linux-kernel - Re: [PATCH v2 0/6] dt-bindings: Convert SP804 to Json-schema (and fix users)

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Message-ID: <28acf821-fa6f-7259-ec1b-4810ca1ff48f@arm.com>
Date:   Fri, 28 Aug 2020 16:44:28 +0100
From:   André Przywara <andre.przywara@....com>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Rob Herring <robh+dt@...nel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Haojian Zhuang <haojian.zhuang@...aro.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Chanho Min <chanho.min@....com>,
        Liviu Dudau <liviu.dudau@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Wei Xu <xuwei5@...ilicon.com>
Subject: Re: [PATCH v2 0/6] dt-bindings: Convert SP804 to Json-schema (and fix
 users)

On 28/08/2020 15:54, Linus Walleij wrote:

Hi,

> On Fri, Aug 28, 2020 at 4:20 PM Andre Przywara <andre.przywara@....com> wrote:
> 
>> This is the second attempt at converting the SP804 timer binding to yaml.
>> Compared to v1, I forbid additional properties, and included the primecell
>> binding. Also the clock-names property is now listed, although without
>> further requirements on the names. Changelog below.
> 
> The series:
> Acked-by: Linus Walleij <linus.walleij@...aro.org>
> 
>> I couldn't test any of those DT files on actual machines, but tried
>> to make the changes in a way that would be transparent to at least the
>> Linux driver. The only other SP804 DT user I could find is FreeBSD,
>> but they seem to use a different binding (no clocks, but a
>> clock-frequency property).
> 
> That's annoying. I suppose FreeBSD just made that up and doesn't
> even have a binding document for it?

I couldn't find bindings at all in their git tree. I don't think they
treat this very formally, it seems to be more use-case driven.
Their SP804 driver does not know how to handle clock properties, so most
of the DTs (in sys/gnu/dts, so apparently copied from Linux) would not
work really well, because the driver assumes a hardcoded frequency of
1MHz by default.
There is only one DT (Annapurna Alpine with Cortex-A15) that provides
this clock-frequency property. The Linux DT does not mention the SP804
in there at all, interestingly.

> In an ideal world I suppose we should go and fix FreeBSD but I have
> no idea how easy or hard that is.

It seems to be messy, at least in this case, and I guess unifying DTs
means some work on drivers as well.
But AFAIK most of the more modern platforms copy the DTs (and thus
implicitly the bindings) from Linux, so there is probably much less
deviation for many more relevant boards.

Cheers,
Andre