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

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Date:	Fri, 25 Jul 2014 13:29:29 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Stephen Boyd <sboyd@...eaurora.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 Fri, Jul 25, 2014 at 2:23 AM, Stephen Boyd <sboyd@...eaurora.org> wrote:
> 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?

OK I get it ... I think.

One good reason to use strings is that it apart from debugfs makes
for quite readable debug messages if used the right way.

I feel sort of lukewarm on the issue, so I'd let the driver author
decide the most elegant way to deal with this from an end-user
point of view. If it helps people configure and debug their board
set-ups is a crucial factor to me, and I suspect both Ivan and
Björn has some experience with this.

Yours,
Linus Walleij
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