Re: [PATCH v6 22/24] dmaengine: dw-edma: Bypass dma-ranges mapping for the local setup

[Serge Semin <fancer.lancer@gmail.com>]

On Tue, Nov 08, 2022 at 12:04:36AM +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 create a
> mapping the PCIe-bus regions into the CPU memory 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.

@Robin, we particularly need you opinion on this patch. I did as you
said: call *_dma_configure() method to initialize the child device and
set the DMA-mask here instead of the platform driver.

@Vinoud, @Manivannan I had to drop your tags from this patch since its
content had been significantly changed.

-Sergey

> 
> Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
> 
> ---
> 
> Changelog v2:
> - Fix the comment a bit to being clearer. (@Manivannan)
> 
> Changelog v3:
> - Conditionally set dchan->dev->device.dma_coherent field since it can
>   be missing on some platforms. (@Manivannan)
> - Remove Manivannan' rb and tb tags since the patch content has been
>   changed.
> 
> Changelog v6:
> - Directly call *_dma_configure() method on the child device used for
>   the DMA buffers mapping. (@Robin)
> - Explicitly set the DMA-mask of the child device in the channel
>   allocation proecedure. (@Robin)
> - Drop @Manivannan and @Vinod rb- and ab-tags due to significant patch
>   content change.
> ---
>  drivers/dma/dw-edma/dw-edma-core.c | 44 ++++++++++++++++++++++++++++++
>  1 file changed, 44 insertions(+)
> 
> diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
> index e3671bfbe186..846518509753 100644
> --- a/drivers/dma/dw-edma/dw-edma-core.c
> +++ b/drivers/dma/dw-edma/dw-edma-core.c
> @@ -6,9 +6,11 @@
>   * Author: Gustavo Pimentel <gustavo.pimentel@synopsys.com>
>   */
>  
> +#include <linux/acpi.h>
>  #include <linux/module.h>
>  #include <linux/device.h>
>  #include <linux/kernel.h>
> +#include <linux/of_device.h>
>  #include <linux/dmaengine.h>
>  #include <linux/err.h>
>  #include <linux/interrupt.h>
> @@ -711,10 +713,52 @@ static irqreturn_t dw_edma_interrupt_common(int irq, void *data)
>  static int dw_edma_alloc_chan_resources(struct dma_chan *dchan)
>  {
>  	struct dw_edma_chan *chan = dchan2dw_edma_chan(dchan);
> +	struct device *dev = chan->dw->chip->dev;
> +	int ret;
>  
>  	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) {
> +		ret = dma_coerce_mask_and_coherent(&dchan->dev->device,
> +						   DMA_BIT_MASK(64));
> +		if (ret) {
> +			ret = dma_coerce_mask_and_coherent(&dchan->dev->device,
> +							   DMA_BIT_MASK(32));
> +			if (ret)
> +				return ret;
> +		}
> +
> +		if (dev_of_node(dev)) {
> +			struct device_node *node = dev_of_node(dev);
> +
> +			ret = of_dma_configure(&dchan->dev->device, node, true);
> +		} else if (has_acpi_companion(dev)) {
> +			struct acpi_device *adev = to_acpi_device_node(dev->fwnode);
> +
> +			ret = acpi_dma_configure(&dchan->dev->device,
> +						 acpi_get_dma_attr(adev));
> +		} else {
> +			ret = -EINVAL;
> +		}
> +
> +		if (ret)
> +			return ret;
> +
> +		if (dchan->dev->device.dma_range_map) {
> +			kfree(dchan->dev->device.dma_range_map);
> +			dchan->dev->device.dma_range_map = NULL;
> +		}
> +
> +		dchan->dev->chan_dma_dev = true;
> +	} else {
> +		dchan->dev->chan_dma_dev = false;
> +	}
> +
>  	return 0;
>  }
>  
> -- 
> 2.38.0
> 
>