Re: [PATCH 23/25] dmaengine: dw-edma: Bypass dma-ranges mapping for the local setup

Manivannan Sadhasivam
2022-03-25T19:38:56Z

On Thu, Mar 24, 2022 at 04:48:34AM +0300, Serge Semin wrote:
> DW eDMA doesn't perform any translation of the traffic generated on the
> CPU/Application side. It just generates read/write AXI-bus requests with
> the specified addresses. But in case if the dma-ranges DT-property is
> specified for a platform device node, Linux will use it to map the CPU
> memory regions into the DMAable bus ranges. This isn't what we want for
> the eDMA embedded into the locally accessed DW PCIe Root Port and
> End-point. In order to work that around let's set the chan_dma_dev flag
> for each DW eDMA channel thus forcing the client drivers to getting a
> custom dma-ranges-less parental device for the mappings.
>
> Note it will only work for the client drivers using the
> dmaengine_get_dma_device() method to get the parental DMA device.
>
> Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
> ---
> drivers/dma/dw-edma/dw-edma-core.c | 15 +++++++++++++++
> 1 file changed, 15 insertions(+)
>
> diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
> index 72a51970bfba..ca5cd7c99571 100644
> --- a/drivers/dma/dw-edma/dw-edma-core.c
> +++ b/drivers/dma/dw-edma/dw-edma-core.c
> @@ -716,6 +716,21 @@ static int dw_edma_alloc_chan_resources(struct dma_chan *dchan)
> if (chan->status != EDMA_ST_IDLE)
> return -EBUSY;
>
> + /* Bypass the dma-ranges based memory regions mapping since the
> + * inbound iATU only affects the traffic incoming from the
> + * PCIe bus.
> + */

Bypass the dma-ranges based memory regions mapping since eDMA doesn't do any
address translation for the CPU address?

Other than this,

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

Thanks,
Mani

> + if (chan->dw->chip->flags & DW_EDMA_CHIP_LOCAL) {
> + dchan->dev->chan_dma_dev = true;
> +
> + dchan->dev->device.dma_coherent = chan->dw->chip->dev->dma_coherent;
> + dma_coerce_mask_and_coherent(&dchan->dev->device,
> + dma_get_mask(chan->dw->chip->dev));
> + dchan->dev->device.dma_parms = chan->dw->chip->dev->dma_parms;
> + } else {
> + dchan->dev->chan_dma_dev = false;
> + }
> +
> pm_runtime_get(chan->dw->chip->dev);
>
> return 0;
> --
> 2.35.1
>