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Some PCI Endpoint controllers integrate an eDMA (embedded DMA).  eDMA can
bypass the outbound memory address translation unit to access all RC memory
space.

Add eDMA support for pci-epf-test.

Depending on HW availability, the EPF test can use either eDMA or general
system DMA controllers to perform DMA. The test tries to use eDMA first and
falls back to general system DMA controllers if there's no eDMA

Separate dma_chan to dma_chan_tx and dma_chan_rx. Search for an eDMA
channel first, then search for a memory-to-memory DMA channel.  If general
memory to memory channels are used, dma_chan_rx = dma_chan_tx.

Add dma_addr_t dma_remote in pci_epf_test_data_transfer() because eDMA uses
remote RC physical address directly.

Add enum dma_transfer_direction dir in pci_epf_test_data_transfer() because
eDMA chooses the correct RX/TX channel by dir.

The overall steps are:

  1. Execute dma_request_channel() and filter function to find correct eDMA
     RX and TX Channel. If a channel does not exist, fallback to try to
     allocate general memory to memory DMA channel.

  2. Execute dmaengine_slave_config() to configure remote side physical
     address.

  3. Execute dmaengine_prep_slave_single() to create transfer descriptor.

  4. Execute tx_submit().

  5. Execute dma_async_issue_pending()

[bhelgaas: squash in fix from Dan Carpenter <dan.carpenter@oracle.com>:
https://lore.kernel.org/r/Ys2GSTnZhuLzzQG5@kili, also previously posted by
Peng Wu <wupeng58@huawei.com>:
https://lore.kernel.org/all/CANXvt5rK98-cEMgpzopY9POOK8a5=VDib8uKPLgJakOG=hRfwQ@mail.gmail.com/]
Link: https://lore.kernel.org/r/20220524152159.2370739-9-Frank.Li@nxp.com

Signed-off-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Acked-by: Kishon Vijay Abraham I <kishon@ti.com>
Acked-By: Vinod Koul <vkoul@kernel.org>