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

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Date:	Thu, 17 Jul 2014 12:21:56 +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 01:20:54 Peter Chen wrote:
> Thanks, arnd.
> 
> For chipidea generic glue layer case, if there are three devices who use this
> driver, and all devices have 32-bit bus, some devices have less 32 address lines.
> For example:
> 
> - the device_a doesn't need to use dma_mask
> - the device_b needs dma_mask as 0xfffffffff
> - the device_c needs dma_mask as 0xfffffff0, assume it has only 28 address lines

This makes no sense. You always need a dma mask, so the first case doesn't exist,
and the second one is the default.

In the third case, I assume you mean 0x0fffffff, which is a 28-bit mask.

> My questions are:
> - Can we not set dma_mask at driver, and only set dma-ranges at dts for device_b
> and device_c as a solution to cover this different dma mask use case?

try to understand my earlier reply. What is the problem with device_b?
Is that a limitation of the bus it is connected to, or the version of the
chipidea hardware?

> - If we can't use this solution, would you suggest one?

It depends on what the requirement of the hardware is, as I explained
now for three times.

> - If we can use this solution, for device_b and device_c, how can we write dma-ranges?
> I can't find any arm platforms use it, only some powerpc platform use it.
> According to the definition from Power_ePAPR_APPROVED_v1.1.pdf, it is
> dma-ranges = <child-bus-address, parent-bus-address, length>
> but I find the powerpc has different way for using dma-ranges. 

It's now handled by of_dma_configure() in drivers/of/platform.c for all
architectures.

	Arnd
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