Since 9575632052 ("dmaengine: make slave address physical"), the source
and destination addresses of the DMA slave device have been converted to
physical addresses in the CPU address space. It's the DMA device driver's
responsibility to convert them to the DMA bus address space. In case of the
DW eDMA device, the source or destination peripheral (slave) devices reside
in PCI bus space. Thus we need to perform the PCI Host/Endpoint windows-
based (i.e. DT "ranges" property) address translation; otherwise the eDMA
transactions won't work as expected (or can be even harmful) if the CPU and
PCI address spaces don't match.
Note 1: Even though the DMA interleaved template has both source and
destination addresses declared as dma_addr_t, only the CPU memory range
should be mapped to be seen by the DMA device since it's a subject of the
DMA getting towards the system side. The device part must not be mapped
since the slave device resides in the PCI bus space, which isn't affected
by IOMMUs or iATU translations. DW PCIe eDMA generates corresponding
MWr/MRd TLPs on its own.
Note 2: This functionality is mainly required for the remote eDMA setup
since the CPU address must be manually translated into the PCI bus space
before being written to LLI.{SAR,DAR}. If eDMA is embedded in the locally
accessible DW PCIe Root Port/Endpoint, software-based translation isn't
required since hardware will translate it via the Outbound iATU as long as
the DMA_BYPASS flag is cleared. If DMA_BYPASS is set or there is no
Outbound iATU entry that contains the SAR or DAR (for Read and Write
channel respectively), there won't be any translation performed but DMA
will proceed with the corresponding source/destination address as-is.
Link: https://lore.kernel.org/r/20230113171409.30470-8-Sergey.Semin@baikalelectronics.ru
Tested-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Acked-by: Vinod Koul <vkoul@kernel.org>
993d57bbaa