linux-kernel - Re: [PATCH v3 07/12] usb: chipidea: add a usb2 driver for ci13xxx

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Date:	Thu, 17 Jul 2014 13:34:38 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Peter Chen <peter.chen@...escale.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>,
	Antoine Ténart 
	<antoine.tenart@...e-electrons.com>,
	"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 v3 07/12] usb: chipidea: add a usb2 driver for ci13xxx

On Thursday 17 July 2014 19:19:15 Peter Chen wrote:
> 
> Currently, we are designing a generic driver, we don't know what's the
> hardware architecture, we are trying to find a solution how to set
> dma mask for all possible devices which will use this driver, Antoine's
> this patch is trying to cover this feature.
> 
> For example, 
> 
> Marvell Berlin doesn't need to set dma mask specific.
> http://marc.info/?l=linux-arm-kernel&m=140205228507045&w=2
> http://www.spinics.net/lists/linux-usb/msg110598.html
> 
> Xilinx zynq needs to set dma mask as 0xFFFFFFF0
> http://marc.info/?l=linux-usb&m=140384129921706&w=2
> 
> FSL i.mx needs to set dma mask as DMA_BIT_MASK(32)
> https://git.kernel.org/cgit/linux/kernel/git/gregkh/usb.git/tree/drivers/usb/chipidea/ci_hdrc_imx.c?h=usb-next

Ok, I see now. I think we can safely drop it completely then:

- Berlin was only recently added and doesn't need to set the
  mask because the common code handles it just fine now.

- i.mx was added earlier, at a time where it was still necessary

- zynq just made a mistake, 0xFFFFFFF0 was never a valid mask
  and just happened to work by accident.

In summary, the 32-bit default mask will work on all of them,
and we need no special code or DT properties for it.

	Arnd
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