Merge branch 'page_pool-DMA-sync'

Lorenzo Bianconi says:

====================
add DMA-sync-for-device capability to page_pool API

Introduce the possibility to sync DMA memory for device in the page_pool API.
This feature allows to sync proper DMA size and not always full buffer
(dma_sync_single_for_device can be very costly).
Please note DMA-sync-for-CPU is still device driver responsibility.
Relying on page_pool DMA sync mvneta driver improves XDP_DROP pps of
about 170Kpps:

- XDP_DROP DMA sync managed by mvneta driver:	~420Kpps
- XDP_DROP DMA sync managed by page_pool API:	~585Kpps

Do not change naming convention for the moment since the changes will hit other
drivers as well. I will address it in another series.

Changes since v4:
- do not allow the driver to set max_len to 0
- convert PP_FLAG_DMA_MAP/PP_FLAG_DMA_SYNC_DEV to BIT() macro

Changes since v3:
- move dma_sync_for_device before putting the page in ptr_ring in
  __page_pool_recycle_into_ring since ptr_ring can be consumed
  concurrently. Simplify the code moving dma_sync_for_device
  before running __page_pool_recycle_direct/__page_pool_recycle_into_ring

Changes since v2:
- rely on PP_FLAG_DMA_SYNC_DEV flag instead of dma_sync

Changes since v1:
- rename sync in dma_sync
- set dma_sync_size to 0xFFFFFFFF in page_pool_recycle_direct and
  page_pool_put_page routines
- Improve documentation
====================

Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

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