Re: [PATCH v6 08/10] dmaengine: tegra: Use iommu-map for stream ID

Frank Li
2026-03-31T14:12:27Z

On Tue, Mar 31, 2026 at 03:53:01PM +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. However, 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@nvidia.com>
> ---
Reviewed-by: Frank Li <Frank.Li@nxp.com>
> drivers/dma/tegra186-gpc-dma.c | 53 ++++++++++++++++++++++++++++------
> 1 file changed, 44 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/dma/tegra186-gpc-dma.c b/drivers/dma/tegra186-gpc-dma.c
> index 9bea2ffb3b9e..cd480d047204 100644
> --- a/drivers/dma/tegra186-gpc-dma.c
> +++ b/drivers/dma/tegra186-gpc-dma.c
> @@ -15,6 +15,7 @@
> #include <linux/module.h>
> #include <linux/of.h>
> #include <linux/of_dma.h>
> +#include <linux/of_device.h>
> #include <linux/platform_device.h>
> #include <linux/reset.h>
> #include <linux/slab.h>
> @@ -1380,9 +1381,13 @@ static int tegra_dma_program_sid(struct tegra_dma_channel *tdc, int stream_id)
> static int tegra_dma_probe(struct platform_device *pdev)
> {
> const struct tegra_dma_chip_data *cdata = NULL;
> + struct tegra_dma_channel *tdc;
> + struct tegra_dma *tdma;
> + struct dma_chan *chan;
> + struct device *chdev;
> + bool use_iommu_map = false;
> unsigned int i;
> u32 stream_id;
> - struct tegra_dma *tdma;
> int ret;
>
> cdata = of_device_get_match_data(&pdev->dev);
> @@ -1410,9 +1415,10 @@ static int tegra_dma_probe(struct platform_device *pdev)
>
> tdma->dma_dev.dev = &pdev->dev;
>
> - if (!tegra_dev_iommu_get_stream_id(&pdev->dev, &stream_id)) {
> - dev_err(&pdev->dev, "Missing iommu stream-id\n");
> - return -EINVAL;
> + use_iommu_map = of_property_present(pdev->dev.of_node, "iommu-map");
> + if (!use_iommu_map) {
> + if (!tegra_dev_iommu_get_stream_id(&pdev->dev, &stream_id))
> + return dev_err_probe(&pdev->dev, -EINVAL, "Missing iommu stream-id\n");
> }
>
> ret = device_property_read_u32(&pdev->dev, "dma-channel-mask",
> @@ -1424,9 +1430,10 @@ static int tegra_dma_probe(struct platform_device *pdev)
> tdma->chan_mask = TEGRA_GPCDMA_DEFAULT_CHANNEL_MASK;
> }
>
> + /* Initialize vchan for each channel and populate the channels list */
> INIT_LIST_HEAD(&tdma->dma_dev.channels);
> for (i = 0; i < cdata->nr_channels; i++) {
> - struct tegra_dma_channel *tdc = &tdma->channels[i];
> + tdc = &tdma->channels[i];
>
> /* Check for channel mask */
> if (!(tdma->chan_mask & BIT(i)))
> @@ -1446,10 +1453,6 @@ static int tegra_dma_probe(struct platform_device *pdev)
>
> vchan_init(&tdc->vc, &tdma->dma_dev);
> tdc->vc.desc_free = tegra_dma_desc_free;
> -
> - /* program stream-id for this channel */
> - tegra_dma_program_sid(tdc, stream_id);
> - tdc->stream_id = stream_id;
> }
>
> dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(cdata->addr_bits));
> @@ -1483,6 +1486,7 @@ static int tegra_dma_probe(struct platform_device *pdev)
> tdma->dma_dev.device_synchronize = tegra_dma_chan_synchronize;
> tdma->dma_dev.residue_granularity = DMA_RESIDUE_GRANULARITY_BURST;
>
> + /* Register the DMA device and the channels */
> ret = dmaenginem_async_device_register(&tdma->dma_dev);
> if (ret < 0) {
> dev_err_probe(&pdev->dev, ret,
> @@ -1490,6 +1494,37 @@ 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)
> + return dev_err_probe(chdev, ret,
> + "Failed to configure IOMMU for channel %d\n", tdc->id);
> +
> + if (!tegra_dev_iommu_get_stream_id(chdev, &stream_id))
> + return dev_err_probe(chdev, -EINVAL,
> + "Failed to get stream ID for channel %d\n", tdc->id);
> +
> + chan->dev->chan_dma_dev = true;
> + }
> +
> + /* program stream-id for this channel */
> + tegra_dma_program_sid(tdc, stream_id);
> + tdc->stream_id = stream_id;
> + }
> +
> ret = devm_of_dma_controller_register(&pdev->dev, pdev->dev.of_node,
> tegra_dma_of_xlate, tdma);
> if (ret < 0) {
> --
> 2.50.1
>