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diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
index 290a84f..49645277 100644
--- a/arch/arm64/mm/dma-mapping.c
+++ b/arch/arm64/mm/dma-mapping.c

@@ -28,6 +28,7 @@
 #include <linux/dma-contiguous.h>
 #include <linux/vmalloc.h>
 #include <linux/swiotlb.h>
+#include <linux/pci.h>
 
 #include <asm/cacheflush.h>
 

@@ -347,6 +348,16 @@ static int __swiotlb_get_sgtable(struct device *dev, struct sg_table *sgt,
 
 static int __swiotlb_dma_supported(struct device *hwdev, u64 mask)
 {
+#ifdef CONFIG_PCI
+	if (dev_is_pci(hwdev)) {
+		struct pci_dev *pdev = to_pci_dev(hwdev);
+		struct pci_host_bridge *br = pci_find_host_bridge(pdev->bus);
+
+		if (br->dev.dma_mask && (*br->dev.dma_mask) &&
+				(mask & (*br->dev.dma_mask)) != mask)
+			return 0;
+	}
+#endif

Hmm, but this makes it look like the problem is both arm64 and swiotlb
specific, when in reality it's not. Perhaps another hack you could try
would be to register a PCI bus notifier in the host bridge looking for
BUS_NOTIFY_BIND_DRIVER, then you could proxy the DMA ops for each child
device before the driver has probed, but adding a dma_set_mask callback
to limit the mask to what you need?

This is what Renesas BSP tries to do and it does not work.

BUS_NOTIFY_BIND_DRIVER arrives after driver's probe routine exits, but
i/o can be started before that.

Hm. This is strange statement:
 really_probe
 |->driver_sysfs_add
    |-> blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
 					     BUS_NOTIFY_BIND_DRIVER, dev);
...
 |- ret = drv->probe(dev);
...
 |- driver_bound(dev);
    |- blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
					     BUS_NOTIFY_BOUND_DRIVER, dev);

Am I missing smth?

I misinterpreted your message, sorry.

BSP attaches to BUS_NOTIFY_BOUND_DRIVER, not to BUS_NOTIFY_BIND_DRIVER,
and simply overwrites device's dma_mask there.  You are suggesting
something completely different.

I'll check if your approach is practical.


Currently powerpc architecture has one more approach implemented, they
use pci_controller structure provided by host bridge driver, and that
has a set_dma_mask() hook. Maybe extending this beyond powerpc could be
a good idea. However, that will require changing quite a few host bridge
drivers, without any gain for most of those...