Message-Id: <15A74798-690D-40CA-88F0-A2CA06781546@jcrosoft.com>
Date:	Wed, 14 Jan 2015 00:24:53 +0800
From:	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>
To:	Sascha Hauer <s.hauer@...gutronix.de>
Cc:	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Mark Rutland <mark.rutland@....com>,
	Heiko Stübner <heiko@...ech.de>,
	Catalin Marinas <catalin.marinas@....com>,
	alan.cheng@...iatek.com, Russell King <linux@....linux.org.uk>,
	Hongzhou Yang <hongzhou.yang@...iatek.com>,
	toby.liu@...iatek.com, Grant Likely <grant.likely@...aro.org>,
	"Joe.C" <yingjoe.chen@...iatek.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Vladimir Murzin <vladimir.murzin@....com>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Rob Herring <robh+dt@...nel.org>,
	Matthias Brugger <matthias.bgg@...il.com>,
	dandan.he@...iatek.com, huang eddie <eddie.huang@...iatek.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ashwin Chaugule <ashwin.chaugule@...aro.org>,
	Sascha Hauer <kernel@...gutronix.de>,
	Kumar Gala <galak@...eaurora.org>
Subject: Re: [PATCH v3 2/3] dt-bindings: Add pinctrl bindings for mt65xx/mt81xx.


> On Jan 14, 2015, at 12:16 AM, Sascha Hauer <s.hauer@...gutronix.de> wrote:
> 
> On Tue, Jan 13, 2015 at 11:05:22AM +0100, Linus Walleij wrote:
>>>> I am worried that there is something in your reasoning that sort of
>>>> assumes all pin controllers mux pins one-by-one and not in groups.
>>>> How do we make it impossible to write a device tree that also
>>>> make hardware that do groupwise config viable without ambiguities?
>>> 
>>> Sorry, I don't understand this sentence. What do you mean here?
>>> 
>>> The bindings I suggested are for individual pin based controllers
>>> only. I know there are group based controllers, but I don't want to
>>> change their bindings. I believe there is no single binding that is
>>> good for both types of controllers.
>>> 
>>> I think we must face it that individual pin based controllers are
>>> different from group based controllers. That's the main difference
>>> between different pin controllers and I think there are good reasons
>>> to reflect that in the device tree.
>> 
>> OK let's work on a binding for this usecase.
> 
> Okay.
> 
>> 
>>> You often talk about ambiguities. Could you give an example what
>>> ambiguities you mean?
>> 
>> What happened was this pins = ; arguments were sometimes
>> strings and sometimes integers, that becomes strange to handle
>> in code, ambiguous.
> 
> I see. I like naming it 'pinmux' because that's what it is: pins and
> mux settings. A plain 'pinno' suggests that it contains only pin mubers,
> without mux setting. How about 'pin-no-mux'? We also could add an
> explicit "pins-are-numbered" property instead of distinguishing this
> by property names.
> 
>> 
>> I'm fuzzily referring to the concept of things being named the
>> same way in different device trees, yet lacking commonality,
>> confusing a human reader that they may be the same thing,
>> even if it is possible to write schemas and parsers handling
>> it unambigously, so not ambiguity in the formal logic sense.
>> 
>> If i later want to refactor the code around this to a central
>> parser I cannot do so because it would lead to formal ambiguities
>> and is non-doable.
> 
> There could be a flag in the pinctroller struct indicating whether the
> properties are to be interpreted as strings or as numbers.
> 
>> 
>>> Note that the way we combine pin/mux in a single define is not new,
>>> the i.MX pin controller uses this already and so far I'm not aware of
>>> any problems this makes.
>> 
>> Yeah we never had time to sit down and come up with proper
>> generic pin control bindings, we went with custom bindings
>> partly because of general disagreements, partly because I
>> was new to device tree and honestly had no idea of how
>> to skin this cat.
>> 
>> Now that we get to formalize generic bindings for DT and
>> ACPI and whatever alike, I prefer if we make both groupwise
>> and per-pin pin controllers as strict and well defined as
>> possible.
>> 
>> One minor problem I have with using an integer for mux config
>> is that it assumes something about how many pins, configs etc
>> that may exist on such a system. This should be stated
>> explicitly in the bindings atleast so we know what restrictions
>> we build into them. String-based function+group matching has
>> no such restrictions.
> 
> No problem, that can be documented. Normally the defines should be used
> anyway, not the plain pin numbers.
> 
> BTW one thing I really like about integers is the pure binary size. In
> barebox I also parse the pinmux settings from the device tree. The
> drivers using string matching are multiple times bigger due to the
> string tables:
> 
> -rw-r--r-- 1 sha ptx  5436 Jan 13 15:00 imx-iomux-v3.o
> -rw-r--r-- 1 sha ptx 42060 Jan 13 15:00 pinctrl-tegra30.o

Agreed with Sascha that’s why I chose integer for at91 too

if you want string just use define instead to make it more readable

Best Regards,
J.
> 
> Sascha
> 
> -- 
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