[PATCH/RFC 2/7] xtensa: 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(). xtensa with CONFIG_HIGHMEM uses
HASHED_PAGE_VIRTUAL, so page_address() returns NULL for a highmem page
that is not kmapped, and the cache operation then works 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.

Fix this by reusing do_cache_op(), which the arch_sync_dma_for_*() hooks
already use and which maps highmem pages one page at a time with
kmap_atomic(). For lowmem pages it does a single cache operation over
the whole range, so the behaviour is unchanged there. A small wrapper
is needed because __flush_invalidate_dcache_range() is a macro on cores
with a write-through data cache.

Fixes: 0f665b9e2a6d ("xtensa: use the generic uncached segment support")
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
---
 arch/xtensa/kernel/pci-dma.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/xtensa/kernel/pci-dma.c b/arch/xtensa/kernel/pci-dma.c
index e1c00ec37eed..41467a1ba068 100644
--- a/arch/xtensa/kernel/pci-dma.c
+++ b/arch/xtensa/kernel/pci-dma.c
@@ -80,9 +80,19 @@ void arch_sync_dma_for_device(phys_addr_t paddr, size_t size,
 	}
 }
 
+/*
+ * __flush_invalidate_dcache_range() may be a macro on cores with a
+ * write-through data cache, so it cannot be passed to do_cache_op().
+ */
+static void flush_invalidate_dcache_range(unsigned long start,
+					  unsigned long size)
+{
+	__flush_invalidate_dcache_range(start, size);
+}
+
 void arch_dma_prep_coherent(struct page *page, size_t size)
 {
-	__flush_invalidate_dcache_range((unsigned long)page_address(page), size);
+	do_cache_op(page_to_phys(page), size, flush_invalidate_dcache_range);
 }
 
 /*
-- 
2.43.0