linux-kernel - Re: [PATCH v3 4/6] pinctrl: Add pinctrl binding for Broadcom Capri SoCs

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Message-ID: <CACRpkdZ5Cxii48CsVJzEaBhvZOs8JCcR_hJV=RczhHbW4aqG-w@mail.gmail.com>
Date:	Mon, 16 Dec 2013 14:17:29 +0100
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Sherman Yin <syin@...adcom.com>
Cc:	Rob Herring <rob.herring@...xeda.com>,
	Heiko Stübner <heiko@...ech.de>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Stephen Warren <swarren@...dotorg.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Rob Landley <rob@...dley.net>,
	Christian Daudt <bcm@...thebug.org>,
	Russell King <linux@....linux.org.uk>,
	Grant Likely <grant.likely@...aro.org>,
	Matt Porter <matt.porter@...aro.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 4/6] pinctrl: Add pinctrl binding for Broadcom Capri SoCs

On Sat, Dec 14, 2013 at 2:16 AM, Sherman Yin <syin@...adcom.com> wrote:

>>> +- bias-pull-up:                        Integer. Pull up strength in Ohm:
>>> +                                       1: 1.2 kOhm
>>> +                                       2: 1.8 kOhm
>>> +                                       3: 720 Ohm
>>> +                                       4: 2.7 kOhm
>>> +                                       5: 831 Ohm
>>> +                                       6: 1.08 kOhm
>>> +                                       7: 568 Ohm
>>
>>
>> Please do not use these custom enumerators 1 thru 7.
>> Instead say that the argument is given in ohms, so for
>> example:
>>
>> bias-pull-up = <12000>;
>>
>> Then translate this into the proper enumerator in your
>> driver instead.
>
> Ok.  The 3 bits in this enumeration correspond to enabling the 3 pull up Rs
> (1.2k, 1.8k, 2.7k) in parallel, so the enum kind of make sense. But sure I
> can change it to actual ohms and will error out in the driver if specified
> value is not one of the 7.

Aha, that's how they do it :-)

Please write this in a comment in the driver because it makes
it a lot easier to understand what is going on, and e.g. how to
fuzz an apropriate resistance.

Can you tell me something about how such resistors are produced
in silicon?

Yours,
Linus Walleij
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