linux-kernel - Re: [PATCH] spi: Make GPIO CSs honour the SPI_NO

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Date:   Mon, 15 Oct 2018 18:34:18 +0000
From:   Trent Piepho <tpiepho@...inj.com>
To:     "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "phil@...pberrypi.org" <phil@...pberrypi.org>,
        "broonie@...nel.org" <broonie@...nel.org>
Subject: Re: [PATCH] spi: Make GPIO CSs honour the SPI_NO_CS flag

On Fri, 2018-10-12 at 10:23 +0100, Phil Elwell wrote:
> The SPI configuration state includes an SPI_NO_CS flag that disables
> all CS line manipulation, for applications that want to manage their
> own chip selects. However, this flag is ignored by the GPIO CS code
> in the SPI framework.

> @@ -729,7 +729,9 @@ static void spi_set_cs(struct spi_device *spi, bool enable)
>  		enable = !enable;
>  
>  	if (gpio_is_valid(spi->cs_gpio)) {
> -		gpio_set_value(spi->cs_gpio, !enable);
> +		/* Honour the SPI_NO_CS flag */
> +		if (!(spi->mode & SPI_NO_CS))
> +			gpio_set_value(spi->cs_gpio, !enable);
>  		/* Some SPI masters need both GPIO CS & slave_select */
>  		if ((spi->controller->flags & SPI_MASTER_GPIO_SS) &&
>  		    spi->controller->set_cs)

What about the calls to spi->controller->set_cs() after this? Should a
driver provided set_cs method be responsible for checking SPI_NO_CS? 
Or should it not be called in the first place?

I imagine it depends on what set_cs needs to do, which might not be
solely related to changing the CS line.