dev)) { arch_sync_dma_for_cpu_all(); + arch_sync_dma_flush(); + } } /* @@ -443,14 +447,19 @@ void dma_direct_unmap_sg(struct device *dev, struct scatterlist *sgl, { struct scatterlist *sg; int i; + bool need_sync = false; for_each_sg(sgl, sg, nents, i) { - if (sg_dma_is_bus_address(sg)) + if (sg_dma_is_bus_address(sg)) { sg_dma_unmark_bus_address(sg); - else + } else { + need_sync = true; dma_direct_unmap_phys(dev, sg->dma_address, - sg_dma_len(sg), dir, attrs); + sg_dma_len(sg), dir, attrs, false); + } } + if (need_sync && !dev_is_dma_coherent(dev)) + arch_sync_dma_flush(); } #endif @@ -460,6 +469,7 @@ int dma_direct_map_sg(struct device *dev, struct scatterlist *sgl, int nents, struct pci_p2pdma_map_state p2pdma_state = {}; struct scatterlist *sg; int i, ret; + bool need_sync = false; for_each_sg(sgl, sg, nents, i) { switch (pci_p2pdma_state(&p2pdma_state, dev, sg_page(sg))) { @@ -471,8 +481,9 @@ int dma_direct_map_sg(struct device *dev, struct scatterlist *sgl, int nents, */ break; case PCI_P2PDMA_MAP_NONE: + need_sync = true; sg->dma_address = dma_direct_map_phys(dev, sg_phys(sg), - sg->length, dir, attrs); + sg->length, dir, attrs, false); if (sg->dma_address == DMA_MAPPING_ERROR) { ret = -EIO; goto out_unmap; @@ -491,6 +502,8 @@ int dma_direct_map_sg(struct device *dev, struct scatterlist *sgl, int nents, sg_dma_len(sg) = sg->length; } + if (need_sync && !dev_is_dma_coherent(dev)) + arch_sync_dma_flush(); return nents; out_unmap: diff --git a/kernel/dma/direct.h b/kernel/dma/direct.h index da2fadf45bcd..b13eb5bfd051 100644 --- a/kernel/dma/direct.h +++ b/kernel/dma/direct.h @@ -65,12 +65,15 @@ static inline void dma_direct_sync_single_for_device(struct device *dev, } static inline void dma_direct_sync_single_for_cpu(struct device *dev, - dma_addr_t addr, size_t size, enum dma_data_direction dir) + dma_addr_t addr, size_t size, enum dma_data_direction dir, + bool flush) { phys_addr_t paddr = dma_to_phys(dev, addr); if (!dev_is_dma_coherent(dev)) { - arch_sync_dma_for_cpu(paddr, size, dir); + arch_sync_dma_for_cpu_batch_add(paddr, size, dir); + if (flush) + arch_sync_dma_flush(); arch_sync_dma_for_cpu_all(); } @@ -82,7 +85,7 @@ static inline void dma_direct_sync_single_for_cpu(struct device *dev, static inline dma_addr_t dma_direct_map_phys(struct device *dev, phys_addr_t phys, size_t size, enum dma_data_direction dir, - unsigned long attrs) + unsigned long attrs, bool flush) { dma_addr_t dma_addr; @@ -109,8 +112,11 @@ static inline dma_addr_t dma_direct_map_phys(struct device *dev, } if (!dev_is_dma_coherent(dev) && - !(attrs & (DMA_ATTR_SKIP_CPU_SYNC | DMA_ATTR_MMIO))) - arch_sync_dma_for_device(phys, size, dir); + !(attrs & (DMA_ATTR_SKIP_CPU_SYNC | DMA_ATTR_MMIO))) { + arch_sync_dma_for_device_batch_add(phys, size, dir); + if (flush) + arch_sync_dma_flush(); + } return dma_addr; err_overflow: @@ -122,7 +128,8 @@ static inline dma_addr_t dma_direct_map_phys(struct device *dev, } static inline void dma_direct_unmap_phys(struct device *dev, dma_addr_t addr, - size_t size, enum dma_data_direction dir, unsigned long attrs) + size_t size, enum dma_data_direction dir, unsigned long attrs, + bool flush) { phys_addr_t phys; @@ -132,9 +139,10 @@ static inline void dma_direct_unmap_phys(struct device *dev, dma_addr_t addr, phys = dma_to_phys(dev, addr); if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC)) - dma_direct_sync_single_for_cpu(dev, addr, size, dir); + dma_direct_sync_single_for_cpu(dev, addr, size, dir, flush); swiotlb_tbl_unmap_single(dev, phys, size, dir, attrs | DMA_ATTR_SKIP_CPU_SYNC); } + #endif /* _KERNEL_DMA_DIRECT_H */ diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c index 37163eb49f9f..d8cfa56a3cbb 100644 --- a/kernel/dma/mapping.c +++ b/kernel/dma/mapping.c @@ -166,7 +166,7 @@ dma_addr_t dma_map_phys(struct device *dev, phys_addr_t phys, size_t size, 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); + addr = dma_direct_map_phys(dev, phys, size, dir, attrs, true); else if (use_dma_iommu(dev)) addr = iommu_dma_map_phys(dev, phys, size, dir, attrs); else if (ops->map_phys) @@ -207,7 +207,7 @@ void dma_unmap_phys(struct device *dev, dma_addr_t addr, size_t size, BUG_ON(!valid_dma_direction(dir)); if (dma_map_direct(dev, ops) || (!is_mmio && arch_dma_unmap_phys_direct(dev, addr + size))) - dma_direct_unmap_phys(dev, addr, size, dir, attrs); + dma_direct_unmap_phys(dev, addr, size, dir, attrs, true); else if (use_dma_iommu(dev)) iommu_dma_unmap_phys(dev, addr, size, dir, attrs); else if (ops->unmap_phys) @@ -373,7 +373,7 @@ void __dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr, size_t size, BUG_ON(!valid_dma_direction(dir)); if (dma_map_direct(dev, ops)) - dma_direct_sync_single_for_cpu(dev, addr, size, dir); + dma_direct_sync_single_for_cpu(dev, addr, size, dir, true); else if (use_dma_iommu(dev)) iommu_dma_sync_single_for_cpu(dev, addr, size, dir); else if (ops->sync_single_for_cpu) -- 2.43.0