Hello,
On 2016-02-19 11:30, Arnd Bergmann wrote:
On Friday 19 February 2016 09:22:44 Marek Szyprowski wrote:
This patch replaces ARM-specific IOMMU-based DMA-mapping implementation
with generic IOMMU DMA-mapping code shared with ARM64 architecture. The
side-effect of this change is a switch from bitmap-based IO address space
management to tree-based code. There should be no functional changes
for drivers, which rely on initialization from generic arch_setup_dna_ops()
interface. Code, which used old arm_iommu_* functions must be updated to
new interface.
Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
I like the overall idea. However, this interface from the iommu
subsystem into architecture specific code:
+/*
+ * The DMA API is built upon the notion of "buffer ownership". A buffer
+ * is either exclusively owned by the CPU (and therefore may be accessed
+ * by it) or exclusively owned by the DMA device. These helper functions
+ * represent the transitions between these two ownership states.
+ *
+ * Note, however, that on later ARMs, this notion does not work due to
+ * speculative prefetches. We model our approach on the assumption that
+ * the CPU does do speculative prefetches, which means we clean caches
+ * before transfers and delay cache invalidation until transfer completion.
+ *
+ */
+extern void __dma_page_cpu_to_dev(struct page *, unsigned long, size_t,
+ enum dma_data_direction);
+extern void __dma_page_dev_to_cpu(struct page *, unsigned long, size_t,
+ enum dma_data_direction);
+
+static inline void arch_flush_page(struct device *dev, const void *virt,
+ phys_addr_t phys)
+{
+ dmac_flush_range(virt, virt + PAGE_SIZE);
+ outer_flush_range(phys, phys + PAGE_SIZE);
+}
+
+static inline void arch_dma_map_area(phys_addr_t phys, size_t size,
+ enum dma_data_direction dir)
+{
+ unsigned int offset = phys & ~PAGE_MASK;
+ __dma_page_cpu_to_dev(phys_to_page(phys & PAGE_MASK), offset, size, dir);
+}
+
+static inline void arch_dma_unmap_area(phys_addr_t phys, size_t size,
+ enum dma_data_direction dir)
+{
+ unsigned int offset = phys & ~PAGE_MASK;
+ __dma_page_dev_to_cpu(phys_to_page(phys & PAGE_MASK), offset, size, dir);
+}
+
+static inline pgprot_t arch_get_dma_pgprot(struct dma_attrs *attrs,
+ pgprot_t prot, bool coherent)
+{
+ if (coherent)
+ return prot;
+
+ prot = dma_get_attr(DMA_ATTR_WRITE_COMBINE, attrs) ?
+ pgprot_writecombine(prot) :
+ pgprot_dmacoherent(prot);
+ return prot;
+}
+
+extern void *arch_alloc_from_atomic_pool(size_t size, struct page **ret_page,
+ gfp_t flags);
+extern bool arch_in_atomic_pool(void *start, size_t size);
+extern int arch_free_from_atomic_pool(void *start, size_t size);
+
+
doesn't feel completely right yet. In particular the arch_flush_page()
interface is probably still too specific to ARM/ARM64 and won't work
that way on other architectures.
I think it would be better to do this either more generic, or less generic:
a) leave the iommu_dma_map_ops definition in the architecture specific
code, but make it call helper functions in the drivers/iommu to do all
of the really generic parts.
b) clarify that this is only applicable to arch/arm and arch/arm64, and
unify things further between these two, as they have very similar
requirements in the CPU architecture.
Some really generic parts are already in iommu/dma-iommu.c and one can build
it's own, non-ARM CPU architecture based IOMMU/DMA-mapping code. Initially I
also wanted to use that generic code on both ARM and ARM64, but it
turned out
that both archs, ARM and ARM64 will duplicate 99% of code, which use this
'generic' functions. This was the reason why I dedided to move all that
common code from arch/{arm,arm64}/mm/dma-mapping.c to
drivers/iommu/dma-iommu-ops.c
I'm not sure if I can design all the changes that need to be made to
drivers/iommu/dma-iommu-ops.c to make it more generic. Maybe when one will
try to use that code with other, non-ARM architecture based arch glue code,
a better abstraction can be developed. For now I would like to keep all this
code in a common place so both arm and arm64 will benefit from improvements
done there.
Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland
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