* __dma_sync_page() implementation for systems using highmem.
* In this case, each page of a buffer must be kmapped/kunmapped
* in order to have a virtual address for __dma_sync(). This must
* __dma_sync_page() implementation for systems using highmem.
* In this case, each page of a buffer must be kmapped/kunmapped
* in order to have a virtual address for __dma_sync(). This must