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This works for sysfs, but it prevents per-channel DMA/IOMMU configuration: of_dma_configure() only probes the IOMMU when dev->bus is set, and the IOMMU core only installs probe/release notifiers for buses listed in iommu_buses[]. Drivers that need per-channel IOMMU support currently work around this by assigning dev->bus after device_register(). That leaves the bus subsystem reference count unbalanced because bus_add_device() already ran with a NULL bus, and bus_remove_device() will later drop a reference that was never taken. Add a dedicated bus for DMA channel devices and register it during dmaengine initialisation, before iommu_subsys_init(). The match callback never succeeds, so no driver can bind to these devices. A follow-up patch will register the channel devices on this bus. Signed-off-by: Peng Fan --- drivers/dma/dmaengine.c | 24 +++++++++++++++++++++--- include/linux/dmaengine.h | 4 ++++ 2 files changed, 25 insertions(+), 3 deletions(-) diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c index 34be53487a21d..6fea67f088b35 100644 --- a/drivers/dma/dmaengine.c +++ b/drivers/dma/dmaengine.c @@ -1643,17 +1643,35 @@ void dma_run_dependencies(struct dma_async_tx_descriptor *tx) } EXPORT_SYMBOL_GPL(dma_run_dependencies); +static int dma_chan_bus_match(struct device *dev, + const struct device_driver *drv) +{ + return 0; +} + +const struct bus_type dma_chan_bus_type = { + .name = "dma", + .match = dma_chan_bus_match, +}; + static int __init dma_bus_init(void) { int err = dmaengine_init_unmap_pool(); + if (err) + return err; + + err = bus_register(&dma_chan_bus_type); if (err) return err; err = class_register(&dma_devclass); - if (!err) - dmaengine_debugfs_init(); + if (err) { + bus_unregister(&dma_chan_bus_type); + return err; + } - return err; + dmaengine_debugfs_init(); + return 0; } arch_initcall(dma_bus_init); diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h index 805668fbe4376..14d8f182c7cb5 100644 --- a/include/linux/dmaengine.h +++ b/include/linux/dmaengine.h @@ -412,6 +412,10 @@ struct dma_chan_dev { bool chan_dma_dev; }; +#ifdef CONFIG_DMA_ENGINE +extern const struct bus_type dma_chan_bus_type; +#endif + /** * enum dma_slave_buswidth - defines bus width of the DMA slave * device, source or target buses -- 2.34.1