linux-kernel - Re: [PATCH 1/9] ARM: dts: exynos: Add macros for GPIO configuration

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Date:   Wed, 31 Aug 2016 14:58:41 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Krzysztof Kozlowski <k.kozlowski@...sung.com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Kukjin Kim <kgene@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        devicetree@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Javier Martinez Canillas <javier@....samsung.com>,
        Tomasz Figa <tomasz.figa@...il.com>,
        Sylwester Nawrocki <s.nawrocki@...sung.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [PATCH 1/9] ARM: dts: exynos: Add macros for GPIO configuration

On Wednesday, August 31, 2016 2:53:02 PM CEST Krzysztof Kozlowski wrote:
> On 08/31/2016 02:42 PM, Arnd Bergmann wrote:
> > On Wednesday, August 31, 2016 2:13:25 PM CEST Krzysztof Kozlowski wrote:
> >>
> >> +#define PIN_PULL_NONE          0
> >> +#define PIN_PULL_DOWN          1
> >> +#define PIN_PULL_UP            3
> >> +
> >> +#define PIN_DRV_LV1            0
> >> +#define PIN_DRV_LV2            2
> >> +#define PIN_DRV_LV3            1
> >> +#define PIN_DRV_LV4            3
> >> +
> >> +#define PIN_FUNC_INPUT         0
> >> +#define PIN_FUNC_OUTPUT                1
> >> +#define PIN_FUNC_SPC_2         2
> >> +#define PIN_FUNC_SPC_3         3
> >> +#define PIN_FUNC_SPC_4         4
> >> +#define PIN_FUNC_SPC_5         5
> >> +#define PIN_FUNC_SPC_F         0xf
> > 
> > Any reason for having a copy in each of those files instead of one
> > that is shared across all of them?
> 
> The drive strengths differ between some of them. There are three groups
> of drive strengths:
> 1. Exynos3250, Exynos4 (all) and Exynos5250,
> 2. Exynos5260,
> 3. Exynos5410, 542x and 5800.

I see. That sounds like an even stronger reason to not duplicate
the definitions, as this is very confusing.

> Rest (functions and pull up/down) is the same so sharing the defines is
> possible but not that obvious. Solution would be for example adding a
> SoC-family prefix for PIN_DRV_LVx. Not that good...
> 
> I could put it into three DTSI:
>  - exynos3-pinctrl.dtsi (new file)
>  - exynos5260-pinctrl.dtsi (like it is now)
>  - exynos54xx-pinctrl.dtsi (new file)
> 
> which would reduce the duplication. Other ideas?

I think having the soc-family prefix is better, as it avoids
defining the same symbol to a different value. Better make this
as explicit as possible.

I think overall, a better solution would have been to define the
constants globally (shared with non-exynos) to start with,
and have the driver translate generic numbers into vendor
specific ones. Obviously it's too late for that now.

	Arnd