i2c: mux: demux-pinctrl: add driver

This driver allows an I2C bus to switch between multiple masters. This
is not hot-switching because connected I2C slaves will be
re-instantiated. It is meant to select the best I2C core at runtime once
the task is known. Example: Prefer i2c-gpio over another I2C core
because of HW errata affecting your use case.
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

Documentation/ABI/testing/sysfs-platform-i2c-demux-pinctrl

+What:		/sys/devices/platform/<i2c-demux-name>/cur_master
+Date:		January 2016
+KernelVersion:	4.6
+Contact:	Wolfram Sang <wsa@the-dreams.de>
+Description:
+
+This file selects the active I2C master for a demultiplexed bus.
+
+Write 0 there for the first master, 1 for the second etc. Reading the file will
+give you a list with the active master marked. Example from a Renesas Lager
+board:
+
+root@Lager:~# cat /sys/devices/platform/i2c@8/cur_master
+* 0 - /i2c@9
+  1 - /i2c@e6520000
+  2 - /i2c@e6530000
+
+root@Lager:~# echo 2 > /sys/devices/platform/i2c@8/cur_master
+
+root@Lager:~# cat /sys/devices/platform/i2c@8/cur_master
+  0 - /i2c@9
+  1 - /i2c@e6520000
+* 2 - /i2c@e6530000

Documentation/devicetree/bindings/i2c/i2c-demux-pinctrl.txt

+Pinctrl-based I2C Bus DeMux
+
+This binding describes an I2C bus demultiplexer that uses pin multiplexing to
+route the I2C signals, and represents the pin multiplexing configuration using
+the pinctrl device tree bindings. This may be used to select one I2C IP core at
+runtime which may have a better feature set for a given task than another I2C
+IP core on the SoC. The most simple example is to fall back to GPIO bitbanging
+if your current runtime configuration hits an errata of the internal IP core.
+
+    +-------------------------------+
+    | SoC                           |
+    |                               |   +-----+  +-----+
+    |   +------------+              |   | dev |  | dev |
+    |   |I2C IP Core1|--\           |   +-----+  +-----+
+    |   +------------+   \-------+  |      |        |
+    |                    |Pinctrl|--|------+--------+
+    |   +------------+   +-------+  |
+    |   |I2C IP Core2|--/           |
+    |   +------------+              |
+    |                               |
+    +-------------------------------+
+
+Required properties:
+- compatible: "i2c-demux-pinctrl"
+- i2c-parent: List of phandles of I2C masters available for selection. The first
+	      one will be used as default.
+- i2c-bus-name: The name of this bus. Also needed as pinctrl-name for the I2C
+		parents.
+
+Furthermore, I2C mux properties and child nodes. See mux.txt in this directory.
+
+Example:
+
+Here is a snipplet for a bus to be demuxed. It contains various i2c clients for
+HDMI, so the bus is named "i2c-hdmi":
+
+	i2chdmi: i2c@8 {
+
+		compatible = "i2c-demux-pinctrl";
+		i2c-parent = <&gpioi2c>, <&iic2>, <&i2c2>;
+		i2c-bus-name = "i2c-hdmi";
+		#address-cells = <1>;
+		#size-cells = <0>;
+
+		ak4643: sound-codec@12 {
+			compatible = "asahi-kasei,ak4643";
+
+			#sound-dai-cells = <0>;
+			reg = <0x12>;
+		};
+
+		composite-in@20 {
+			compatible = "adi,adv7180";
+			reg = <0x20>;
+			remote = <&vin1>;
+
+			port {
+				adv7180: endpoint {
+					bus-width = <8>;
+					remote-endpoint = <&vin1ep0>;
+				};
+			};
+		};
+
+		hdmi@39 {
+			compatible = "adi,adv7511w";
+			reg = <0x39>;
+			interrupt-parent = <&gpio1>;
+			interrupts = <15 IRQ_TYPE_LEVEL_LOW>;
+
+			adi,input-depth = <8>;
+			adi,input-colorspace = "rgb";
+			adi,input-clock = "1x";
+			adi,input-style = <1>;
+			adi,input-justification = "evenly";
+
+			ports {
+				#address-cells = <1>;
+				#size-cells = <0>;
+
+				port@0 {
+					reg = <0>;
+					adv7511_in: endpoint {
+						remote-endpoint = <&du_out_lvds0>;
+					};
+				};
+
+				port@1 {
+					reg = <1>;
+					adv7511_out: endpoint {
+						remote-endpoint = <&hdmi_con>;
+					};
+				};
+			};
+		};
+	};
+
+And for clarification, here are the snipplets for the i2c-parents:
+
+	gpioi2c: i2c@9 {
+		#address-cells = <1>;
+		#size-cells = <0>;
+		compatible = "i2c-gpio";
+		status = "disabled";
+		gpios = <&gpio5 6 GPIO_ACTIVE_HIGH /* sda */
+			 &gpio5 5 GPIO_ACTIVE_HIGH /* scl */
+			>;
+		i2c-gpio,delay-us = <5>;
+	};
+
+...
+
+&i2c2	{
+	pinctrl-0 = <&i2c2_pins>;
+	pinctrl-names = "i2c-hdmi";
+
+	clock-frequency = <100000>;
+};
+
+...
+
+&iic2	{
+	pinctrl-0 = <&iic2_pins>;
+	pinctrl-names = "i2c-hdmi";
+
+	clock-frequency = <100000>;
+};
+
+Please note:
+
+- pinctrl properties for the parent I2C controllers need a pinctrl state
+  with the same name as i2c-bus-name, not "default"!
+
+- the i2c masters must have their status "disabled". This driver will
+  enable them at runtime when needed.

drivers/i2c/muxes/Kconfig

@@ -72,4 +72,13 @@ config I2C_MUX_REG
 	  This driver can also be built as a module.  If so, the module
 	  will be called i2c-mux-reg.
 
+config I2C_DEMUX_PINCTRL
+	tristate "pinctrl-based I2C demultiplexer"
+	depends on PINCTRL && OF
+	select OF_DYNAMIC
+	help
+	  If you say yes to this option, support will be included for an I2C
+	  demultiplexer that uses the pinctrl subsystem. This is useful if you
+	  want to change the I2C master at run-time depending on features.
+
 endmenu

drivers/i2c/muxes/Makefile

@@ -3,6 +3,8 @@
 
 obj-$(CONFIG_I2C_ARB_GPIO_CHALLENGE)	+= i2c-arb-gpio-challenge.o
 
+obj-$(CONFIG_I2C_DEMUX_PINCTRL)		+= i2c-demux-pinctrl.o
+
 obj-$(CONFIG_I2C_MUX_GPIO)	+= i2c-mux-gpio.o
 obj-$(CONFIG_I2C_MUX_PCA9541)	+= i2c-mux-pca9541.o
 obj-$(CONFIG_I2C_MUX_PCA954x)	+= i2c-mux-pca954x.o

drivers/i2c/muxes/i2c-demux-pinctrl.c

+/*
+ * Pinctrl based I2C DeMultiplexer
+ *
+ * Copyright (C) 2015-16 by Wolfram Sang, Sang Engineering <wsa@sang-engineering.com>
+ * Copyright (C) 2015-16 by Renesas Electronics Corporation
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; version 2 of the License.
+ *
+ * See the bindings doc for DTS setup and the sysfs doc for usage information.
+ * (look for filenames containing 'i2c-demux-pinctrl' in Documentation/)
+ */
+
+#include <linux/i2c.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/pinctrl/consumer.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <linux/sysfs.h>
+
+struct i2c_demux_pinctrl_chan {
+	struct device_node *parent_np;
+	struct i2c_adapter *parent_adap;
+	struct of_changeset chgset;
+};
+
+struct i2c_demux_pinctrl_priv {
+	int cur_chan;
+	int num_chan;
+	struct device *dev;
+	const char *bus_name;
+	struct i2c_adapter cur_adap;
+	struct i2c_algorithm algo;
+	struct i2c_demux_pinctrl_chan chan[];
+};
+
+static struct property status_okay = { .name = "status", .length = 3, .value = "ok" };
+
+static int i2c_demux_master_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[], int num)
+{
+	struct i2c_demux_pinctrl_priv *priv = adap->algo_data;
+	struct i2c_adapter *parent = priv->chan[priv->cur_chan].parent_adap;
+
+	return __i2c_transfer(parent, msgs, num);
+}
+
+static u32 i2c_demux_functionality(struct i2c_adapter *adap)
+{
+	struct i2c_demux_pinctrl_priv *priv = adap->algo_data;
+	struct i2c_adapter *parent = priv->chan[priv->cur_chan].parent_adap;
+
+	return parent->algo->functionality(parent);
+}
+
+static int i2c_demux_activate_master(struct i2c_demux_pinctrl_priv *priv, u32 new_chan)
+{
+	struct i2c_adapter *adap;
+	struct pinctrl *p;
+	int ret;
+
+	ret = of_changeset_apply(&priv->chan[new_chan].chgset);
+	if (ret)
+		goto err;
+
+	adap = of_find_i2c_adapter_by_node(priv->chan[new_chan].parent_np);
+	if (!adap) {
+		ret = -ENODEV;
+		goto err;
+	}
+
+	p = devm_pinctrl_get_select(adap->dev.parent, priv->bus_name);
+	if (IS_ERR(p)) {
+		ret = PTR_ERR(p);
+		goto err_with_put;
+	}
+
+	priv->chan[new_chan].parent_adap = adap;
+	priv->cur_chan = new_chan;
+
+	/* Now fill out current adapter structure. cur_chan must be up to date */
+	priv->algo.master_xfer = i2c_demux_master_xfer;
+	priv->algo.functionality = i2c_demux_functionality;
+
+	snprintf(priv->cur_adap.name, sizeof(priv->cur_adap.name),
+		 "i2c-demux (master i2c-%d)", i2c_adapter_id(adap));
+	priv->cur_adap.owner = THIS_MODULE;
+	priv->cur_adap.algo = &priv->algo;
+	priv->cur_adap.algo_data = priv;
+	priv->cur_adap.dev.parent = priv->dev;
+	priv->cur_adap.class = adap->class;
+	priv->cur_adap.retries = adap->retries;
+	priv->cur_adap.timeout = adap->timeout;
+	priv->cur_adap.quirks = adap->quirks;
+	priv->cur_adap.dev.of_node = priv->dev->of_node;
+	ret = i2c_add_adapter(&priv->cur_adap);
+	if (ret < 0)
+		goto err_with_put;
+
+	return 0;
+
+ err_with_put:
+	i2c_put_adapter(adap);
+ err:
+	dev_err(priv->dev, "failed to setup demux-adapter %d (%d)\n", new_chan, ret);
+	return ret;
+}
+
+static int i2c_demux_deactivate_master(struct i2c_demux_pinctrl_priv *priv)
+{
+	int ret, cur = priv->cur_chan;
+
+	if (cur < 0)
+		return 0;
+
+	i2c_del_adapter(&priv->cur_adap);
+	i2c_put_adapter(priv->chan[cur].parent_adap);
+
+	ret = of_changeset_revert(&priv->chan[cur].chgset);
+
+	priv->chan[cur].parent_adap = NULL;
+	priv->cur_chan = -EINVAL;
+
+	return ret;
+}
+
+static int i2c_demux_change_master(struct i2c_demux_pinctrl_priv *priv, u32 new_chan)
+{
+	int ret;
+
+	if (new_chan == priv->cur_chan)
+		return 0;
+
+	ret = i2c_demux_deactivate_master(priv);
+	if (ret)
+		return ret;
+
+	return i2c_demux_activate_master(priv, new_chan);
+}
+
+static ssize_t cur_master_show(struct device *dev, struct device_attribute *attr,
+			   char *buf)
+{
+	struct i2c_demux_pinctrl_priv *priv = dev_get_drvdata(dev);
+	int count = 0, i;
+
+	for (i = 0; i < priv->num_chan && count < PAGE_SIZE; i++)
+		count += scnprintf(buf + count, PAGE_SIZE - count, "%c %d - %s\n",
+				 i == priv->cur_chan ? '*' : ' ', i,
+				 priv->chan[i].parent_np->full_name);
+
+	return count;
+}
+
+static ssize_t cur_master_store(struct device *dev, struct device_attribute *attr,
+			    const char *buf, size_t count)
+{
+	struct i2c_demux_pinctrl_priv *priv = dev_get_drvdata(dev);
+	unsigned int val;
+	int ret;
+
+	ret = kstrtouint(buf, 0, &val);
+	if (ret < 0)
+		return ret;
+
+	if (val >= priv->num_chan)
+		return -EINVAL;
+
+	ret = i2c_demux_change_master(priv, val);
+
+	return ret < 0 ? ret : count;
+}
+static DEVICE_ATTR_RW(cur_master);
+
+static int i2c_demux_pinctrl_probe(struct platform_device *pdev)
+{
+	struct device_node *np = pdev->dev.of_node;
+	struct i2c_demux_pinctrl_priv *priv;
+	int num_chan, i, j, err;
+
+	num_chan = of_count_phandle_with_args(np, "i2c-parent", NULL);
+	if (num_chan < 2) {
+		dev_err(&pdev->dev, "Need at least two I2C masters to switch\n");
+		return -EINVAL;
+	}
+
+	priv = devm_kzalloc(&pdev->dev, sizeof(*priv)
+			   + num_chan * sizeof(struct i2c_demux_pinctrl_chan), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	err = of_property_read_string(np, "i2c-bus-name", &priv->bus_name);
+	if (err)
+		return err;
+
+	for (i = 0; i < num_chan; i++) {
+		struct device_node *adap_np;
+
+		adap_np = of_parse_phandle(np, "i2c-parent", i);
+		if (!adap_np) {
+			dev_err(&pdev->dev, "can't get phandle for parent %d\n", i);
+			err = -ENOENT;
+			goto err_rollback;
+		}
+		priv->chan[i].parent_np = adap_np;
+
+		of_changeset_init(&priv->chan[i].chgset);
+		of_changeset_update_property(&priv->chan[i].chgset, adap_np, &status_okay);
+	}
+
+	priv->num_chan = num_chan;
+	priv->dev = &pdev->dev;
+
+	platform_set_drvdata(pdev, priv);
+
+	/* switch to first parent as active master */
+	i2c_demux_activate_master(priv, 0);
+
+	err = device_create_file(&pdev->dev, &dev_attr_cur_master);
+	if (err)
+		goto err_rollback;
+
+	return 0;
+
+err_rollback:
+	for (j = 0; j < i; j++) {
+		of_node_put(priv->chan[j].parent_np);
+		of_changeset_destroy(&priv->chan[j].chgset);
+	}
+
+	return err;
+}
+
+static int i2c_demux_pinctrl_remove(struct platform_device *pdev)
+{
+	struct i2c_demux_pinctrl_priv *priv = platform_get_drvdata(pdev);
+	int i;
+
+	device_remove_file(&pdev->dev, &dev_attr_cur_master);
+
+	i2c_demux_deactivate_master(priv);
+
+	for (i = 0; i < priv->num_chan; i++) {
+		of_node_put(priv->chan[i].parent_np);
+		of_changeset_destroy(&priv->chan[i].chgset);
+	}
+
+	return 0;
+}
+
+static const struct of_device_id i2c_demux_pinctrl_of_match[] = {
+	{ .compatible = "i2c-demux-pinctrl", },
+	{},
+};
+MODULE_DEVICE_TABLE(of, i2c_demux_pinctrl_of_match);
+
+static struct platform_driver i2c_demux_pinctrl_driver = {
+	.driver	= {
+		.name = "i2c-demux-pinctrl",
+		.of_match_table = i2c_demux_pinctrl_of_match,
+	},
+	.probe	= i2c_demux_pinctrl_probe,
+	.remove	= i2c_demux_pinctrl_remove,
+};
+module_platform_driver(i2c_demux_pinctrl_driver);
+
+MODULE_DESCRIPTION("pinctrl-based I2C demux driver");
+MODULE_AUTHOR("Wolfram Sang <wsa@sang-engineering.com>");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("platform:i2c-demux-pinctrl");