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

[Thierry Reding <thierry.reding@gmail.com>]

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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>
> ---
>  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;

No use in initiazising this since you immediately assign to it the
return value of of_property_present() below.

>  	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");

Looks like checkpatch.pl would complain about this being too long.

>  	}
>  
>  	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);

There are also a few very long lines here. Make sure to run checkpatch
on these patches and remove all warnings. For dev_err_probe() some of
these might be okay. Otherwise, one alternative might be to reduce the
nesting here and push the inner "if" into a separate function.

Thierry

> +
> +			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
> 

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