linux-kernel - Re: [GIT PULL] On-demand device probing

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Message-ID: <20151019160400.GD32054@sirena.org.uk>
Date:	Mon, 19 Oct 2015 17:04:00 +0100
From:	Mark Brown <broonie@...nel.org>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	Rob Herring <robh+dt@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Tomeu Vizoso <tomeu.vizoso@...labora.com>,
	Russell King <linux@....linux.org.uk>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Vinod Koul <vinod.koul@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Alexandre Courbot <gnurou@...il.com>,
	Thierry Reding <thierry.reding@...il.com>,
	David Airlie <airlied@...ux.ie>,
	Terje Bergström <tbergstrom@...dia.com>,
	Stephen Warren <swarren@...dotorg.org>,
	Wolfram Sang <wsa@...-dreams.de>,
	Frank Rowand <frowand.list@...il.com>,
	Grant Likely <grant.likely@...aro.org>,
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Subject: Re: [GIT PULL] On-demand device probing

On Mon, Oct 19, 2015 at 04:29:40PM +0100, David Woodhouse wrote:
> On Mon, 2015-10-19 at 15:50 +0100, Mark Brown wrote:
> > > But the point I'm making is that we are working towards *fixing* that,
> > > and *not* using DT-specific code in places where we should be using the
> > > generic APIs.

> > What is the plan for fixing things here?  It's not obvious (at least to
> > me) that we don't want to have the subsystems having knowledge of how
> > they are bound to a specific firmware which is what you seem to imply
> > here. 

> I don't know that there *is* a coherent plan here to address it all.

> Certainly, we *will* need subsystems to have firmware-specific
> knowledge in some cases. Take GPIO as an example; ACPI *has* a way to
> describe GPIO, and properties which reference GPIO pins are intended to
> work through that — while in DT, properties which reference GPIO pins
> will have different contents. They'll be compatible at the driver
> level, in the sense that there's a call to get a given GPIO given the
> property name, but the subsystems *will* be doing different things
> behind the scenes.

I'd expect that to be the norm rather than the exception.

> > It seems like we're going to have to refactor these bits of code when
> > they get generalised anyway so I'm not sure that the additional cost
> > here is that big.

> That's an acceptable answer — "we're adding legacy code here but we
> know it's going to be refactored anyway". If that's true, all it takes
> is a note in the commit comment to that effect. That's different from
> having not thought about it :)

Given the above I'm not even sure it's legacy code, it's just as likely
we're going to get some parallel ACPI code added to the subsystems for
parsing their bindings.

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