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

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Date:	Thu, 25 Sep 2014 09:11:35 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Peter Chen <peter.chen@...escale.com>,
	Antoine Tenart <antoine.tenart@...e-electrons.com>,
	thomas.petazzoni@...e-electrons.com, zmxu@...vell.com,
	devicetree@...r.kernel.org, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, balbi@...com,
	alexandre.belloni@...e-electrons.com, p.zabel@...gutronix.de,
	jszhang@...vell.com, sebastian.hesselbarth@...il.com
Subject: Re: [PATCH v6 07/12] usb: chipidea: add a usb2 driver for ci13xxx

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.

	Arnd
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