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

[Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>]

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
>