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

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Date:	Wed, 1 Oct 2014 06:35:58 +0000
From:	Peter Chen <Peter.Chen@...escale.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Antoine Tenart <antoine.tenart@...e-electrons.com>,
	"thomas.petazzoni@...e-electrons.com" 
	<thomas.petazzoni@...e-electrons.com>,
	"zmxu@...vell.com" <zmxu@...vell.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"balbi@...com" <balbi@...com>,
	"alexandre.belloni@...e-electrons.com" 
	<alexandre.belloni@...e-electrons.com>,
	"p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
	"jszhang@...vell.com" <jszhang@...vell.com>,
	"sebastian.hesselbarth@...il.com" <sebastian.hesselbarth@...il.com>
Subject: RE: [PATCH v6 07/12] usb: chipidea: add a usb2 driver for ci13xxx

 
> Subject: Re: [PATCH v6 07/12] usb: chipidea: add a usb2 driver for ci13xxx
> 
> On Tuesday 30 September 2014 20:39:34 Peter Chen wrote:
> > 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?
> 
> No, that is just the current definition on ARM32 with
> CONFIG_ARCH_MULTIPLATFORM, and that is going to change soon to be DT
> aware.
> dma_set_mask_and_coherent() is supposed to check whether the platform
> can support the respective mask and return an error if it cannot.
> 
> > - 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"?
> 
> dma_coerce_mask_and_coherent() will hardcode the dma mask and override
> whatever the platform says is necessary.
> 

So, we should use dma_set_mask_and_coherent() in most of cases in device driver,
and use dma_coerce_mask_and_coherent() only  when the device's dma_mask is wrong?

Peter

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