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

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Message-ID: <20190502024524.GV14916@sirena.org.uk>
Date:   Thu, 2 May 2019 11:45:24 +0900
From:   Mark Brown <broonie@...nel.org>
To:     Chris Packham <Chris.Packham@...iedtelesis.co.nz>
Cc:     "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        Hamish Martin <Hamish.Martin@...iedtelesis.co.nz>,
        "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "tthayer@...nsource.altera.com" <tthayer@...nsource.altera.com>
Subject: Re: [PATCH 0/3] spi: SPI bus multiplexer

On Sun, Apr 28, 2019 at 10:28:16PM +0000, Chris Packham wrote:

> One other problem that I encounter is the interaction between cs-gpio 
> and SPI_MASTER_GPIO_SS. Having cs-gpio automatically sets SPI_CS_HIGH 
> which has the undesired side-effect that now my real chip select is 
> inverted. I actually wonder if this change breaks commit 8eee6b9dd30d 
> ("spi: Add Flag to Enable Slave Select with GPIO Chip Select.") since 
> now there is an extra inversion on the CS enable.

That sounds like a framework bug which should just be fixed - we
shouldn't be disrupting users of real chip selects when using a GPIO
chip select.  Depending on the hardware we might need a chip select
assigned that isn't connected to anything for use while the GPIOs are
doing the real work but otherwise we shouldn't be breaking things.

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