linux-kernel - Re: [PATCH 3/4] ARM: tegra: nyan-big: Include compatible revisions for proper detection

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Message-ID: <6501341f-e14c-4876-dcb7-60a33b7621c4@nvidia.com>
Date:   Wed, 21 Sep 2016 08:34:18 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Paul Kocialkowski <contact@...lk.fr>,
        <linux-kernel@...r.kernel.org>
CC:     <devicetree@...r.kernel.org>,
        Stephen Warren <swarren@...dotorg.org>,
        Thierry Reding <thierry.reding@...il.com>,
        <linux-tegra@...r.kernel.org>,
        Alexandre Courbot <gnurou@...il.com>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 3/4] ARM: tegra: nyan-big: Include compatible revisions
 for proper detection


On 20/09/16 19:02, Paul Kocialkowski wrote:
> * PGP Signed by an unknown key
> 
> Le mardi 20 septembre 2016 à 18:56 +0100, Jon Hunter a écrit :
>> On 20/09/16 18:53, Paul Kocialkowski wrote:
>>>
>>>> Old Signed by an unknown key
>>>
>>> Le mardi 20 septembre 2016 à 18:41 +0100, Jon Hunter a écrit :
>>>>
>>>> On 28/08/16 18:32, Paul Kocialkowski wrote:
>>>>>
>>>>>
>>>>> Depthcharge (the payload used with cros devices) will attempt to detect
>>>>> boards using their revision. This includes all the known revisions for
>>>>> the nyan-big board so that the dtb can be selected preferably.
>>>>
>>>> May be I am missing something here, but for the mainline there is only
>>>> one dtb available and so why is this needed for the mainline?
>>>
>>> There is indeed a single dts in mainline, but depthcharge will use the
>>> revision
>>> to match the compatible string (e.g. it will look for google,nyan-big-rev5,
>>> not
>>> google,nyan-big), so we need to list them all in that single dts. Otherwise,
>>> depthcharge will fall back to the default config, which may or may not be
>>> suitable for nyan.
>>
>> Is tegra124-nyan-big.dtb not the default?
> 
> You can't expect that to always be the case. The image format allows many
> different dts to be provided, so I could easily build with multi_v7_defconfig
> and have various dts for various devices in the same image, and just select a
> random one as default.

Really? Sounds odd. I was hoping that tegra124-nyan-big.dtb would be a
catch all.

> Here, default is really a fallback, the right one is expected to be detected by
> this mechanism. And it really doesn't hurt to provide that information for
> proper detection.
> 
> Note that this is done with many other cros devices in mainline (such as rk3288
> veyrons).

Yes, I guess the same is true for the tegra210-smaug and we do define
all the revs for that one. May be extend the changelog comment to say
what may happen without this change and the problem that this is fixing.

Jon	

-- 
nvpublic