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SubjectRe: [PATCH 4/9] dma-mapping: move the arm64 ncoherent alloc/free support to common code
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On 05/11/2018 12:19, Christoph Hellwig wrote:
> The arm64 codebase to implement coherent dma allocation for architectures
> with non-coherent DMA is a good start for a generic implementation, given
> that is uses the generic remap helpers, provides the atomic pool for
> allocations that can't sleep and still is realtively simple and well
> tested. Move it to kernel/dma and allow architectures to opt into it
> using a config symbol. Architectures just need to provide a new
> arch_dma_prep_coherent helper to writeback an invalidate the caches
> for any memory that gets remapped for uncached access.

It's a bit yuck that we now end up with arch_* hooks being a mix of arch
code and not-actually-arch-code, but I guess there's some hope of coming
back and streamlining things in future once all the big moves are done.

I can't really be bothered to nitpick the typos above and the slight
inconsistencies in some of the cosmetic code changes, but one worthwhile
thing stands out...

> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> arch/arm64/Kconfig | 2 +-
> arch/arm64/mm/dma-mapping.c | 184 ++------------------------------
> include/linux/dma-mapping.h | 5 +
> include/linux/dma-noncoherent.h | 2 +
> kernel/dma/Kconfig | 6 ++
> kernel/dma/remap.c | 158 ++++++++++++++++++++++++++-
> 6 files changed, 181 insertions(+), 176 deletions(-)

[...]

> +void *dma_alloc_from_pool(size_t size, struct page **ret_page, gfp_t flags)
> +{
> + unsigned long val;
> + void *ptr = NULL;
> +
> + if (!atomic_pool) {
> + WARN(1, "coherent pool not initialised!\n");
> + return NULL;
> + }
> +
> + val = gen_pool_alloc(atomic_pool, size);
> + if (val) {
> + phys_addr_t phys = gen_pool_virt_to_phys(atomic_pool, val);
> +
> + *ret_page = phys_to_page(phys);

Looks like phys_to_page() isn't particularly portable, so we probably
want an explicit pfn_to_page(__phys_to_pfn(phys)) here. Otherwise, the
fundamental refactoring looks OK.

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

[ In fact, looking at phys_to_page(), microblaze, riscv, unicore and
csky (by the end of this series if it's fixed here) don't need to define
it at all; s390 defines it for the sake of a single call in a single
driver; it's used in two other places in arm-related drivers but at
least one of those is clearly wrong. All in all it's quite the sorry mess. ]

> + ptr = (void *)val;
> + memset(ptr, 0, size);
> + }
> +
> + return ptr;
> +}
> +
> +bool dma_free_from_pool(void *start, size_t size)
> +{
> + if (!dma_in_atomic_pool(start, size))
> + return false;
> + gen_pool_free(atomic_pool, (unsigned long)start, size);
> + return true;
> +}
> +
> +void *arch_dma_alloc(struct device *dev, size_t size, dma_addr_t *dma_handle,
> + gfp_t flags, unsigned long attrs)
> +{
> + struct page *page = NULL;
> + void *ret, *kaddr;
> +
> + size = PAGE_ALIGN(size);
> +
> + if (!gfpflags_allow_blocking(flags)) {
> + ret = dma_alloc_from_pool(size, &page, flags);
> + if (!ret)
> + return NULL;
> + *dma_handle = phys_to_dma(dev, page_to_phys(page));
> + return ret;
> + }
> +
> + kaddr = dma_direct_alloc_pages(dev, size, dma_handle, flags, attrs);
> + if (!kaddr)
> + return NULL;
> + page = virt_to_page(kaddr);
> +
> + /* remove any dirty cache lines on the kernel alias */
> + arch_dma_prep_coherent(page, size);
> +
> + /* create a coherent mapping */
> + ret = dma_common_contiguous_remap(page, size, VM_USERMAP,
> + arch_dma_mmap_pgprot(dev, PAGE_KERNEL, attrs),
> + __builtin_return_address(0));
> + if (!ret)
> + dma_direct_free_pages(dev, size, kaddr, *dma_handle, attrs);
> + return ret;
> +}
> +
> +void arch_dma_free(struct device *dev, size_t size, void *vaddr,
> + dma_addr_t dma_handle, unsigned long attrs)
> +{
> + if (!dma_free_from_pool(vaddr, PAGE_ALIGN(size))) {
> + void *kaddr = phys_to_virt(dma_to_phys(dev, dma_handle));
> +
> + vunmap(vaddr);
> + dma_direct_free_pages(dev, size, kaddr, dma_handle, attrs);
> + }
> +}
> +
> +long arch_dma_coherent_to_pfn(struct device *dev, void *cpu_addr,
> + dma_addr_t dma_addr)
> +{
> + return __phys_to_pfn(dma_to_phys(dev, dma_addr));
> +}
> +#endif /* CONFIG_DMA_DIRECT_REMAP */
>

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