linux-kernel - Re: [PATCH] spi: lpspi: Add cs-gpio support

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Date:   Tue, 11 Dec 2018 14:26:11 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Clark Wang <xiaoning.wang@....com>
Cc:     "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] spi: lpspi: Add cs-gpio support

On Tue, Dec 04, 2018 at 06:24:59AM +0000, Clark Wang wrote:

> Add cs-gpio feature for LPSPI. Use fsl_lpspi_prepare_message() and
> fsl_lpspi_unprepare_message() to enable and control cs line.
> These two functions will be only called at the beginning and the ending
> of a message transfer.

> Still support using the mode without cs-gpio. It depends on if attribute
> cs-gpio has been configured in dts file.

Why is this not using the core support for GPIO chip selects?  Note that
you can't just implement chip select in the prepare and unprepare,
drivers can toggle chip select within a message so the code should be
looking at the individual transfers to see if cs_change is set and
acting accordingly.

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