linux-kernel - Re: ARM,SoC: About the use DT-defined properties by 3rd-party drivers

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Message-ID: <57D6AC6F.5040504@tabi.org>
Date:   Mon, 12 Sep 2016 08:23:59 -0500
From:   Timur Tabi <timur@...i.org>
To:     Sebastian Frias <sf84@...oste.net>,
        Mark Rutland <mark.rutland@....com>
Cc:     devicetree <devicetree@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Mason <slash.tmp@...e.fr>
Subject: Re: ARM,SoC: About the use DT-defined properties by 3rd-party drivers

Sebastian Frias wrote:
> 3rd parties could choose to write a driver (as opposed to use say, a user-mode
> library) if it fits their programming model better, if they think they would
> have better performance, or other reasons.
>
> The main idea is to make DT the authoritative source of HW description.

Do you really expect the open-source community to make a serious effort 
to support out-of-tree drivers written by developers who have no 
intention of upstreaming?

There's a process for writing a Linux kernel driver with a DT binding. 
That process is not broken.

>> >Putting smoething together that's only sufficient to support some
>> >out-of-tree driver with implicit assumptions that we are not aware of is
>> >far from fantastic.
> That does not seem very positive and it is not the case anyway, otherwise we
> would not be consulting here:-)

Mark is correct.  Trying to create a device tree binding, and getting it 
correct 100% the first time, without an actual drivers is just 
impossible.  To even attempt that is folly.

> Agreed, right now this whole thing seems like a really hypothetical question,

Yes, it is.

> but the intention is good.

I'm not sure I agree with that.

> Actually, I think it would encourage more SoC manufacturers to use DT as a way
> to document their HW, which is a good thing.

No it isn't.  SOC manufacturers should just release the documentation 
they have.

> But if I understood correctly your comment, you are basically saying that
> without an example is hard to say.
> Since the question seems understood, do you have an example of other SoC's
> doing something similar?

Similar to what?  Every upstream driver today is written the way we're 
talking about -- submit the driver with the binding, and both are 
reviewed together.

> I've seen some big DT descriptions, but it is difficult to know if we are the
> first ones trying to use the DT in this way.

Hopefully, you'll be the last.