linux-kernel - RE: [PATCH v5 10/10] arm: dts: genmai: Add ethernet pin group

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Message-ID: <SG2PR06MB11650F50D93653212039A4348A130@SG2PR06MB1165.apcprd06.prod.outlook.com>
Date:   Fri, 28 Apr 2017 14:48:52 +0000
From:   Chris Brandt <Chris.Brandt@...esas.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
CC:     Jacopo Mondi <jacopo+renesas@...ndi.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v5 10/10] arm: dts: genmai: Add ethernet pin group

Hi Geert,

On Friday, April 28, 2017, Geert Uytterhoeven wrote:
> >> Shouldn't the interrupt (connected to P1_15) be described?
> >
> > That interrupt pin from the PHY is not used. It did not need to be
> connected.
> 
> But it is connected, according to the schematics.

P1_15 can be configured as:
 * GPIO_IN
 * AN7
 * AVB_CAPTURE

So...I guess you would 'describe' it as an GPIO-input.

> DT describes hardware, not software limitations.

Describing things is fine, but the kernel code takes the DT and then start configuring things based on it.

For example, on the RSK board, that line is connected to P4_14. P4_14 can be configured as IRQ6...but IRQ6 comes out in 8 different pin choices, and I might want to use one of those other choices, so I don't want to describe P4_14 as an interrupt.

If it was just describing that "pin 15 of the PHY chip is tied to pin Y19 of the RZ/A1H", that's fine because it's hardware connection that's not going to change.
But...the DT also defines the pin muxing...which is a software decision (do I want to get interrupt or just manually poll or simple ignore it).
This is the part of the whole "DT is for hardware description only" that doesn't really make sense to me.

Chris