linux-kernel - Re: [RESEND PATCH 2/4] dt-bindings: add "reduced-width" property for Armada XP SDRAM controller

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Date:   Thu, 10 Aug 2017 21:17:10 +0000
From:   Chris Packham <Chris.Packham@...iedtelesis.co.nz>
To:     Rob Herring <robh@...nel.org>
CC:     "gregory.clement@...e-electrons.com" 
        <gregory.clement@...e-electrons.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "jlu@...gutronix.de" <jlu@...gutronix.de>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [RESEND PATCH 2/4] dt-bindings: add "reduced-width" property for
 Armada XP SDRAM controller

On 11/08/17 08:38, Rob Herring wrote:
> On Mon, Aug 07, 2017 at 01:46:39PM +1200, Chris Packham wrote:
>> Some SoC implementations that use this controller have a reduced pin
>> count so the meaning of "full" and "half" with change.
> 
> s/with/width/ ?
> 

Yes will include in v2.

>>
>> Signed-off-by: Chris Packham <chris.packham@...iedtelesis.co.nz>
>> ---
>>   .../bindings/memory-controllers/mvebu-sdram-controller.txt          | 6 ++++++
>>   1 file changed, 6 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/memory-controllers/mvebu-sdram-controller.txt b/Documentation/devicetree/bindings/memory-controllers/mvebu-sdram-controller.txt
>> index 89657d1d4cd4..3041868321c8 100644
>> --- a/Documentation/devicetree/bindings/memory-controllers/mvebu-sdram-controller.txt
>> +++ b/Documentation/devicetree/bindings/memory-controllers/mvebu-sdram-controller.txt
>> @@ -13,6 +13,12 @@ Required properties:
>>    - reg: a resource specifier for the register space, which should
>>      include all SDRAM controller registers as per the datasheet.
>>   
>> +Optional properties:
>> + - marvell,reduced-width: some SoCs that use this SDRAM controller have
>> +   a reduced pin count. On such systems "full" width is 32-bits and
>> +   "half" width is 16-bits. Set this property to indicate that the SoC
>> +   used is such a system.
> 
> Maybe you should just state what the width is.


Specifying a number like 64/32/16 is done in for some other properties I 
dismissed that because what this is about how we interpret a 
pin-strapping option. I guess "max-width = <64>;" and "max-width = 
<32>"; would achieve the same.


> Or your compatible string should just be specific enough to know the
> width.

I decided against a new compatible sting that because the IP block 
really is the Armada-XP one and the existing compatible string is used 
in other places (using multiple compatible strings would solve that).

I'm not too fussed which of the 3 options are used. Is there any 
particular preference?