linux-kernel - Re: [PATCH v5 05/12] dt: bindings: Add bindings for Marvell Xenon SD Host Controller

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Date:   Fri, 27 Jan 2017 16:36:36 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Gregory CLEMENT <gregory.clement@...e-electrons.com>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Jason Cooper <jason@...edaemon.net>,
        Andrew Lunn <andrew@...n.ch>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Mike Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Ziji Hu <huziji@...vell.com>, Jimmy Xu <zmxu@...vell.com>,
        Jisheng Zhang <jszhang@...vell.com>,
        Nadav Haklai <nadavh@...vell.com>, Ryan Gao <ygao@...vell.com>,
        Doug Jones <dougj@...vell.com>, Victor Gu <xigu@...vell.com>,
        "Wei(SOCP) Liu" <liuw@...vell.com>,
        Wilson Ding <dingwei@...vell.com>,
        Yehuda Yitschak <yehuday@...vell.com>,
        Ma rcin Wojtas <mw@...ihalf.com>,
        Hanna Hawa <hannah@...vell.com>,
        Kostya Porotchkin <kostap@...vell.com>
Subject: Re: [PATCH v5 05/12] dt: bindings: Add bindings for Marvell Xenon SD
 Host Controller

>
> OK, but maybe we could keep the part about the mmcard for the eMMC to
> emphasize that we need to setup this option for the controller.

Right!

>
>>> +
>>> +- no-1-8-v:
>>> +  Select this property when 1.8V signaling voltage supply is unavailable.
>>> +  When this property is enabled, both mmc-ddr-1_8v and mmc-hs400-1_8v should be
>>> +  cleared.
>>
>> Please don't use this sdhci property, unless really needed.
>
> Actually this is a mmc property, at least it is described in this the
> mmc binding:
> Documentation/devicetree/bindings/mmc/mmc.txt

Yes, the documentation is wrong. It should we be moved into the docs for sdhci.

I will send a patch updating it. Apologize for the misleading information.

>
> The description of this optional property is:
> "no-1-8-v: when present, denotes that 1.8v card voltage is not supported on
>   this system, even if the controller claims it is."
>
> So as it is also part of the mmc binding we can remove it from our
> bindings as we are going to do it for the other mmc property.

Nope.

>
> But I am curious to know why do you think we could use it without any
> need. Are you aware of some abuse of this property?

Yes.

>
>>
>> Perhaps you can elaborate exactly why it makes sense for your case. Or
>> perhaps we already discussed this, in either case, please re-fresh my
>> mind.
>
> For instance we need it now on the 7040DB board which does not have the
> 1.8V signal voltage available.

It it's better to describe what the controller/board support, instead
of what it doesn't.

I think you should be able to use other existing mmc DT bindings
(perhaps also you need the brand new "mmc-ddr-3_3v"), instead of the
"no-1-8-v".

Kind regards
Uffe