On Mon, Jun 7, 2021 at 8:18 AM Sven Peter <sven@xxxxxxxxxxxxx> wrote: > > Currently, the dwc3 platform driver does not explicitly ask for > a DMA mask. This makes it fall back to the default 32-bit mask which > breaks the driver on systems that only have RAM starting above the > first 4G like the Apple M1 SoC. > > Fix this by calling dma_set_mask_and_coherent with a 64bit mask. > > Signed-off-by: Sven Peter <sven@xxxxxxxxxxxxx> > --- > > Third time's a charm I hope - this time much simpler :) I think this is almost good, but there is still one small issue: > diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c > index b6e53d8212cd..ba4792b6a98f 100644 > --- a/drivers/usb/dwc3/core.c > +++ b/drivers/usb/dwc3/core.c > @@ -1545,6 +1545,10 @@ static int dwc3_probe(struct platform_device *pdev) > > dwc3_get_properties(dwc); > > + ret = dma_set_mask_and_coherent(dwc->sysdev, DMA_BIT_MASK(64)); > + if (ret) > + return ret; This will now fail on machines with dwc3 connected to a 32-bit bus (or a bus that is accidentally not annotated as supporting 64-bit) when there is some memory that is not addressable through that bus. If dma_set_mask_and_coherent() fails, the platform should just fall back to 32-bit addressing as it did before your change. dma_alloc_*() will do that implicitly by allocating from ZONE_DMA32, while dma_map_*() fails on any non-addressable memory, or falls back to swiotlb if that is available. Arnd