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

[Frank Li]

On Mon, Mar 30, 2026 at 11:32:40PM +0530, Akhil R wrote:
> 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@xxxxxxxxxx>
> >> ---
> > ...
> >>
> >> +	/*
> >> +	 * 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.

even that, still can use return dev_err_probe(chddev, -EINVAL, ...) to
short your code.

Frank

>
> Best Regards,
> Akhil