Hi, I've recently had a discussion about the correct way for an SPI driver to handle the num-cs property: https://lkml.org/lkml/2020/8/25/184 Since 8cdcd8aeee281 ("spi: imx/fsl-lpspi: Convert to GPIO descriptors"), the logic of the spi-imx driver is somewhat confusing: If fewer than 3 cs-gpios are defined, and no explicit num-cs property exists, the driver will set num_chipselect to 3 by default, instead of the number of cs-gpios entries. To avoid having to specify num-cs when the number cs-gpios would suffice, I suggested to modify the logic to the following: - If num-cs is set, use that - If num-cs is unset, use the number of cs-gpios - If num-cs is unset and no cs-gpios are defined, use a driver-provided default (which is 3 for spi-imx; this matches the number of native CS pins in older implementations of this SPI controller; i.MX6 and newer support up to 4) Also, would it make sense to add num-cs to all DTS files for boards that actually use fewer than 3 CS pins? At the moment, the num-cs property is not explicitly documented for the spi-imx driver, although the driver understands it. I also suggested to add this to the docs, which Fabio didn't deem a good idea (I don't quite understand the reasoning here - isn't num-cs generally a useful property to have?) Kind regards, Matthias
