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

[Alexander Stein <alexander.stein@xxxxxxxxxxxxxxxxxxxxx>]

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@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
> 
> 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

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