siox: add gpio bus driver

This bus driver uses GPIOs to control the four SIOX bus lines.
Acked-by: Gavin Schenk <g.schenk@eckelmann.de>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/siox/eckelmann,siox-gpio.txt

+Eckelmann SIOX GPIO bus
+
+Required properties:
+- compatible : "eckelmann,siox-gpio"
+- din-gpios, dout-gpios, dclk-gpios, dld-gpios: references gpios for the
+    corresponding bus signals.
+
+Examples:
+
+        siox {
+                compatible = "eckelmann,siox-gpio";
+                pinctrl-names = "default";
+                pinctrl-0 = <&pinctrl_siox>;
+
+                din-gpios = <&gpio6 11 0>;
+                dout-gpios = <&gpio6 8 0>;
+                dclk-gpios = <&gpio6 9 0>;
+                dld-gpios = <&gpio6 10 0>;
+        };

Documentation/devicetree/bindings/vendor-prefixes.txt

@@ -97,6 +97,7 @@ dptechnics	DPTechnics
 dragino	Dragino Technology Co., Limited
 ea	Embedded Artists AB
 ebv	EBV Elektronik
+eckelmann	Eckelmann AG
 edt	Emerging Display Technologies
 eeti	eGalax_eMPIA Technology Inc
 elan	Elan Microelectronic Corp.

drivers/siox/Kconfig

@@ -7,3 +7,12 @@ menuconfig SIOX
 	  to drive additional I/O units.
 
 	  Unless you know better, it is probably safe to say "no" here.
+
+if SIOX
+
+config SIOX_BUS_GPIO
+	tristate "SIOX GPIO bus driver"
+	help
+	  SIOX bus driver that controls the four bus lines using GPIOs.
+
+endif

drivers/siox/Makefile

 obj-$(CONFIG_SIOX) += siox-core.o
+obj-$(CONFIG_SIOX_BUS_GPIO) += siox-bus-gpio.o

drivers/siox/siox-bus-gpio.c

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2015-2017 Pengutronix, Uwe Kleine-König <kernel@pengutronix.de>
+ */
+
+#include <linux/gpio/consumer.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+
+#include <linux/delay.h>
+
+#include "siox.h"
+
+#define DRIVER_NAME "siox-gpio"
+
+struct siox_gpio_ddata {
+	struct gpio_desc *din;
+	struct gpio_desc *dout;
+	struct gpio_desc *dclk;
+	struct gpio_desc *dld;
+};
+
+static unsigned int siox_clkhigh_ns = 1000;
+static unsigned int siox_loadhigh_ns;
+static unsigned int siox_bytegap_ns;
+
+static int siox_gpio_pushpull(struct siox_master *smaster,
+			      size_t setbuf_len, const u8 setbuf[],
+			      size_t getbuf_len, u8 getbuf[])
+{
+	struct siox_gpio_ddata *ddata = siox_master_get_devdata(smaster);
+	size_t i;
+	size_t cycles = max(setbuf_len, getbuf_len);
+
+	/* reset data and clock */
+	gpiod_set_value_cansleep(ddata->dout, 0);
+	gpiod_set_value_cansleep(ddata->dclk, 0);
+
+	gpiod_set_value_cansleep(ddata->dld, 1);
+	ndelay(siox_loadhigh_ns);
+	gpiod_set_value_cansleep(ddata->dld, 0);
+
+	for (i = 0; i < cycles; ++i) {
+		u8 set = 0, get = 0;
+		size_t j;
+
+		if (i >= cycles - setbuf_len)
+			set = setbuf[i - (cycles - setbuf_len)];
+
+		for (j = 0; j < 8; ++j) {
+			get <<= 1;
+			if (gpiod_get_value_cansleep(ddata->din))
+				get |= 1;
+
+			/* DOUT is logically inverted */
+			gpiod_set_value_cansleep(ddata->dout, !(set & 0x80));
+			set <<= 1;
+
+			gpiod_set_value_cansleep(ddata->dclk, 1);
+			ndelay(siox_clkhigh_ns);
+			gpiod_set_value_cansleep(ddata->dclk, 0);
+		}
+
+		if (i < getbuf_len)
+			getbuf[i] = get;
+
+		ndelay(siox_bytegap_ns);
+	}
+
+	gpiod_set_value_cansleep(ddata->dld, 1);
+	ndelay(siox_loadhigh_ns);
+	gpiod_set_value_cansleep(ddata->dld, 0);
+
+	/*
+	 * Resetting dout isn't necessary protocol wise, but it makes the
+	 * signals more pretty because the dout level is deterministic between
+	 * cycles. Note that this only affects dout between the master and the
+	 * first siox device. dout for the later devices depend on the output of
+	 * the previous siox device.
+	 */
+	gpiod_set_value_cansleep(ddata->dout, 0);
+
+	return 0;
+}
+
+static int siox_gpio_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct siox_gpio_ddata *ddata;
+	int ret;
+	struct siox_master *smaster;
+
+	smaster = siox_master_alloc(&pdev->dev, sizeof(*ddata));
+	if (!smaster) {
+		dev_err(dev, "failed to allocate siox master\n");
+		return -ENOMEM;
+	}
+
+	platform_set_drvdata(pdev, smaster);
+	ddata = siox_master_get_devdata(smaster);
+
+	ddata->din = devm_gpiod_get(dev, "din", GPIOD_IN);
+	if (IS_ERR(ddata->din)) {
+		ret = PTR_ERR(ddata->din);
+		dev_err(dev, "Failed to get %s GPIO: %d\n", "din", ret);
+		goto err;
+	}
+
+	ddata->dout = devm_gpiod_get(dev, "dout", GPIOD_OUT_LOW);
+	if (IS_ERR(ddata->dout)) {
+		ret = PTR_ERR(ddata->dout);
+		dev_err(dev, "Failed to get %s GPIO: %d\n", "dout", ret);
+		goto err;
+	}
+
+	ddata->dclk = devm_gpiod_get(dev, "dclk", GPIOD_OUT_LOW);
+	if (IS_ERR(ddata->dclk)) {
+		ret = PTR_ERR(ddata->dclk);
+		dev_err(dev, "Failed to get %s GPIO: %d\n", "dclk", ret);
+		goto err;
+	}
+
+	ddata->dld = devm_gpiod_get(dev, "dld", GPIOD_OUT_LOW);
+	if (IS_ERR(ddata->dld)) {
+		ret = PTR_ERR(ddata->dld);
+		dev_err(dev, "Failed to get %s GPIO: %d\n", "dld", ret);
+		goto err;
+	}
+
+	smaster->pushpull = siox_gpio_pushpull;
+	/* XXX: determine automatically like spi does */
+	smaster->busno = 0;
+
+	ret = siox_master_register(smaster);
+	if (ret) {
+		dev_err(dev, "Failed to register siox master: %d\n", ret);
+err:
+		siox_master_put(smaster);
+	}
+
+	return ret;
+}
+
+static int siox_gpio_remove(struct platform_device *pdev)
+{
+	struct siox_master *master = platform_get_drvdata(pdev);
+
+	siox_master_unregister(master);
+
+	return 0;
+}
+
+static const struct of_device_id siox_gpio_dt_ids[] = {
+	{ .compatible = "eckelmann,siox-gpio", },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, siox_gpio_dt_ids);
+
+static struct platform_driver siox_gpio_driver = {
+	.probe = siox_gpio_probe,
+	.remove = siox_gpio_remove,
+
+	.driver = {
+		.name = DRIVER_NAME,
+		.of_match_table = siox_gpio_dt_ids,
+	},
+};
+module_platform_driver(siox_gpio_driver);
+
+MODULE_AUTHOR("Uwe Kleine-Koenig <u.kleine-koenig@pengutronix.de>");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("platform:" DRIVER_NAME);