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

From: Mark Brown
Date: Wed May 01 2019 - 22:46:04 EST

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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