Re: [PATCH v1 2/2] arm: dts: mt2701: add nor flash node

From: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
To: Boris Brezillon <boris.brezillon@free-electrons.com>
Cc: Marek Vasut <marek.vasut@gmail.com>,
	Rob Herring <robh+dt@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	devicetree@vger.kernel.org,
	Guochun Mao <guochun.mao@mediatek.com>,
	Richard Weinberger <richard@nod.at>,
	Russell King <linux@armlinux.org.uk>,
	linux-kernel@vger.kernel.org, linux-mtd@lists.infradead.org,
	Matthias Brugger <matthias.bgg@gmail.com>,
	linux-mediatek@lists.infradead.org,
	Cyrille Pitchen <cyrille.pitchen@atmel.com>,
	Brian Norris <computersforpeace@gmail.com>,
	David Woodhouse <dwmw2@infradead.org>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v1 2/2] arm: dts: mt2701: add nor flash node
Date: Tue, 17 Jan 2017 14:36:50 +1100	[thread overview]
Message-ID: <20170117143650.5db87148@free-electrons.com> (raw)
In-Reply-To: <20170116094032.6f471f11@bbrezillon>

Hello,

(Side note: you guys should learn about stripping irrelevant parts of
an e-mail when replying!)

On Mon, 16 Jan 2017 09:40:32 +0100, Boris Brezillon wrote:

> > Well this is OK I guess, but then you can also use "mediatek,mt8173-nor"
> > as the oldest supported compatible and be done with it, no ? It looks a
> > bit crappy though, I admit that ...
> 
> Let's stop bikeshedding and wait for DT maintainers feedback
> before taking a decision ;-).
> 
> Rob, Mark, any opinion?

I agree that a clarification would be good. There are really two
options:

 1. Have two compatible strings in the DT, the one that matches the
    exact SoC where the IP is found (first compatible string) and the
    one that matches some other SoC where the same IP is found (second
    compatible string). Originally, Linux only supports the second
    compatible string in its device driver, but if it happens that a
    difference is found between two IPs that we thought were the same,
    we can add support for the first compatible string in the driver,
    with a slightly different behavior.

 2. Have a single compatible string in the DT, matching the exact SoC
    where the IP is found. This involves adding immediately this
    compatible string in the corresponding driver.

I've not really been able to figure out which of the two options is the
most future-proof/appropriate.

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com