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

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Message-ID: <20171003214925.353u7l35jvnergsr@rob-hp-laptop>
Date:   Tue, 3 Oct 2017 16:49:25 -0500
From:   Rob Herring <robh@...nel.org>
To:     Gregory CLEMENT <gregory.clement@...e-electrons.com>
Cc:     Chris Packham <Chris.Packham@...iedtelesis.co.nz>,
        Kalyan Kinthada <Kalyan.Kinthada@...iedtelesis.co.nz>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "wsa@...-dreams.de" <wsa@...-dreams.de>,
        "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

On Wed, Sep 27, 2017 at 09:33:00AM +0200, Gregory CLEMENT wrote:
> Hi Chris,
>  
>  On mer., sept. 27 2017, Chris Packham <Chris.Packham@...iedtelesis.co.nz> wrote:
> 
> > 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
> 
> Updating the documentation is the right thing to do yes.
> 
> 
> > 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.
> 
> If the IP is compatible then there is no reason to add a new one, else
> we will end with a compatible for each SoC and the compatible property
> will just loose its meaning.

If you all had added compatibles for each SoC in the first place, then 
we wouldn't be having this dicussion.

Rob