[PATCH/RFC 3/7] MIPS: mm: handle highmem pages in arch_dma_prep_coherent()

[Marek Szyprowski <m.szyprowski@samsung.com>]

arch_dma_prep_coherent() performs the cache maintenance on the address
returned by page_address(). On 32-bit MIPS with CONFIG_HIGHMEM the kernel
uses HASHED_PAGE_VIRTUAL, so page_address() returns NULL for a highmem
page that is not kmapped, and dma_cache_wback_inv() then operates on
the virtual range starting at 0 instead of the buffer, leaving any dirty
cache lines of the buffer in place.

Highmem pages do reach this function: dma_alloc_contiguous() can return
a highmem CMA page, which dma_direct_alloc() handles by forcing the remap
path and calling arch_dma_prep_coherent() on that page before creating
the uncached mapping. Since commit f5ff79fddf0e ("dma-mapping: remove
CONFIG_DMA_REMAP") this path is available on all MMU architectures,
including MIPS, which previously rejected highmem CMA pages.

Fix this by reusing dma_sync_phys(), which already handles highmem pages
by mapping them one page at a time with kmap_atomic(). For lowmem pages
it does a single dma_cache_wback_inv() over the whole range, so the
behaviour is unchanged there.

Fixes: f5ff79fddf0e ("dma-mapping: remove CONFIG_DMA_REMAP")
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
---
 arch/mips/mm/dma-noncoherent.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/mips/mm/dma-noncoherent.c b/arch/mips/mm/dma-noncoherent.c
index 30ef3e247eb7..d8e5bc85bb3b 100644
--- a/arch/mips/mm/dma-noncoherent.c
+++ b/arch/mips/mm/dma-noncoherent.c
@@ -44,11 +44,6 @@ static inline bool cpu_needs_post_dma_flush(void)
 	}
 }
 
-void arch_dma_prep_coherent(struct page *page, size_t size)
-{
-	dma_cache_wback_inv((unsigned long)page_address(page), size);
-}
-
 void *arch_dma_set_uncached(void *addr, size_t size)
 {
 	return (void *)(__pa(addr) + UNCAC_BASE);
@@ -127,6 +122,11 @@ void arch_sync_dma_for_device(phys_addr_t paddr, size_t size,
 	dma_sync_phys(paddr, size, dir, true);
 }
 
+void arch_dma_prep_coherent(struct page *page, size_t size)
+{
+	dma_sync_phys(page_to_phys(page), size, DMA_BIDIRECTIONAL, true);
+}
+
 #ifdef CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU
 void arch_sync_dma_for_cpu(phys_addr_t paddr, size_t size,
 		enum dma_data_direction dir)
-- 
2.43.0