On Mon, Jun 7, 2021, at 09:25, Arnd Bergmann wrote: > 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. Makes sense, but just to make sure I understand this correctly: All that needs to be done is call dma_set_mask_and_coherent with a 64 bit mask and then just ignore the return value? Thanks, Sven
