Re: [PATCH 09/25] dmaengine: dw-edma: Add CPU to PCIe bus address translation

Manivannan Sadhasivam
2022-03-24T17:26:10Z

On Thu, Mar 24, 2022 at 04:48:20AM +0300, Serge Semin wrote:
> Starting from commit 9575632052ba ("dmaengine: make slave address
> physical") the source and destination addresses of the DMA-slave device
> have been converted to being defined in CPU address space. It's DMA-device
> driver responsibility to properly convert them to the reachable DMA bus
> spaces. In case of the DW eDMA device, the source or destination
> peripheral (slave) devices reside PCIe bus space. Thus we need to perform
> the PCIe Host/EP windows-based (i.e. ranges DT-property) addresses
> translation otherwise the eDMA transactions won't work as expected (or can
> be even harmful) in case if the CPU and PCIe address spaces don't match.
>
> Note 1. Even though the DMA interleaved template has both source and
> destination addresses declared of dma_addr_t type only CPU memory range is
> supposed to be mapped in a way so 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 slave device resides in the PCIe 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 PCIe bus space
> before being written to LLI.{SAR,DAR}. If eDMA is embedded into the
> locally accessible DW PCIe RP/EP software-based translation isn't required
> since it will be done by hardware by means of the Outbound iATU as long as
> the DMA_BYPASS flag is cleared. If the later flag is set or there is no
> Outbound iATU entry found to which the SAR or DAR falls in (for Read and
> Write channel respectfully), there won't be any translation performed but
> DMA will proceed with the corresponding source/destination address as is.
>
> Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>

Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

Thanks,
Mani

> ---
> drivers/dma/dw-edma/dw-edma-core.c | 18 +++++++++++++++++-
> include/linux/dma/edma.h | 15 +++++++++++++++
> 2 files changed, 32 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
> index 97743fe44ebf..418b201fef67 100644
> --- a/drivers/dma/dw-edma/dw-edma-core.c
> +++ b/drivers/dma/dw-edma/dw-edma-core.c
> @@ -40,6 +40,17 @@ struct dw_edma_desc *vd2dw_edma_desc(struct virt_dma_desc *vd)
> return container_of(vd, struct dw_edma_desc, vd);
> }
>
> +static inline
> +u64 dw_edma_get_pci_address(struct dw_edma_chan *chan, phys_addr_t cpu_addr)
> +{
> + struct dw_edma_chip *chip = chan->dw->chip;
> +
> + if (chip->ops->pci_address)
> + return chip->ops->pci_address(chip->dev, cpu_addr);
> +
> + return cpu_addr;
> +}
> +
> static struct dw_edma_burst *dw_edma_alloc_burst(struct dw_edma_chunk *chunk)
> {
> struct dw_edma_burst *burst;
> @@ -328,11 +339,11 @@ dw_edma_device_transfer(struct dw_edma_transfer *xfer)
> {
> struct dw_edma_chan *chan = dchan2dw_edma_chan(xfer->dchan);
> enum dma_transfer_direction dir = xfer->direction;
> - phys_addr_t src_addr, dst_addr;
> struct scatterlist *sg = NULL;
> struct dw_edma_chunk *chunk;
> struct dw_edma_burst *burst;
> struct dw_edma_desc *desc;
> + u64 src_addr, dst_addr;
> size_t fsz = 0;
> u32 cnt = 0;
> int i;
> @@ -407,6 +418,11 @@ dw_edma_device_transfer(struct dw_edma_transfer *xfer)
> dst_addr = chan->config.dst_addr;
> }
>
> + if (dir == DMA_DEV_TO_MEM)
> + src_addr = dw_edma_get_pci_address(chan, (phys_addr_t)src_addr);
> + else
> + dst_addr = dw_edma_get_pci_address(chan, (phys_addr_t)dst_addr);
> +
> if (xfer->type == EDMA_XFER_CYCLIC) {
> cnt = xfer->xfer.cyclic.cnt;
> } else if (xfer->type == EDMA_XFER_SCATTER_GATHER) {
> diff --git a/include/linux/dma/edma.h b/include/linux/dma/edma.h
> index 5abac9640a4e..5cc87cfdd685 100644
> --- a/include/linux/dma/edma.h
> +++ b/include/linux/dma/edma.h
> @@ -23,8 +23,23 @@ struct dw_edma_region {
> size_t sz;
> };
>
> +/**
> + * struct dw_edma_core_ops - platform-specific eDMA methods
> + * @irq_vector: Get IRQ number of the passed eDMA channel. Note the
> + * method accepts the channel id in the end-to-end
> + * numbering with the eDMA write channels being placed
> + * first in the row.
> + * @pci_address: Get PCIe bus address corresponding to the passed CPU
> + * address. Note there is no need in specifying this
> + * function if the address translation is performed by
> + * the DW PCIe RP/EP controller with the DW eDMA device in
> + * subject and DMA_BYPASS isn't set for all the outbound
> + * iATU windows. That will be done by the controller
> + * automatically.
> + */
> struct dw_edma_core_ops {
> int (*irq_vector)(struct device *dev, unsigned int nr);
> + u64 (*pci_address)(struct device *dev, phys_addr_t cpu_addr);
> };
>
> enum dw_edma_map_format {
> --
> 2.35.1
>