arm64: Remove pgprot_dmacoherent()

Since this macro is identical to pgprot_writecombine() and is only used
in a single place, remove it completely to avoid confusion. On ARMv7+
processors, the coherent DMA mapping must be Normal NonCacheable (a.k.a.
writecombine) to avoid mismatched hardware attribute aliases (with the
kernel linear mapping as Normal Cacheable).

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/pgtable.h

@@ -280,8 +280,6 @@ static inline int has_transparent_hugepage(void)
 	__pgprot_modify(prot, PTE_ATTRINDX_MASK, PTE_ATTRINDX(MT_DEVICE_nGnRnE) | PTE_PXN | PTE_UXN)
 #define pgprot_writecombine(prot) \
 	__pgprot_modify(prot, PTE_ATTRINDX_MASK, PTE_ATTRINDX(MT_NORMAL_NC) | PTE_PXN | PTE_UXN)
-#define pgprot_dmacoherent(prot) \
-	__pgprot_modify(prot, PTE_ATTRINDX_MASK, PTE_ATTRINDX(MT_NORMAL_NC) | PTE_PXN | PTE_UXN)
 #define __HAVE_PHYS_MEM_ACCESS_PROT
 struct file;
 extern pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,

arch/arm64/mm/dma-mapping.c

@@ -33,10 +33,8 @@ EXPORT_SYMBOL(dma_ops);
 static pgprot_t __get_dma_pgprot(struct dma_attrs *attrs, pgprot_t prot,
 				 bool coherent)
 {
-	if (dma_get_attr(DMA_ATTR_WRITE_COMBINE, attrs))
+	if (!coherent || dma_get_attr(DMA_ATTR_WRITE_COMBINE, attrs))
 		return pgprot_writecombine(prot);
-	else if (!coherent)
-		return pgprot_dmacoherent(prot);
 	return prot;
 }