linux-kernel - Re: [v5 1/2] dt-bindings: gpio: aspeed: Add SGPIO support

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Message-ID: <CACRpkdZcLNe+oM1jWPpva0LECc-P48ab3H-kG7eabMmSvmvioA@mail.gmail.com>
Date:   Mon, 29 Jul 2019 23:57:16 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Andrew Jeffery <andrew@...id.au>
Cc:     Hongwei Zhang <hongweiz@....com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Joel Stanley <joel@....id.au>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        linux-aspeed <linux-aspeed@...ts.ozlabs.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [v5 1/2] dt-bindings: gpio: aspeed: Add SGPIO support

On Mon, Jul 29, 2019 at 2:19 AM Andrew Jeffery <andrew@...id.au> wrote:

> The behaviour is to periodically emit the state of all enabled GPIOs
> (i.e. the ngpios value), one per bus clock cycle. There's no explicit
> addressing scheme, the protocol encodes the value for a given GPIO
> by its position in the data stream relative to a pulse on the "load data"
> (LD) line, whose envelope covers the clock cycle for the last GPIO in
> the sequence. Similar to SPI the bus has both out and in lines, which
> cater to output/input GPIOs.
>
> A rough timing diagram for a 16-GPIO configuration looks like what
> I've pasted here:
>
> https://gist.github.com/amboar/c9543af1957854474b8c05ab357f0675

OK that is complex. I agree we need to keep this driver together.

Yours,
Linus Walleij