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

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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@xxxxxxxxxxxxxxxxxxxx>
> Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx>
> 
> ---
> 
> 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
> 

-- 
மணிவண்ணன் சதாசிவம்



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