linux-kernel - Re: [PATCH RESEND v2 1/4] pinctrl: Update Qualcomm pm8xxx GPIO parameters definitions

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Date:	Thu, 24 Jul 2014 17:23:13 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Linus Walleij <linus.walleij@...aro.org>
CC:	Bjorn Andersson <bjorn.andersson@...ymobile.com>,
	"Ivan T. Ivanov" <iivanov@...sol.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Mark Brown <broonie@...nel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH RESEND v2 1/4] pinctrl: Update Qualcomm pm8xxx GPIO parameters
 definitions

On 07/24/14 08:40, Linus Walleij wrote:
> On Thu, Jul 24, 2014 at 1:47 AM, Stephen Boyd <sboyd@...eaurora.org> wrote:
>
>>> Please add these constants to the table of valid power-source values and use
>>> something like I did to translate them to register values - it makes the DT
>>> much more readable.
>> The DT could be similarly readable if we had a bunch of #defines for the
>> different VIN settings that resolved to the final register value for
>> that pmic. Something like PM8921_GPIO1_14_VPH, PM8921_GPIO19_36_VPH,
>> etc. There would be a lot of them, but then the driver could be really
>> simple and just jam whatever value is in the DT into the register
>> without having to bounce through a mapping table in software to figure
>> out the register value. If we did this for the functions also then I
>> believe we achieve readability without requiring a bunch of drivers for
>> each and every single pmic?
> Not sure but it sounds like you want to make the device tree a jam table,
> (know about individual register offsets, sequences etc). That has been
> throrougly NACKed in the past, because DT is not Open Firmware.
>
> The exception is pinctrl-single which is restricted to single register
> per pin use cases and is still a point of contention...
>

I'm not proposing a jam table. I'm proposing that we make the
function/source property convenient to the driver by having the actual
function field value encoded there instead of some string that has to be
translated through a table in a driver. There's still going to be
shifting and masking of bits in the driver to put the value in the right
place in the register, but we avoid needing N number of drivers for each
pmic just to translate strings into integers (for functions) and
integers into other integers (for the power source). From what I can
tell there isn't any benefit to having the function property be a string
vs. a #define number besides having a human readable string in pinctrl
debugfs. Is there some other benefit?

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
hosted by The Linux Foundation

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