linux-kernel - Re: [PATCH] gpio: mcp23s08: Add option to configure pullups.

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Message-ID: <11644726.TmP4uu3h4l@ws-stein>
Date:   Mon, 24 Oct 2016 08:13:54 +0200
From:   Alexander Stein <alexander.stein@...tec-electronic.com>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>
Subject: Re: [PATCH] gpio: mcp23s08: Add option to configure pullups.

On Monday 24 October 2016 02:53:31, Linus Walleij wrote:
> On Fri, Oct 21, 2016 at 5:00 PM, Enric Balletbo i Serra
> 
> <enric.balletbo@...labora.com> wrote:
> > Default is without pullups, but if property is specified in DT and the bit
> > is set, set a pullup on GPIO-n.
> > 
> > Signed-off-by: Enric Balletbo i Serra <enric.balletbo@...labora.com>
> 
> I don't generally like this.
> 
> In device tree it is the consumer that specifies how the line is used,
> not the producer (gpiochip).
> 
> We currently only specify polarity, open drain and open source
> for consumers though.
> 
> And the entire pin control system came into being *exactly* because
> Grant didn't like me adding these things to the GPIO drivers.
> 
> So how many other things does the MCP support? Drive strength?
> Schmitt trigger? Is there a datasheet?

Some unsupported features (AFAIK):
* Input polarity (IPOL register)
* open-drain interrupt pin
* pullup on pins (proposed patch)

Datasheet is here: http://ww1.microchip.com/downloads/en/DeviceDoc/21919e.pdf

Best regards,
Alexander