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

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Date:	Sun, 8 May 2016 13:45:34 +0100
From:	Jon Hunter <jonathanh@...dia.com>
To:	Rob Herring <robh@...nel.org>
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 05/05/16 17:48, Rob Herring wrote:
> 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.

Thanks. Yes if I change the child sizes to be 1, then I guess I need to
have a non-empty ranges anyway.

Cheers
Jon