linux-kernel - Re: [PATCH v3 03/15] ACPI: Allow drivers to match using Device Tree compatible property

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Date:	Fri, 3 Oct 2014 10:59:10 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Mark Rutland <mark.rutland@....com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Alexandre Courbot <gnurou@...il.com>,
	Bryan Wu <cooloney@...il.com>,
	Lee Jones <lee.jones@...aro.org>,
	Arnd Bergmann <arnd@...db.de>, Aaron Lu <aaron.lu@...el.com>,
	Darren Hart <dvhart@...ux.intel.com>
Subject: Re: [PATCH v3 03/15] ACPI: Allow drivers to match using Device Tree
 compatible property

On Fri, Oct 03, 2014 at 02:43:03PM +0100, Mark Rutland wrote:
> Hi Rafael,
> 
> On Wed, Oct 01, 2014 at 03:10:40AM +0100, Rafael J. Wysocki wrote:
> > From: Mika Westerberg <mika.westerberg@...ux.intel.com>
> > 
> > We have lots of existing Device Tree enabled drivers and allocating
> > separate _HID for each is not feasible. Instead we allocate special
> > _HID "PRP0001" that means that the match should be done using Device
> > Tree compatible property using driver's .of_match_table instead.
> 
> That's hopefully not the precise meaning of "PRP0001" unless we're
> attempting no semblance of OS independence here?
> 
> I'm still of the opinion that marrying ACPI to existing (and often
> ill-defined) DT bindings is a bad idea. While it's expedient, I believe
> this is going to be a long-term maintenance nightmare.
> 
> I'm very concerned with the prospect of model mismatch between the two
> (e.g. DT clocks properties where ACPI has traditionally been in charge
> of clock management). I've not seen any high-level guidelines w.r.t.
> what should live in _DSD properties and what should not (at least not in
> the ACPI spec itself). There are almost certainly properties that only
> make sense if !ACPI, and likely there will be some that only make sense
> if ACPI.
> 
> So I think that in its current level of standardisation, _DSD only makes
> sense for simple device properties, and not relationships between
> devices, except where ACPI already has some kind of a model (which
> currently seems to cover interrupts and GPIOs). I'd also hope that we
> could expose a 'clean' subset of DT bidnings (i.e. those which aren't
> known to be kept around only for compatibility with legacy DTBs).
> 
> I do not believe it makes sense to share such a low-level interface.
> Given the aforementioned model differences, and the fact that we don't
> need to support _every_ device tree binding, I don't see why this can't
> be handled with separate probe paths in the drivers we care about (as we
> already do for DT vs platform data).

Because as a driver writer I do not want to implement N+1 ways of
getting device configuration. I want one API that works independently of
the underlying platform. The DT vs platform data is bad enough already.

Thanks.

-- 
Dmitry
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