Re: [PATCH v2] usb: dwc3: support 64 bit DMA in platform driver

[Sven Peter]

On Sun, Jun 6, 2021, at 17:43, Arnd Bergmann wrote:
> On Sun, Jun 6, 2021 at 12:36 PM Sven Peter <sven@xxxxxxxxxxxxx> wrote:
> > diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> > index b6e53d8212cd..4930541a8984 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 (!dwc->sysdev->dma_mask)
> > +               /* Platform did not initialize dma_mask */
> > +               ret = dma_coerce_mask_and_coherent(dwc->sysdev,
> > +                                                  DMA_BIT_MASK(64));
> > +       else
> > +               ret = dma_set_mask_and_coherent(dwc->sysdev, DMA_BIT_MASK(64));
> > +
> > +       /* If seting 64-bit DMA mask fails, fall back to 32-bit DMA mask */
> > +       if (ret) {
> > +               ret = dma_set_mask_and_coherent(dwc->sysdev, DMA_BIT_MASK(32));
> > +               if (ret)
> > +                       return ret;
> > +       }
> 
> Please drop the dma_coerce_mask_and_coherent() code path as well: if
> the device is marked as non-DMA capable in the platform, it's better have
> it not be usable at all than to assume a particular bus property that may
> or may not be present on that bus.
> 
> The 32-bit mask is the default on all buses you might see a dwc3 controller
> on, so you can drop that as well, and just leave the
> dma_set_mask_and_coherent().
> 
>         Arnd
> 

Makes sense, will drop the two things for v3.

Thanks,

Sven