provide in-place uncached remapping for dma-direct v2

provide in-place uncached remapping for dma-direct v2

[Christoph Hellwig]

Hi all,

this series provides support for remapping places uncached in-place in
the generic dma-direct code, and moves openrisc over from its own
in-place remapping scheme.  The arm64 folks also had interest in such
a scheme to avoid problems with speculating into cache aliases.

Also all architectures that always use small page mappings for the
kernel and have non-coherent DMA should look into enabling this
scheme, as it is much more efficient than the vmap remapping.

Changes since v1:
 - share the arch hook for inline remap and uncached segment support
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[PATCH 1/5] dma-direct: remove the cached_kernel_address hook

[Christoph Hellwig]

dma-direct now finds the kernel address for coherent allocations based
on the dma address, so the cached_kernel_address hooks is unused and
can be removed entirely.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 arch/Kconfig                    |  2 +-
 arch/microblaze/mm/consistent.c |  7 -------
 arch/mips/mm/dma-noncoherent.c  |  5 -----
 arch/nios2/mm/dma-mapping.c     | 10 ----------
 arch/xtensa/kernel/pci-dma.c    | 10 ++--------
 include/linux/dma-noncoherent.h |  1 -
 6 files changed, 3 insertions(+), 32 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 98de654b79b3..7994b239f155 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -249,7 +249,7 @@ config ARCH_HAS_SET_DIRECT_MAP
 
 #
 # Select if arch has an uncached kernel segment and provides the
-# uncached_kernel_address / cached_kernel_address symbols to use it
+# uncached_kernel_address symbol to use it
 #
 config ARCH_HAS_UNCACHED_SEGMENT
 	select ARCH_HAS_DMA_PREP_COHERENT
diff --git a/arch/microblaze/mm/consistent.c b/arch/microblaze/mm/consistent.c
index 8c5f0c332d8b..cede7c5e8135 100644
--- a/arch/microblaze/mm/consistent.c
+++ b/arch/microblaze/mm/consistent.c
@@ -49,11 +49,4 @@ void *uncached_kernel_address(void *ptr)
 		pr_warn("ERROR: Your cache coherent area is CACHED!!!\n");
 	return (void *)addr;
 }
-
-void *cached_kernel_address(void *ptr)
-{
-	unsigned long addr = (unsigned long)ptr;
-
-	return (void *)(addr & ~UNCACHED_SHADOW_MASK);
-}
 #endif /* CONFIG_MMU */
diff --git a/arch/mips/mm/dma-noncoherent.c b/arch/mips/mm/dma-noncoherent.c
index dc42ffc83825..77dce28ad0a0 100644
--- a/arch/mips/mm/dma-noncoherent.c
+++ b/arch/mips/mm/dma-noncoherent.c
@@ -54,11 +54,6 @@ void *uncached_kernel_address(void *addr)
 	return (void *)(__pa(addr) + UNCAC_BASE);
 }
 
-void *cached_kernel_address(void *addr)
-{
-	return __va(addr) - UNCAC_BASE;
-}
-
 static inline void dma_sync_virt(void *addr, size_t size,
 		enum dma_data_direction dir)
 {
diff --git a/arch/nios2/mm/dma-mapping.c b/arch/nios2/mm/dma-mapping.c
index 0ed711e37902..f30f2749257c 100644
--- a/arch/nios2/mm/dma-mapping.c
+++ b/arch/nios2/mm/dma-mapping.c
@@ -75,13 +75,3 @@ void *uncached_kernel_address(void *ptr)
 
 	return (void *)ptr;
 }
-
-void *cached_kernel_address(void *ptr)
-{
-	unsigned long addr = (unsigned long)ptr;
-
-	addr &= ~CONFIG_NIOS2_IO_REGION_BASE;
-	addr |= CONFIG_NIOS2_KERNEL_REGION_BASE;
-
-	return (void *)ptr;
-}
diff --git a/arch/xtensa/kernel/pci-dma.c b/arch/xtensa/kernel/pci-dma.c
index 72b6222daa0b..6a685545d5c9 100644
--- a/arch/xtensa/kernel/pci-dma.c
+++ b/arch/xtensa/kernel/pci-dma.c
@@ -88,18 +88,12 @@ void arch_dma_prep_coherent(struct page *page, size_t size)
 
 /*
  * Memory caching is platform-dependent in noMMU xtensa configurations.
- * The following two functions should be implemented in platform code
- * in order to enable coherent DMA memory operations when CONFIG_MMU is not
- * enabled.
+ * This function should be implemented in platform code in order to enable
+ * coherent DMA memory operations when CONFIG_MMU is not enabled.
  */
 #ifdef CONFIG_MMU
 void *uncached_kernel_address(void *p)
 {
 	return p + XCHAL_KSEG_BYPASS_VADDR - XCHAL_KSEG_CACHED_VADDR;
 }
-
-void *cached_kernel_address(void *p)
-{
-	return p + XCHAL_KSEG_CACHED_VADDR - XCHAL_KSEG_BYPASS_VADDR;
-}
 #endif /* CONFIG_MMU */
diff --git a/include/linux/dma-noncoherent.h b/include/linux/dma-noncoherent.h
index ca9b5770caee..b6b72e19b0cd 100644
--- a/include/linux/dma-noncoherent.h
+++ b/include/linux/dma-noncoherent.h
@@ -109,6 +109,5 @@ static inline void arch_dma_prep_coherent(struct page *page, size_t size)
 #endif /* CONFIG_ARCH_HAS_DMA_PREP_COHERENT */
 
 void *uncached_kernel_address(void *addr);
-void *cached_kernel_address(void *addr);
 
 #endif /* _LINUX_DMA_NONCOHERENT_H */
-- 
2.24.1

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[PATCH 2/5] dma-direct: consolidate the error handling in dma_direct_alloc_pages

[Christoph Hellwig]

Use a goto label to merge two error return cases.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 kernel/dma/direct.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index ac7956c38f69..9dfcc7be4903 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -157,11 +157,8 @@ void *dma_direct_alloc_pages(struct device *dev, size_t size,
 		ret = dma_common_contiguous_remap(page, PAGE_ALIGN(size),
 				dma_pgprot(dev, PAGE_KERNEL, attrs),
 				__builtin_return_address(0));
-		if (!ret) {
-			dma_free_contiguous(dev, page, size);
-			return ret;
-		}
-
+		if (!ret)
+			goto out_free_pages;
 		memset(ret, 0, size);
 		goto done;
 	}
@@ -174,8 +171,7 @@ void *dma_direct_alloc_pages(struct device *dev, size_t size,
 		 * so log an error and fail.
 		 */
 		dev_info(dev, "Rejecting highmem page from CMA.\n");
-		dma_free_contiguous(dev, page, size);
-		return NULL;
+		goto out_free_pages;
 	}
 
 	ret = page_address(page);
@@ -195,6 +191,9 @@ void *dma_direct_alloc_pages(struct device *dev, size_t size,
 	else
 		*dma_handle = phys_to_dma(dev, page_to_phys(page));
 	return ret;
+out_free_pages:
+	dma_free_contiguous(dev, page, size);
+	return NULL;
 }
 
 void dma_direct_free_pages(struct device *dev, size_t size, void *cpu_addr,
-- 
2.24.1

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[PATCH 3/5] dma-direct: make uncached_kernel_address more general

[Christoph Hellwig]

Rename the symbol to arch_dma_set_uncached, and pass a size to it as
well as allow an error return.  That will allow reusing this hook for
in-place pagetable remapping.

As the in-place remap doesn't always require an explicit cache flush,
also detangle ARCH_HAS_DMA_PREP_COHERENT from ARCH_HAS_DMA_SET_UNCACHED.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 arch/Kconfig                    |  8 ++++----
 arch/microblaze/Kconfig         |  2 +-
 arch/microblaze/mm/consistent.c |  2 +-
 arch/mips/Kconfig               |  3 ++-
 arch/mips/mm/dma-noncoherent.c  |  2 +-
 arch/nios2/Kconfig              |  3 ++-
 arch/nios2/mm/dma-mapping.c     |  2 +-
 arch/xtensa/Kconfig             |  2 +-
 arch/xtensa/kernel/pci-dma.c    |  2 +-
 include/linux/dma-noncoherent.h |  2 +-
 kernel/dma/direct.c             | 10 ++++++----
 11 files changed, 21 insertions(+), 17 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 7994b239f155..090cfe0c82a7 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -248,11 +248,11 @@ config ARCH_HAS_SET_DIRECT_MAP
 	bool
 
 #
-# Select if arch has an uncached kernel segment and provides the
-# uncached_kernel_address symbol to use it
+# Select if the architecture provides the arch_dma_set_uncached symbol to
+# either provide an uncached segement alias for a DMA allocation, or
+# to remap the page tables in place.
 #
-config ARCH_HAS_UNCACHED_SEGMENT
-	select ARCH_HAS_DMA_PREP_COHERENT
+config ARCH_HAS_DMA_SET_UNCACHED
 	bool
 
 # Select if arch init_task must go in the __init_task_data section
diff --git a/arch/microblaze/Kconfig b/arch/microblaze/Kconfig
index 6a331bd57ea8..9606c244b5b8 100644
--- a/arch/microblaze/Kconfig
+++ b/arch/microblaze/Kconfig
@@ -8,7 +8,7 @@ config MICROBLAZE
 	select ARCH_HAS_GCOV_PROFILE_ALL
 	select ARCH_HAS_SYNC_DMA_FOR_CPU
 	select ARCH_HAS_SYNC_DMA_FOR_DEVICE
-	select ARCH_HAS_UNCACHED_SEGMENT if !MMU
+	select ARCH_HAS_DMA_SET_UNCACHED if !MMU
 	select ARCH_MIGHT_HAVE_PC_PARPORT
 	select ARCH_WANT_IPC_PARSE_VERSION
 	select BUILDTIME_TABLE_SORT
diff --git a/arch/microblaze/mm/consistent.c b/arch/microblaze/mm/consistent.c
index cede7c5e8135..e09b66e43cb6 100644
--- a/arch/microblaze/mm/consistent.c
+++ b/arch/microblaze/mm/consistent.c
@@ -40,7 +40,7 @@ void arch_dma_prep_coherent(struct page *page, size_t size)
 #define UNCACHED_SHADOW_MASK 0
 #endif /* CONFIG_XILINX_UNCACHED_SHADOW */
 
-void *uncached_kernel_address(void *ptr)
+void *arch_dma_set_uncached(void *ptr, size_t size)
 {
 	unsigned long addr = (unsigned long)ptr;
 
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 797d7f1ad5fe..489185db501e 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -1187,8 +1187,9 @@ config DMA_NONCOHERENT
 	# significant advantages.
 	#
 	select ARCH_HAS_DMA_WRITE_COMBINE
+	select ARCH_HAS_DMA_PREP_COHERENT
 	select ARCH_HAS_SYNC_DMA_FOR_DEVICE
-	select ARCH_HAS_UNCACHED_SEGMENT
+	select ARCH_HAS_DMA_SET_UNCACHED
 	select DMA_NONCOHERENT_MMAP
 	select DMA_NONCOHERENT_CACHE_SYNC
 	select NEED_DMA_MAP_STATE
diff --git a/arch/mips/mm/dma-noncoherent.c b/arch/mips/mm/dma-noncoherent.c
index 77dce28ad0a0..fcea92d95d86 100644
--- a/arch/mips/mm/dma-noncoherent.c
+++ b/arch/mips/mm/dma-noncoherent.c
@@ -49,7 +49,7 @@ void arch_dma_prep_coherent(struct page *page, size_t size)
 	dma_cache_wback_inv((unsigned long)page_address(page), size);
 }
 
-void *uncached_kernel_address(void *addr)
+void *arch_dma_set_uncached(void *addr, size_t size)
 {
 	return (void *)(__pa(addr) + UNCAC_BASE);
 }
diff --git a/arch/nios2/Kconfig b/arch/nios2/Kconfig
index 44b5da37e8bd..2fc4ed210b5f 100644
--- a/arch/nios2/Kconfig
+++ b/arch/nios2/Kconfig
@@ -2,9 +2,10 @@
 config NIOS2
 	def_bool y
 	select ARCH_32BIT_OFF_T
+	select ARCH_HAS_DMA_PREP_COHERENT
 	select ARCH_HAS_SYNC_DMA_FOR_CPU
 	select ARCH_HAS_SYNC_DMA_FOR_DEVICE
-	select ARCH_HAS_UNCACHED_SEGMENT
+	select ARCH_HAS_DMA_SET_UNCACHED
 	select ARCH_NO_SWAP
 	select TIMER_OF
 	select GENERIC_ATOMIC64
diff --git a/arch/nios2/mm/dma-mapping.c b/arch/nios2/mm/dma-mapping.c
index f30f2749257c..fd887d5f3f9a 100644
--- a/arch/nios2/mm/dma-mapping.c
+++ b/arch/nios2/mm/dma-mapping.c
@@ -67,7 +67,7 @@ void arch_dma_prep_coherent(struct page *page, size_t size)
 	flush_dcache_range(start, start + size);
 }
 
-void *uncached_kernel_address(void *ptr)
+void *arch_dma_set_uncached(void *ptr, size_t size)
 {
 	unsigned long addr = (unsigned long)ptr;
 
diff --git a/arch/xtensa/Kconfig b/arch/xtensa/Kconfig
index 32ee759a3fda..de229424b659 100644
--- a/arch/xtensa/Kconfig
+++ b/arch/xtensa/Kconfig
@@ -6,7 +6,7 @@ config XTENSA
 	select ARCH_HAS_DMA_PREP_COHERENT if MMU
 	select ARCH_HAS_SYNC_DMA_FOR_CPU if MMU
 	select ARCH_HAS_SYNC_DMA_FOR_DEVICE if MMU
-	select ARCH_HAS_UNCACHED_SEGMENT if MMU
+	select ARCH_HAS_DMA_SET_UNCACHED if MMU
 	select ARCH_USE_QUEUED_RWLOCKS
 	select ARCH_USE_QUEUED_SPINLOCKS
 	select ARCH_WANT_FRAME_POINTERS
diff --git a/arch/xtensa/kernel/pci-dma.c b/arch/xtensa/kernel/pci-dma.c
index 6a685545d5c9..17c4384f8495 100644
--- a/arch/xtensa/kernel/pci-dma.c
+++ b/arch/xtensa/kernel/pci-dma.c
@@ -92,7 +92,7 @@ void arch_dma_prep_coherent(struct page *page, size_t size)
  * coherent DMA memory operations when CONFIG_MMU is not enabled.
  */
 #ifdef CONFIG_MMU
-void *uncached_kernel_address(void *p)
+void *arch_dma_set_uncached(void *p, size_t size)
 {
 	return p + XCHAL_KSEG_BYPASS_VADDR - XCHAL_KSEG_CACHED_VADDR;
 }
diff --git a/include/linux/dma-noncoherent.h b/include/linux/dma-noncoherent.h
index b6b72e19b0cd..1a4039506673 100644
--- a/include/linux/dma-noncoherent.h
+++ b/include/linux/dma-noncoherent.h
@@ -108,6 +108,6 @@ static inline void arch_dma_prep_coherent(struct page *page, size_t size)
 }
 #endif /* CONFIG_ARCH_HAS_DMA_PREP_COHERENT */
 
-void *uncached_kernel_address(void *addr);
+void *arch_dma_set_uncached(void *addr, size_t size);
 
 #endif /* _LINUX_DMA_NONCOHERENT_H */
diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 9dfcc7be4903..f01a8191fd59 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -180,10 +180,12 @@ void *dma_direct_alloc_pages(struct device *dev, size_t size,
 
 	memset(ret, 0, size);
 
-	if (IS_ENABLED(CONFIG_ARCH_HAS_UNCACHED_SEGMENT) &&
+	if (IS_ENABLED(CONFIG_ARCH_HAS_DMA_SET_UNCACHED) &&
 	    dma_alloc_need_uncached(dev, attrs)) {
 		arch_dma_prep_coherent(page, size);
-		ret = uncached_kernel_address(ret);
+		ret = arch_dma_set_uncached(ret, size);
+		if (IS_ERR(ret))
+			goto out_free_pages;
 	}
 done:
 	if (force_dma_unencrypted(dev))
@@ -224,7 +226,7 @@ void dma_direct_free_pages(struct device *dev, size_t size, void *cpu_addr,
 void *dma_direct_alloc(struct device *dev, size_t size,
 		dma_addr_t *dma_handle, gfp_t gfp, unsigned long attrs)
 {
-	if (!IS_ENABLED(CONFIG_ARCH_HAS_UNCACHED_SEGMENT) &&
+	if (!IS_ENABLED(CONFIG_ARCH_HAS_DMA_SET_UNCACHED) &&
 	    !IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) &&
 	    dma_alloc_need_uncached(dev, attrs))
 		return arch_dma_alloc(dev, size, dma_handle, gfp, attrs);
@@ -234,7 +236,7 @@ void *dma_direct_alloc(struct device *dev, size_t size,
 void dma_direct_free(struct device *dev, size_t size,
 		void *cpu_addr, dma_addr_t dma_addr, unsigned long attrs)
 {
-	if (!IS_ENABLED(CONFIG_ARCH_HAS_UNCACHED_SEGMENT) &&
+	if (!IS_ENABLED(CONFIG_ARCH_HAS_DMA_SET_UNCACHED) &&
 	    !IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) &&
 	    dma_alloc_need_uncached(dev, attrs))
 		arch_dma_free(dev, size, cpu_addr, dma_addr, attrs);
-- 
2.24.1

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[PATCH 4/5] dma-direct: provide a arch_dma_clear_uncached hook

[Christoph Hellwig]

This allows the arch code to reset the page tables to cached access when
freeing a dma coherent allocation that was set to uncached using
arch_dma_set_uncached.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 arch/Kconfig                    | 7 +++++++
 include/linux/dma-noncoherent.h | 1 +
 kernel/dma/direct.c             | 2 ++
 3 files changed, 10 insertions(+)

diff --git a/arch/Kconfig b/arch/Kconfig
index 090cfe0c82a7..c26302f90c96 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -255,6 +255,13 @@ config ARCH_HAS_SET_DIRECT_MAP
 config ARCH_HAS_DMA_SET_UNCACHED
 	bool
 
+#
+# Select if the architectures provides the arch_dma_clear_uncached symbol
+# to undo an in-place page table remap for uncached access.
+#
+config ARCH_HAS_DMA_CLEAR_UNCACHED
+	bool
+
 # Select if arch init_task must go in the __init_task_data section
 config ARCH_TASK_STRUCT_ON_STACK
 	bool
diff --git a/include/linux/dma-noncoherent.h b/include/linux/dma-noncoherent.h
index 1a4039506673..b59f1b6be3e9 100644
--- a/include/linux/dma-noncoherent.h
+++ b/include/linux/dma-noncoherent.h
@@ -109,5 +109,6 @@ static inline void arch_dma_prep_coherent(struct page *page, size_t size)
 #endif /* CONFIG_ARCH_HAS_DMA_PREP_COHERENT */
 
 void *arch_dma_set_uncached(void *addr, size_t size);
+void arch_dma_clear_uncached(void *addr, size_t size);
 
 #endif /* _LINUX_DMA_NONCOHERENT_H */
diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index f01a8191fd59..a8560052a915 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -219,6 +219,8 @@ void dma_direct_free_pages(struct device *dev, size_t size, void *cpu_addr,
 
 	if (IS_ENABLED(CONFIG_DMA_REMAP) && is_vmalloc_addr(cpu_addr))
 		vunmap(cpu_addr);
+	else if (IS_ENABLED(CONFIG_ARCH_HAS_DMA_CLEAR_UNCACHED))
+		arch_dma_clear_uncached(cpu_addr, size);
 
 	dma_free_contiguous(dev, dma_direct_to_page(dev, dma_addr), size);
 }
-- 
2.24.1

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[PATCH 5/5] openrisc: use the generic in-place uncached DMA allocator

[Christoph Hellwig]

Switch openrisc to use the dma-direct allocator and just provide the
hooks for setting memory uncached or cached.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 arch/openrisc/Kconfig      |  2 ++
 arch/openrisc/kernel/dma.c | 55 +++++++-------------------------------
 2 files changed, 12 insertions(+), 45 deletions(-)

diff --git a/arch/openrisc/Kconfig b/arch/openrisc/Kconfig
index 1928e061ff96..7e94fe37cb2f 100644
--- a/arch/openrisc/Kconfig
+++ b/arch/openrisc/Kconfig
@@ -7,6 +7,8 @@
 config OPENRISC
 	def_bool y
 	select ARCH_32BIT_OFF_T
+	select ARCH_HAS_DMA_SET_UNCACHED
+	select ARCH_HAS_DMA_CLEAR_UNCACHED
 	select ARCH_HAS_SYNC_DMA_FOR_DEVICE
 	select OF
 	select OF_EARLY_FLATTREE
diff --git a/arch/openrisc/kernel/dma.c b/arch/openrisc/kernel/dma.c
index adec711ad39d..c152a68811dd 100644
--- a/arch/openrisc/kernel/dma.c
+++ b/arch/openrisc/kernel/dma.c
@@ -11,8 +11,6 @@
  * Copyright (C) 2010-2011 Jonas Bonn <jonas@southpole.se>
  *
  * DMA mapping callbacks...
- * As alloc_coherent is the only DMA callback being used currently, that's
- * the only thing implemented properly.  The rest need looking into...
  */
 
 #include <linux/dma-noncoherent.h>
@@ -67,62 +65,29 @@ static const struct mm_walk_ops clear_nocache_walk_ops = {
 	.pte_entry		= page_clear_nocache,
 };
 
-/*
- * Alloc "coherent" memory, which for OpenRISC means simply uncached.
- *
- * This function effectively just calls __get_free_pages, sets the
- * cache-inhibit bit on those pages, and makes sure that the pages are
- * flushed out of the cache before they are used.
- *
- * If the NON_CONSISTENT attribute is set, then this function just
- * returns "normal", cachable memory.
- *
- * There are additional flags WEAK_ORDERING and WRITE_COMBINE to take
- * into consideration here, too.  All current known implementations of
- * the OR1K support only strongly ordered memory accesses, so that flag
- * is being ignored for now; uncached but write-combined memory is a
- * missing feature of the OR1K.
- */
-void *
-arch_dma_alloc(struct device *dev, size_t size, dma_addr_t *dma_handle,
-		gfp_t gfp, unsigned long attrs)
+void *arch_dma_set_uncached(void *cpu_addr, size_t size)
 {
-	unsigned long va;
-	void *page;
-
-	page = alloc_pages_exact(size, gfp | __GFP_ZERO);
-	if (!page)
-		return NULL;
-
-	/* This gives us the real physical address of the first page. */
-	*dma_handle = __pa(page);
-
-	va = (unsigned long)page;
+	unsigned long va = (unsigned long)cpu_addr;
+	int error;
 
 	/*
 	 * We need to iterate through the pages, clearing the dcache for
 	 * them and setting the cache-inhibit bit.
 	 */
-	if (walk_page_range(&init_mm, va, va + size, &set_nocache_walk_ops,
-			NULL)) {
-		free_pages_exact(page, size);
-		return NULL;
-	}
-
-	return (void *)va;
+	error = walk_page_range(&init_mm, va, va + size, &set_nocache_walk_ops,
+			NULL);
+	if (error)
+		return ERR_PTR(error);
+	return cpu_addr;
 }
 
-void
-arch_dma_free(struct device *dev, size_t size, void *vaddr,
-		dma_addr_t dma_handle, unsigned long attrs)
+void arch_dma_clear_uncached(void *cpu_addr, size_t size)
 {
-	unsigned long va = (unsigned long)vaddr;
+	unsigned long va = (unsigned long)cpu_addr;
 
 	/* walk_page_range shouldn't be able to fail here */
 	WARN_ON(walk_page_range(&init_mm, va, va + size,
 			&clear_nocache_walk_ops, NULL));
-
-	free_pages_exact(vaddr, size);
 }
 
 void arch_sync_dma_for_device(phys_addr_t addr, size_t size,
-- 
2.24.1

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Re: [PATCH 4/5] dma-direct: provide a arch_dma_clear_uncached hook

[Ira Weiny]

On Mon, Feb 24, 2020 at 11:44:44AM -0800, Christoph Hellwig wrote:
> This allows the arch code to reset the page tables to cached access when
> freeing a dma coherent allocation that was set to uncached using
> arch_dma_set_uncached.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  arch/Kconfig                    | 7 +++++++
>  include/linux/dma-noncoherent.h | 1 +
>  kernel/dma/direct.c             | 2 ++
>  3 files changed, 10 insertions(+)
> 
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 090cfe0c82a7..c26302f90c96 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -255,6 +255,13 @@ config ARCH_HAS_SET_DIRECT_MAP
>  config ARCH_HAS_DMA_SET_UNCACHED
>  	bool
>  
> +#
> +# Select if the architectures provides the arch_dma_clear_uncached symbol
> +# to undo an in-place page table remap for uncached access.
> +#
> +config ARCH_HAS_DMA_CLEAR_UNCACHED
> +	bool
> +
>  # Select if arch init_task must go in the __init_task_data section
>  config ARCH_TASK_STRUCT_ON_STACK
>  	bool
> diff --git a/include/linux/dma-noncoherent.h b/include/linux/dma-noncoherent.h
> index 1a4039506673..b59f1b6be3e9 100644
> --- a/include/linux/dma-noncoherent.h
> +++ b/include/linux/dma-noncoherent.h
> @@ -109,5 +109,6 @@ static inline void arch_dma_prep_coherent(struct page *page, size_t size)
>  #endif /* CONFIG_ARCH_HAS_DMA_PREP_COHERENT */
>  
>  void *arch_dma_set_uncached(void *addr, size_t size);
> +void arch_dma_clear_uncached(void *addr, size_t size);
>  
>  #endif /* _LINUX_DMA_NONCOHERENT_H */
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index f01a8191fd59..a8560052a915 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -219,6 +219,8 @@ void dma_direct_free_pages(struct device *dev, size_t size, void *cpu_addr,
>  
>  	if (IS_ENABLED(CONFIG_DMA_REMAP) && is_vmalloc_addr(cpu_addr))
>  		vunmap(cpu_addr);
> +	else if (IS_ENABLED(CONFIG_ARCH_HAS_DMA_CLEAR_UNCACHED))
> +		arch_dma_clear_uncached(cpu_addr, size);

Isn't using arch_dma_clear_uncached() before patch 5 going to break
bisectability?

Ira

>  
>  	dma_free_contiguous(dev, dma_direct_to_page(dev, dma_addr), size);
>  }
> -- 
> 2.24.1
> 
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Re: [PATCH 4/5] dma-direct: provide a arch_dma_clear_uncached hook

[Christoph Hellwig]

On Mon, Feb 24, 2020 at 01:53:28PM -0800, Ira Weiny wrote:
> > +	else if (IS_ENABLED(CONFIG_ARCH_HAS_DMA_CLEAR_UNCACHED))
> > +		arch_dma_clear_uncached(cpu_addr, size);
> 
> Isn't using arch_dma_clear_uncached() before patch 5 going to break
> bisectability?

Only if ARCH_HAS_DMA_CLEAR_UNCACHED is selected by anything, which
only happens in patch 5.
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Re: [PATCH 5/5] openrisc: use the generic in-place uncached DMA allocator

[Stafford Horne]

On Mon, Feb 24, 2020 at 11:44:45AM -0800, Christoph Hellwig wrote:
> Switch openrisc to use the dma-direct allocator and just provide the
> hooks for setting memory uncached or cached.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Reviewed-by: Stafford Horne <shorne@gmail.com>

I also test booted this series with linux 5.5 on my OpenRISC target.  There are
no issues.  Note, I had an issue with patch 3/5 not cleanly applying with 'git am'
but it worked fine using just patch, I didn't get any other details.

-Stafford
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Re: provide in-place uncached remapping for dma-direct v2

[Robin Murphy]

On 24/02/2020 7:44 pm, Christoph Hellwig wrote:
> Hi all,
> 
> this series provides support for remapping places uncached in-place in
> the generic dma-direct code, and moves openrisc over from its own
> in-place remapping scheme.  The arm64 folks also had interest in such
> a scheme to avoid problems with speculating into cache aliases.
> 
> Also all architectures that always use small page mappings for the
> kernel and have non-coherent DMA should look into enabling this
> scheme, as it is much more efficient than the vmap remapping.
> 
> Changes since v1:
>   - share the arch hook for inline remap and uncached segment support
> 

For the whole series:

Reviewed-by: Robin Murphy <robin.murphy@arm.com>

I think we might ultimately want to fiddle around a bit more in 
dma_direct_alloc_pages() to give ARCH_HAS_DMA_SET_UNCACHED clear 
precedence over DMA_DIRECT_REMAP if they have to coexist, but let's land 
these patches first as a solid foundation.

Thanks,
Robin.
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