linux-kernel - Re: [PATCH] dt-bindings: i2c: Add armada-38x i2c binding

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Message-ID: <5376f24bf4c540088ce6432097b5cb51@svr-chch-ex1.atlnz.lc>
Date:   Wed, 27 Sep 2017 01:15:12 +0000
From:   Chris Packham <Chris.Packham@...iedtelesis.co.nz>
To:     Gregory CLEMENT <gregory.clement@...e-electrons.com>,
        Kalyan Kinthada <Kalyan.Kinthada@...iedtelesis.co.nz>
CC:     "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "wsa@...-dreams.de" <wsa@...-dreams.de>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "pawel.moll@....com" <pawel.moll@....com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
        "galak@...eaurora.org" <galak@...eaurora.org>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] dt-bindings: i2c: Add armada-38x i2c binding

Hi Gregory,

On 27/09/17 00:56, Gregory CLEMENT wrote:
> Hi Kalyan,
> 
> Please try avoid top-posting.
> 
>   On dim., sept. 24 2017, Kalyan Kinthada <Kalyan.Kinthada@...iedtelesis.co.nz> wrote:
> 
>> Hi Gregory,
>>
>> I got this information from Armada-38x functional errata document.
> 
> OK but in any case just adding a new compatible was not enough you have
> to update the driver in the same time, however for this case we won't
> need it, see below.
> 
>>
>> I can add the "marvell,mv78230-i2c" compatible string to the appropriate  device tree files
>> but the i2c-mv64xxx driver enables an additional  feature (offload i2c transactions)
>> based on the compatible string "marvell,mv78230-i2c".
>>
>> I am not sure if this feature (offload i2c transactions) should be enabled for Armada-38x devices.
>> That is the reason I felt for the need of a new compatible string
>> specifically for Armada-38x SoCs.
> 
> Indeed the Armada-38x SoCs does not support hardware offloading (at
> least according the datasheet). But it happens that in the earlier
> version of the Armada XP the hardware offloading was buggy, so we
> introduced a compatible for this case: marvell,mv78230-a0-i2c. This
> compatible enable the errata fix but not the offloading feature. That
> means that it is exactly the compatible you need for Armada 38x (and
> Armada 39x and 375 I think).

The "mv78230-a0-i2c" dt-binding has the following note

   Note: Only use "marvell,mv78230-a0-i2c" for a
   very rare, initial version of the SoC which
   had broken offload support.  Linux
   auto-detects this and sets it appropriately.

If we are going to re-use this binding for armada-38x we should probably 
remove this note. Personally my preference would be an armada-38x 
compatible string (or 370 if that's the common base of these SoCs). But 
of course we'll go with whatever your preference is as maintainer.

> 
> Gregory
> 
>>
>> Thanks,
>> Kalyan
>> ________________________________________
>> From: Gregory CLEMENT <gregory.clement@...e-electrons.com>
>> Sent: Friday, 22 September 2017 7:30 p.m.
>> To: Kalyan Kinthada
>> Cc: devicetree@...r.kernel.org; wsa@...-dreams.de; robh+dt@...nel.org;
>> pawel.moll@....com; mark.rutland@....com;
>> ijc+devicetree@...lion.org.uk; galak@...eaurora.org;
>> linux-i2c@...r.kernel.org; linux-kernel@...r.kernel.org; Chris Packham
>> Subject: Re: [PATCH] dt-bindings: i2c: Add armada-38x i2c binding
>>
>> Hi Kalyan,
>>
>>   On ven., sept. 22 2017, Kalyan Kinthada <kalyan.kinthada@...iedtelesis.co.nz> wrote:
>>
>>> All armada-38x variants(380, 385, 388) SoCs have an issue
>>> in i2c controller which violates the i2c repeated start timing.
>>
>>
>> Did you had an issue with one of the SoC ?
>> If yes what was your setting ?
>> On my side I never managed to have this sort of issue on Armada 38x.
>>
>>>
>>> This errata is fixed in the i2c-mv64xxx driver but enabled
>>> only for devices with compatible string "marvell,mv78230-i2c".
>>
>> In this case why not just adding the "marvell,mv78230-i2c" as compatible
>> string in the appropriate device tree files ?
>>
>> Gregory
>>
>>>
>>> This patch introduces a new compatible string
>>> "marvell,armada-38x-i2c" for the i2c controller on armada-38x SoCs
>>> so that the workaound is enabled.
>>
>>
>>>
>>> Signed-off-by: Kalyan Kinthada <kalyan.kinthada@...iedtelesis.co.nz>
>>> ---
>>>   Documentation/devicetree/bindings/i2c/i2c-mv64xxx.txt | 1 +
>>>   1 file changed, 1 insertion(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/i2c/i2c-mv64xxx.txt b/Documentation/devicetree/bindings/i2c/i2c-mv64xxx.txt
>>> index 5c30026921..fc100b6bdb 100644
>>> --- a/Documentation/devicetree/bindings/i2c/i2c-mv64xxx.txt
>>> +++ b/Documentation/devicetree/bindings/i2c/i2c-mv64xxx.txt
>>> @@ -14,6 +14,7 @@ Required properties :
>>>                            very rare, initial version of the SoC which
>>>                            had broken offload support.  Linux
>>>                            auto-detects this and sets it appropriately.
>>> +                     - "marvell,armada-38x-i2c"
>>>    - interrupts      : The interrupt number
>>>
>>>   Optional properties :
>>> --
>>> 2.14.1
>>>
>>
>> --
>> Gregory Clement, Free Electrons
>> Kernel, drivers, real-time and embedded Linux
>> development, consulting, training and support.
>> http://free-electrons.com
>