On Sun, Jun 06, 2021 at 11:36:29AM +0200, Sven Peter 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 using the same logic already present in xhci-plat.c: > First, try to set a coherent dma mask for 64-bit, and then attempt > again with a 32-bit mask if this fails. > > Signed-off-by: Sven Peter <sven@xxxxxxxxxxxxx> > --- > > I have taken the code directly from the xhci-plat.c driver so > I think this change should be fairly low risk. > Unfortunately I only have the Apple M1 to test this on but here > the driver still works with the iommu enabled which limits the > address space to 32 bit. It also enables to use this with the iommu > in bypass mode which requires 64 bit addresses. > > I believe this has been working fine so far since the dwc3 driver > only uses a few very small buffers in host mode which might still > fit within the first 4G of address space on many devices. The > majority of DMA buffers are allocated inside the xhci driver which > will already call dma_set_mask_and_coherent. > > Best, > > Sven > > drivers/usb/dwc3/core.c | 15 +++++++++++++++ > 1 file changed, 15 insertions(+) > > diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c > index b6e53d8212cd..ef6bb6aaffd8 100644 > --- a/drivers/usb/dwc3/core.c > +++ b/drivers/usb/dwc3/core.c > @@ -1545,6 +1545,21 @@ static int dwc3_probe(struct platform_device *pdev) > > dwc3_get_properties(dwc); > > + /* Try to set 64-bit DMA first */ > + if (WARN_ON(!dwc->sysdev->dma_mask)) This will cause systems to reboot if they have panic-on-warn set. Are you sure you want that to happen? I know you copied this from xhci-plat, but let's not duplicate bugs please :) thnaks, greg k-h
