linux-kernel - Re: [PATCH 1/2] [v4] net: emac: emac gigabit ethernet controller driver

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Message-ID: <CAL_Jsq+1ssgBHERNyBNhz=SDC5j20xjE8PWM5JCgWSvHCnGQyw@mail.gmail.com>
Date:	Fri, 15 Apr 2016 10:59:07 -0500
From:	Rob Herring <robh+dt@...nel.org>
To:	Timur Tabi <timur@...eaurora.org>
Cc:	Vikram Sethi <vikrams@...eaurora.org>,
	Florian Fainelli <f.fainelli@...il.com>,
	netdev <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	linux-arm-msm <linux-arm-msm@...r.kernel.org>,
	Sagar Dharia <sdharia@...eaurora.org>,
	Shanker Donthineni <shankerd@...eaurora.org>,
	Greg Kroah-Hartman <greg@...ah.com>,
	Christopher Covington <cov@...eaurora.org>,
	Gilad Avidov <gavidov@...eaurora.org>,
	Andrew Lunn <andrew@...n.ch>,
	Bjorn Andersson <bjorn.andersson@...aro.org>,
	Mark Langsdorf <mlangsdo@...hat.com>,
	Jon Masters <jcm@...hat.com>,
	Andy Gross <agross@...eaurora.org>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH 1/2] [v4] net: emac: emac gigabit ethernet controller driver

On Fri, Apr 15, 2016 at 10:44 AM, Timur Tabi <timur@...eaurora.org> wrote:
> Rob Herring wrote:
>>>
>>> >
>>> >         dma-mask = <0 0xffffffff>;
>>> >
>>> >or
>>> >
>>> >         dma-mask = <0xffffffff 0xffffffff>;
>>
>> No. See dma-ranges.
>
>
> How exactly should I use dma-ranges?  I can't find any other drivers that
> queries that property and uses the result to call dma_set_mask.  I thought
> the dma-ranges property is intended to specify address translation.  I don't
> need to translate any address, I just need to know a single number.

You may only care about the size, but the binding has to handle the
more complex case. Here's an example

<0x0 0x2 0x0 0x1 0x0>

dma address 0 (cell 0) maps to cpu (parent) address 0x2_00000000 (cell
1-2) and the range/size is 4G (cell 3-4).

If you have the same base address, then use the same address. The core
will calculate the mask based on the size. IIRC, we also handle ~0 as
a special case to support 4G for #size-cell=1.

Rob