linux-kernel - Re: [PATCH 0/3] spi: SPI bus multiplexer

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Message-ID: <20190412082913.GA6909@sirena.org.uk>
Date:   Fri, 12 Apr 2019 09:29:13 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Chris Packham <chris.packham@...iedtelesis.co.nz>
Cc:     robh+dt@...nel.org, mark.rutland@....com,
        Hamish Martin <hamish.martin@...iedtelesis.co.nz>,
        linux-spi@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] spi: SPI bus multiplexer

On Fri, Apr 12, 2019 at 05:02:10PM +1200, Chris Packham wrote:

> Unfortunately recent changes have stopped my hacks from working. I've
> tried adapting cs-gpios to work with my particular hardware but I came
> to the realisation that the current cs-gpios support assumes a 1:1
> mapping of gpio to SPI device whereas my hardware used the state of the
> gpio selecting the device i.e. a 1:2 mapping.

> This is my attempt to implement a driver to deal with this. One nice
> property is that it is pretty much self contained. The only change to
> the core SPI infrastructure is exposing a function I needed to lookup
> the spi_controller instance.

Why not implement the device that demuxes the GPIOs you're using for
chip select as a GPIO controller?  Presumably it might get used for
things other than chip selects.

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