linux-kernel - Re: [PATCH v3 1/3] spi: atmel: add support for the internal chip-select of the spi controller

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Message-ID: <yw1xvb771yrl.fsf@unicorn.mansr.com>
Date:	Tue, 05 Jan 2016 21:50:54 +0000
From:	Måns Rullgård <mans@...sr.com>
To:	Cyrille Pitchen <cyrille.pitchen@...el.com>
Cc:	Nicolas Ferre <nicolas.ferre@...el.com>,
	Mark Browk <broonie@...nel.org>, linux-spi@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	devicetree@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>
Subject: Re: [PATCH v3 1/3] spi: atmel: add support for the internal chip-select of the spi controller

Cyrille Pitchen <cyrille.pitchen@...el.com> writes:

> This patch relies on the CSAAT (Chip Select Active After Transfer) feature
> introduced by the version 2 of the spi controller. This new mode allows to
> use properly the internal chip-select output pin of the spi controller
> instead of using external gpios. Consequently, the "cs-gpios" device-tree
> property becomes optional.
>
> When the new CSAAT bit is set into the Chip Select Register, the internal
> chip-select output pin remains asserted till both the following conditions
> become true:
> - the LASTXFER bit is set into the Control Register (or the Transmit Data
>   Register)
> - the Transmit Data Register and its shift register are empty.
>
> WARNING: if the LASTXFER bit is set into the Control Register then new
> data are written into the Transmit Data Register fast enough to keep its
> shifter not empty, the chip-select output pin remains asserted. Only when
> the shifter becomes empty, the chip-select output pin is unasserted.
>
> When the CSAAT bit is clear in the Chip Select Register, the LASTXFER bit
> is ignored in both the Control Register and the Transmit Data Register.
> The internal chip-select output pin remains active as long as the Transmit
> Data Register or its shift register are not empty.
>
> Signed-off-by: Cyrille Pitchen <cyrille.pitchen@...el.com>
> ---
>  drivers/spi/spi-atmel.c | 37 ++++++++++++++++++++++++++++---------
>  1 file changed, 28 insertions(+), 9 deletions(-)

[...]

> @@ -1338,6 +1350,13 @@ static int atmel_spi_probe(struct platform_device *pdev)
>
>  	atmel_get_caps(as);
>
> +	as->use_cs_gpios = true;
> +	if (atmel_spi_is_v2(as) &&
> +	    !of_get_property(pdev->dev.of_node, "cs-gpios", NULL)) {
> +		as->use_cs_gpios = false;
> +		master->num_chipselect = 4;
> +	}

This part breaks the AVR32 boards and probably anything else that
doesn't use devicetree but does use GPIOs for chip select.

-- 
Måns Rullgård
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