linux-kernel - Re: [PATCH 1/3] dt-bindings: bus: Add documentation for Tegra210 ACONNECT

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Date:	Thu, 5 May 2016 11:48:46 -0500
From:	Rob Herring <robh@...nel.org>
To:	Jon Hunter <jonathanh@...dia.com>
Cc:	Stephen Warren <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Alexandre Courbot <gnurou@...il.com>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH 1/3] dt-bindings: bus: Add documentation for Tegra210 ACONNECT

On Thu, May 5, 2016 at 9:39 AM, Jon Hunter <jonathanh@...dia.com> wrote:
>
> On 03/05/16 19:22, Rob Herring wrote:
>> On Fri, Apr 29, 2016 at 02:53:45PM +0100, Jon Hunter wrote:
>>> Add binding documentation for the Tegra ACONNECT bus that is part of the
>>> Audio Processing Engine (APE) on Tegra210. The ACONNECT bus is used to
>>> access devices within the APE subsystem. The APE is located in a
>>> separate power domain and so accesses made to the ACONNECT require the
>>> power domain to be enabled as well as some platform specific clocks.
>>>
>>> Signed-off-by: Jon Hunter <jonathanh@...dia.com>
>>> ---
>>>  .../bindings/bus/nvidia,tegra210-aconnect.txt      | 45 ++++++++++++++++++++++
>>>  1 file changed, 45 insertions(+)
>>>  create mode 100644 Documentation/devicetree/bindings/bus/nvidia,tegra210-aconnect.txt
>>>
>>> diff --git a/Documentation/devicetree/bindings/bus/nvidia,tegra210-aconnect.txt b/Documentation/devicetree/bindings/bus/nvidia,tegra210-aconnect.txt
>>> new file mode 100644
>>> index 000000000000..e5e915f8fca7
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/bus/nvidia,tegra210-aconnect.txt
>>> @@ -0,0 +1,45 @@
>>> +NVIDIA Tegra ACONNECT Bus
>>> +
>>> +The Tegra ACONNECT bus is an AXI switch which is used to connnect various
>>> +components inside the Audio Processing Engine (APE). All CPU accesses to
>>> +the APE subsystem go through the ACONNECT via an APB to AXI wrapper.
>>> +
>>> +Required properties:
>>> +- compatible: Must be "nvidia,tegra210-aconnect".
>>> +- clocks: Must contain the entries for the APE clock (TEGRA210_CLK_APE),
>>> +  and APE interface clock (TEGRA210_CLK_APB2APE).
>>> +- clock-names: Must contain the names "ape" and "apb2ape" for the corresponding
>>> +  'clocks' entries.
>>> +- power-domains: Must contain a phandle that points to the audio powergate
>>> +  (namely 'aud') for Tegra210.
>>> +- #address-cells: The number of cells used to represent physical base addresses
>>> +  in the host1x address space. Should be 2.
>>> +- #size-cells: The number of cells used to represent the size of an address
>>> +  range in the host1x address space. Should be 2.
>>
>> Do you really need >4GB of child addresses?
>
> Sounds rather silly when you put it like that. No, its not needed. I
> will fix that.
>
>>> +- ranges: 1:1 mapping of the aconnect address space to the CPU address space.
>>
>> Why 1:1 for 256KB of address space?
>
> No good reason. I have looking at what we did for host1x and ahub which
> also have a ranges property and use a 1:1 mapping. For ahub this makes
> sense because it is more of a cross-bar/switch. The aconnect bus is also
> a switch and thought may be that is the easiest thing to do. What is
> recommended here?

Use of non-empty ranges is preferred though there is not much benefit
if the parent and child sizes are the same. However, it does also
limit what is a valid address for those child nodes.

Rob