Re: [PATCH v4 08/10] dmaengine: tegra: Use iommu-map for stream ID

[Frank Li]

On Thu, Mar 26, 2026 at 04:39:45PM +0530, Akhil R wrote:
> Use 'iommu-map', when provided, to get the stream ID to be programmed
> for each channel. Iterate over the channels registered and configure
> each channel device separately using of_dma_configure_id() to allow
> it to use a separate IOMMU domain for the transfer. But do this
> in a second loop since the first loop populates the DMA device channels
> list and async_device_register() registers the channels. Both are
> prerequisites for using the channel device in the next loop.
>
> Channels will continue to use the same global stream ID if the
> 'iommu-map' property is not present in the device tree.
>
> Signed-off-by: Akhil R <akhilrajeev@xxxxxxxxxx>
> ---
...
> @@ -1490,6 +1496,41 @@ static int tegra_dma_probe(struct platform_device *pdev)
>  		return ret;
>  	}
>
> +	/*
> +	 * Configure stream ID for each channel from the channels registered
> +	 * above. This is done in a separate iteration to ensure that only
> +	 * the channels available and registered for the DMA device are used.
> +	 */
> +	list_for_each_entry(chan, &tdma->dma_dev.channels, device_node) {
> +		chdev = &chan->dev->device;
> +		tdc = to_tegra_dma_chan(chan);
> +
> +		if (use_iommu_map) {
> +			chdev->bus = pdev->dev.bus;
> +			dma_coerce_mask_and_coherent(chdev, DMA_BIT_MASK(cdata->addr_bits));
> +
> +			ret = of_dma_configure_id(chdev, pdev->dev.of_node,
> +						  true, &tdc->id);
> +			if (ret) {
> +				dev_err(chdev, "Failed to configure IOMMU for channel %d: %d\n",
> +					tdc->id, ret);
> +				return ret;

This is in probe funciton

	return dev_err_probe();

Frank