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

Akhil R
2026-03-26T11:11:39Z

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@nvidia.com>
---
drivers/dma/tegra186-gpc-dma.c | 59 ++++++++++++++++++++++++++++------
1 file changed, 50 insertions(+), 9 deletions(-)

diff --git a/drivers/dma/tegra186-gpc-dma.c b/drivers/dma/tegra186-gpc-dma.c
index 9bea2ffb3b9e..3b377f34be58 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 +1415,12 @@ 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)) {
+ dev_err(&pdev->dev, "Missing iommu stream-id\n");
+ return -EINVAL;
+ }
}

ret = device_property_read_u32(&pdev->dev, "dma-channel-mask",
@@ -1424,9 +1432,10 @@ 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 +1455,6 @@ 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 +1488,7 @@ 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 +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;
+ }
+
+ 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;
+ }
+
+ 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