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

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Date:	Tue, 30 Sep 2014 15:43:40 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Peter Chen <peter.chen@...escale.com>
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 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.

	Arnd
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