[ARM] Buffer allocated by dma_alloc_coherent cannot be invalidated/cleaned/flushed by dma_cache_maint

Buffer allocated by dma_alloc_coherent cannot be invalidated/cleaned/flushed by dma_cache_maint, or you will get an BUG()

Buffer allocated by dma_alloc_coherent will have address at 0xfXXX_XXXX

arch/arm/mm/consistent.c

/*
 * Make an area consistent for devices.
 * Note: Drivers should NOT use this function directly, as it will break
 * platforms with CONFIG_DMABOUNCE.
 * Use the driver DMA support - see dma-mapping.h (dma_sync_*)
 */
void dma_cache_maint(const void *start, size_t size, int direction)
{
        const void *end = start + size;
        
        BUG_ON(!virt_addr_valid(start) || !virt_addr_valid(end - 1));
        
        switch (direction) {
        case DMA_FROM_DEVICE:           /* invalidate only */
                dmac_inv_range(start, end);
                outer_inv_range(__pa(start), __pa(end));
                break;
        case DMA_TO_DEVICE:             /* writeback only */
                dmac_clean_range(start, end);
                outer_clean_range(__pa(start), __pa(end));
                break;
        case DMA_BIDIRECTIONAL:         /* writeback and invalidate */
                dmac_flush_range(start, end);
                outer_flush_range(__pa(start), __pa(end));
                break;
        default:
                BUG();
        }
}
EXPORT_SYMBOL(dma_cache_maint);

arch/arm/include/asm/memory.h

#define virt_addr_valid(kaddr) ((unsigned long)(kaddr) >= PAGE_OFFSET && (unsigned long)(kaddr) < (unsigned long)high_memory)

PAGE_OFFSET=0xc000_0000
high_memory=0xd000_0000

PAGE_OFFSET(0xc000_0000) < addr < high_memory(0xd000_0000)