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SubjectRe: [PATCH 3/4] ARC: refactor arch/arc/mm/dma.c
On Tue, Jul 24, 2018 at 01:10:00PM +0300, Eugeniy Paltsev wrote:
> Refactoring, no functional change intended.

Might be worth explaining a bit why you are refactoring it (i.e. what is the
benefit).

>
> Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
> ---
> arch/arc/mm/dma.c | 28 ++++++++++------------------
> 1 file changed, 10 insertions(+), 18 deletions(-)
>
> diff --git a/arch/arc/mm/dma.c b/arch/arc/mm/dma.c
> index b693818cd8e5..46584c7c2858 100644
> --- a/arch/arc/mm/dma.c
> +++ b/arch/arc/mm/dma.c
> @@ -27,30 +27,24 @@ void *arch_dma_alloc(struct device *dev, size_t size, dma_addr_t *dma_handle,
> struct page *page;
> phys_addr_t paddr;
> void *kvaddr;
> - int need_coh = 1, need_kvaddr = 0;
> + bool need_coh = !(attrs & DMA_ATTR_NON_CONSISTENT);
>
> page = alloc_pages(gfp, order);
> if (!page)
> return NULL;
>
> /* This is linear addr (0x8000_0000 based) */
> paddr = page_to_phys(page);
>
> *dma_handle = paddr;
>
> + /*
> + * - A coherent buffer needs MMU mapping to enforce non-cachability
> + * - A highmem page needs a virtual handle (hence MMU mapping)
> + * independent of cachability.
> + * kvaddr is kernel Virtual address (0x7000_0000 based)
> + */
> + if (PageHighMem(page) || need_coh) {

dma_alloc_attrs clears __GFP_HIGHMEM from the passed in gfp mask, so
you'll never get a highmem page here.

That also means you can merge this conditional with the one for the cache
writeback and invalidation and kill the need_coh flag entirely.

> kvaddr = ioremap_nocache(paddr, size);
> if (kvaddr == NULL) {
> __free_pages(page, order);
> @@ -81,11 +75,9 @@ void arch_dma_free(struct device *dev, size_t size, void *vaddr,
> {
> phys_addr_t paddr = dma_handle;
> struct page *page = virt_to_page(paddr);
> - int is_non_coh = 1;
> -
> - is_non_coh = (attrs & DMA_ATTR_NON_CONSISTENT);
> + bool is_coh = !(attrs & DMA_ATTR_NON_CONSISTENT);
>
> - if (PageHighMem(page) || !is_non_coh)
> + if (PageHighMem(page) || is_coh)
> iounmap((void __force __iomem *)vaddr);
>

Same here.

Also if you clean this up it would be great to take the per-device pfn offset
into account, even if that isn't used anywhere on arc yet, that is call
phys_to_dma and dma_to_phys to convert to an from the dma address.

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