Re: [PATCH v6 07/12] usb: chipidea: add a usb2 driver for ci13xxx

Peter Chen
2014-09-26T00:23:53Z

On Thu, Sep 25, 2014 at 09:11:35AM +0200, Arnd Bergmann wrote:
> On Thursday 25 September 2014 09:16:48 Peter Chen wrote:
> > > + }
> > > +
> > > + if (dev->of_node) {
> > > + ret = ci_hdrc_usb2_dt_probe(dev, ci_pdata);
> > > + if (ret)
> > > + goto clk_err;
> > > + } else {
> > > + ret = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32));
> > > + if (ret)
> > > + goto clk_err;
> > > + }
> >
> > Hi Antoine, the above code may not be needed, since get phy and set dma
> > mask are common operation, we can do it at core code, the only thing you
> > need to do is something like: dev->dma_mask = DMA_BIT_MASK(32).
> >
>
> Certainly not, doing that would be broken for a number of reasons:
>
> - dev->dma_mask is a pointer, a driver should not reassign that
> - the device may have been set up for a bus that requires a smaller mask
> that is already set, changing the mask would cause data corruption
> - setting just the dma mask but not coherent mask is wrong
> - setting the dma mask can fail, e.g. if the mask is smaller than the
> smallest memory zone, so you have to check the return value.
>

In current chipidea structure, the parent (glue layer) driver will not be
used for dma, udc/host driver uses dma mask from child (core layer), at core
layer we will do:

pdev->dev.dma_mask = dev->dma_mask; /* this device is parent */
dma_set_coherent_mask(&pdev->dev, dev->coherent_dma_mask);

Would you suggestion us a suitable way? Or it is ok we use just Antoine's way that
call dma_coerce_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32)) at parent
driver no matter dt or non-dt? Thanks.

--
Best Regards,
Peter Chen