linux-kernel - [RFC PATCH 1/5] spi: use gpio

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Message-Id: <20170525043043.1930-2-chris.packham@alliedtelesis.co.nz>
Date:   Thu, 25 May 2017 16:30:39 +1200
From:   Chris Packham <chris.packham@...iedtelesis.co.nz>
To:     broonie@...nel.org, andy.shevchenko@...il.com,
        linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org,
        rmallon@...il.com, shawnguo@...nel.org
Cc:     linux@...linux.org.uk,
        Chris Packham <chris.packham@...iedtelesis.co.nz>
Subject: [RFC PATCH 1/5] spi: use gpio_desc instead of numeric gpio

By using a gpio_desc and gpiod_set_value() instead of a numeric gpio and
gpio_set_value() the gpio flags are taken into account. This is useful
when using a gpio chip-select to supplement a controllers native
chip-select.

Signed-off-by: Chris Packham <chris.packham@...iedtelesis.co.nz>
---
(I've included this in this series for context, ultimately it should not be
needed once everything is using gpio_desc)

My specific use-case is I have a board that uses the spi-orion driver but
only has one CS pin available. In order to access two spi slave devices the
board has a 1-of-2 decoder/demultiplexer which is driven via a gpio.

The problem is that for one of the 2 slave devices the gpio level required
is opposite to the chip-select so I can't simply specify "spi-cs-high".
With this change I can flag the gpio as active low and the gpio subsystem
takes care of the additional inversion required.

 drivers/spi/spi.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 6f87fec409b5..b39c0f9956dd 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -725,7 +725,10 @@ 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);
+		struct gpio_desc *gpio = gpio_to_desc(spi->cs_gpio);
+
+		if (gpio)
+			gpiod_set_value(gpio, !enable);
 		/* Some SPI masters need both GPIO CS & slave_select */
 		if ((spi->master->flags & SPI_MASTER_GPIO_SS) &&
 		    spi->master->set_cs)
-- 
2.13.0