linux-kernel - Re: [RFC PATCH v4 7/8] pwm: Add dummy pwmchip for orphan pwms

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Date:   Tue, 17 Oct 2017 20:05:01 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Brian Norris <briannorris@...omium.org>
Cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jeffy Chen <jeffy.chen@...k-chips.com>,
        lkml <linux-kernel@...r.kernel.org>,
        Heiko Stübner <heiko@...ech.de>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Doug Anderson <dianders@...omium.org>, tfiga@...omium.org,
        seanpaul@...omium.org,
        "linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>
Subject: Re: [RFC PATCH v4 7/8] pwm: Add dummy pwmchip for orphan pwms

On Tue, Oct 17, 2017 at 11:53:01AM -0700, Brian Norris wrote:
> On Tue, Oct 17, 2017 at 07:46:03PM +0100, Mark Brown wrote:

> > I would expect we can get a long way in the DT by doing a pass over the
> > tree and adding links between device nodes in cases where phandle
> > references exist.  There is a potential issue with circular links which
> > I'm just going to handwave away right now but I'd expect that to help
> > otherwise.

> But I didn't think FDTs encoded type info. So you don't really know
> whether a phandle is a phandle -- it's just an int (which happens to
> have a corresponding property in some other node). Are we trusting our
> DT bindings well enough to say that, for example, we know that in any
> given device node, a property like 'pwms' must be a phandle to a PWM
> provider? OK, maybe 'pwms' is a bad example (it's unlikely to get
> reused, and it has a companion '#pwm-cells' property), but grepping the
> DT bindings directory shows a ton of one-off properties that contain
> phandles.

If we're going with the 90% thing we can probably get a long way with a
whitelist of properties, and we'll be able to take that a lot further
with the validatable schemas if they ever happen.

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