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

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Message-ID: <20140930123933.GA25395@peterchendt>
Date:	Tue, 30 Sep 2014 20:39:34 +0800
From:	Peter Chen <peter.chen@...escale.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	<linux-arm-kernel@...ts.infradead.org>,
	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 Tue, Sep 30, 2014 at 12:03:42PM +0200, Arnd Bergmann wrote:
> On Tuesday 30 September 2014 08:12:07 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;
> > > +     }
> > 
> > My suggestion:
> > 
> > - call dma_coerce_mask_and_coherent(&dev->dev, DMA_BIT_MASK(32)) for both 
> > dt and non-dt
> 
> No, as I explained before, hardcoding the dma mask is always wrong, don't
> do that. Call dma_set_mask_and_coherent and check the return value.
> It's not wrong to do that for both DT and ATAGS.
> 

Thanks, Arnd. I had not thought setting dma mask is so complicated, yes, it
should check the return value, two things to confirm:

- dma_coerce_mask_and_coherent or dma_set_mask_and_coherent, the only difference
of these two API is the first one do "dev->dma_mask = &dev->coherent_dma_mask;"
The reason you suggest choosing dma_set_mask_and_coherent is you do not want
assign dev->dma_mask?
- The second parameter for dma_set_mask_and_coherent is DMA_BIT_MASK(32), is it
ok?

I just a little confused of what's the operation is "hardcoding the dma mask"?

-- 
Best Regards,
Peter Chen
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