Re: [PATCH v2 23/26] dmaengine: dw-edma: Bypass dma-ranges mapping for the local setup

Manivannan Sadhasivam
2022-05-24T13:20:14Z

On Wed, May 04, 2022 at 01:51:01AM +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>
> Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
>
> ---
>
> Changelog v2:
> - Fix the comment a bit to being clearer. (@Manivannan)
> ---
> 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 6a8282eaebaf..908607785401 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 for the eDMA
> + * controlled from the CPU/Application side since in that case
> + * the local memory address is left untranslated.
> + */
> + 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;

I happen to test this series on Qcom ARM32 machine and it errors out during the
compilation due to "dma_coherent" not available on !SWIOTLB ARM32 configs.

Thanks,
Mani

> + 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
>

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