Re: [PATCH v5 08/10] dmaengine: tegra: Use iommu-map for stream ID

[Akhil R <akhilrajeev@nvidia.com>]

On Mon, 30 Mar 2026 12:47:24 -0400, Frank Li wrote:
> On Mon, Mar 30, 2026 at 08:14:54PM +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>
>> ---
> ...
>>
>> +	/*
>> +	 * 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", tdc->id);
>> +
>> +			if (!tegra_dev_iommu_get_stream_id(chdev, &stream_id)) {
>> +				dev_err(chdev, "Failed to get stream ID for channel %d\n",
>> +					tdc->id);
>> +				return -EINVAL;
> 
> Can you check similar problem before post patch, here also can use
> 	return dev_err_probe()

I did notice that, but I thought dev_err_probe is to handle -EPROBE_DEFER
and we do not use it when we return a fixed value. It returns -EINVAL here
directly.

Best Regards,
Akhil