linux-kernel - RE: [PATCH v4 1/4] Documentation: dt-bindings: Describe SROMc configuration

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Date:	Fri, 30 Oct 2015 13:43:07 +0300
From:	Pavel Fedin <p.fedin@...sung.com>
To:	'Krzysztof Kozlowski' <k.kozlowski@...sung.com>,
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:	'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>,
	'Kukjin Kim' <kgene@...nel.org>
Subject: RE: [PATCH v4 1/4] Documentation: dt-bindings: Describe SROMc
 configuration

 Hello!

> Please, carefully look at:
> Documentation/devicetree/bindings/net/gpmc-eth.txt
> Documentation/devicetree/bindings/bus/ti-gpmc.txt
> 
> 1. Try to re-use existing bindings. Although I see existing bank-width
> and gpmc,device-width but yours samsung,srom-data-width seems better.
> Maybe there are other to re-use?

 I've done this and this is what i currently came up with. I'd like to discuss this before respin because nobody needs this
back-and-forth bouncing.
--- cut exynos5410.dtsi ---
		sromc: sromc@...50000 {
			#address-cells = <2>;
			#size-cells = <1>;
			ranges = <0 0 0x04000000 0x20000
				  1 0 0x05000000 0x20000
				  2 0 0x06000000 0x20000
				  3 0 0x07000000 0x20000>;

			compatible = "samsung,exynos-srom";
			reg = <0x12250000 0x14>;
		};
--- cut exynos5410.dtsi ---
--- cut exynos5410-smdk5410.dts ---
&sromc {
	pinctrl-names = "default";
	pinctrl-0 = <&srom_ctl>, <&srom_ebi>;

	ethernet@3 {
		compatible = "smsc,lan9115";
		reg = <3 0 0x10000>;
		phy-mode = "mii";
		interrupt-parent = <&gpx0>;
		interrupts = <5 8>;
		reg-io-width = <2>;
		smsc,irq-push-pull;
		smsc,force-internal-phy;

		samsung,srom-config = <1 9 12 1 9 1 1>;
	};
};
--- cut exynos5410-smdk5410.dts ---

 1. After writing proper ranges i was able to get rid of dedicated bank number property, because now it is the first value in
device's "reg".
 2. I noticed that smsc binding already uses reg-io-width property. I searched for it, and it appears to be reused by many devices.
So, i decided to use it to specify bank width, since it's already there. ti-gpmc uses bank-width because it supports configurations
like reg-io-width = 4 && bank-width = 2. I don't know if it's possible to do the same with SROMc, Exynos doc doesn't tell anything
about 32-bit accesses. But, if you want to support it too, i would suggest the following algorithm:
    if (have bank-width)
        width = bank-width
    else if (have reg-io-width)
        width = reg-io-width
    else
        width = 1 /* default */
 3. About samsung,srom-config array. I have the following reasons to keep if this way:
    - listing every property under own name is just too much typing
    - these values really do not make sense without each other, or partialy. I would say that in array form they are even better
readable, because it is the same order in which they go into the register. However, it is still a nice idea do document them, but...
my PDF has "confidential" watermark on it, and this would mean that i essentially copy some information from it into Linux doc. Is
it okay to do this?
 If you still dislike the array, i'll redo is a set of properties like samsung,srom-tacs, samsung,srom-tcos, etc.

Kind regards,
Pavel Fedin
Expert Engineer
Samsung Electronics Research center Russia

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