Subject: Re: [Patch v3] driver/i2c/mux: Add register-based mux i2c-mux-reg
To: ext York Sun <yorksun@freescale.com>, wsa@the-dreams.de
References: <1434657458-16553-1-git-send-email-yorksun@freescale.com>
Cc: linux-kernel@vger.kernel.org, linux-i2c@vger.kernel.org,
        Paul Bolle <pebolle@tiscali.nl>,
        Peter Korsgaard <peter.korsgaard@barco.com>
From: Alexander Sverdlin <alexander.sverdlin@nokia.com>
Message-ID: <5583B678.6050402@nokia.com>
Date: Fri, 19 Jun 2015 08:28:08 +0200
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Hi!

On 18/06/15 21:57, ext York Sun wrote:
> Based on i2c-mux-gpio driver, similarly the register-based mux
> switch from one bus to another by setting a single register.
> The register can be on PCIe bus, local bus, or any memory-mapped
> address. The endianness of such register can be specified in device
> tree if used, or in platform data.
> 
> Signed-off-by: York Sun <yorksun@freescale.com>
> CC: Wolfram Sang <wsa@the-dreams.de>
> CC: Paul Bolle <pebolle@tiscali.nl>
> CC: Peter Korsgaard <peter.korsgaard@barco.com>
> CC: Alexander Sverdlin <alexander.sverdlin@nokia.com>

I can think about external FPGA applications performing MUX function,
so the code looks useful to me.

Acked-by: Alexander Sverdlin <alexander.sverdlin@nokia.com>

> ---
> According to Alexander's feedback, readback is added. Different sizes
> are supported. I stick with iowrite but adding an option to use iowrite
> big endian in in case needed. Both big- and little-endian are tested.
> Comments are updated.
> 
> Change log:
>   v3: Add support of both big- and little-endian register
>       Add readback after writing to register
>       Add no-read option. By default, readback is alowed.
>       Fix using chan_id transferred back from i2c-mux. It was mistakenly
>         used as an index. It is actually the data to be written.
> 
>   v2: Update to GPLv2+ licence header
>       Use iowrite instead of direct dereference the pointer to write register
>       Add support of difference register size of 1/2/4 bytes
>       Remove i2c_put_adapter(parent) in probe fucntion
>       Replace multiple dev_info() with dev_dbg()
>       Add idle_in_use variable to gate using idle value
>       Add __iomem for register pointer
>       Move platform data header file to include/linux/platform_data/
> 
>  .../devicetree/bindings/i2c/i2c-mux-reg.txt        |   75 +++++
>  drivers/i2c/muxes/Kconfig                          |   11 +
>  drivers/i2c/muxes/Makefile                         |    1 +
>  drivers/i2c/muxes/i2c-mux-reg.c                    |  299 ++++++++++++++++++++
>  include/linux/platform_data/i2c-mux-reg.h          |   44 +++
>  5 files changed, 430 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/i2c/i2c-mux-reg.txt
>  create mode 100644 drivers/i2c/muxes/i2c-mux-reg.c
>  create mode 100644 include/linux/platform_data/i2c-mux-reg.h
> 
> diff --git a/Documentation/devicetree/bindings/i2c/i2c-mux-reg.txt b/Documentation/devicetree/bindings/i2c/i2c-mux-reg.txt
> new file mode 100644
> index 0000000..6e3197f
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/i2c/i2c-mux-reg.txt
> @@ -0,0 +1,75 @@
> +Register-based I2C Bus Mux
> +
> +This binding describes an I2C bus multiplexer that uses a single register
> +to route the I2C signals.
> +
> +Required properties:
> +- compatible: i2c-mux-reg
> +- i2c-parent: The phandle of the I2C bus that this multiplexer's master-side
> +  port is connected to.
> +* Standard I2C mux properties. See mux.txt in this directory.
> +* I2C child bus nodes. See mux.txt in this directory.
> +
> +Optional properties:
> +- reg: this pair of <offset size> specifies the register to control the mux.
> +  The <offset size> depends on its parent node. It can be any memory-mapped
> +  address. The size must be either 1, 2, or 4 bytes. If reg is omitted, the
> +  resource of this device will be used.
> +- little-endian: The existence indicates the register is in little endian.
> +  If omitted, the endianness of the host will be used.
> +- no-read: The existence indicates reading the register is not allowed.
> +- idle-state: value to set the muxer to when idle. When no value is
> +  given, it defaults to the last value used.
> +
> +For each i2c child node, an I2C child bus will be created. They will
> +be numbered based on their order in the device tree.
> +
> +Whenever an access is made to a device on a child bus, the value set
> +in the revelant node's reg property will be output to the register.
> +
> +If an idle state is defined, using the idle-state (optional) property,
> +whenever an access is not being made to a device on a child bus, the
> +register will be set according to the idle value.
> +
> +If an idle state is not defined, the most recently used value will be
> +left programmed into the register.
> +
> +Example of a mux on PCIe card, the host is a powerpc SoC (big endian):
> +
> +	i2c-mux {
> +		/* the <offset size> depends on the address translation
> +		 * of the parent device. If omitted, device resource
> +		 * will be used instead. The size is to determine
> +		 * whether iowrite32, iowrite16, or iowrite8 will be used.
> +		 */
> +		reg = <0x6028 0x4>;
> +		little-endian;		/* little endian register on PCIe */
> +		compatible = "i2c-mux-reg";
> +		#address-cells = <1>;
> +		#size-cells = <0>;
> +		i2c-parent = <&i2c1>;
> +		i2c@0 {
> +			reg = <0>;
> +			#address-cells = <1>;
> +			#size-cells = <0>;
> +
> +			si5338: clock-generator@70 {
> +				compatible = "silabs,si5338";
> +				reg = <0x70>;
> +				/* other stuff */
> +			};
> +		};
> +
> +		i2c@1 {
> +			/* data is written using iowrite32 */
> +			reg = <1>;
> +			#address-cells = <1>;
> +			#size-cells = <0>;
> +
> +			si5338: clock-generator@70 {
> +				compatible = "silabs,si5338";
> +				reg = <0x70>;
> +				/* other stuff */
> +			};
> +		};
> +	};
> diff --git a/drivers/i2c/muxes/Kconfig b/drivers/i2c/muxes/Kconfig
> index f6d313e..77c1257 100644
> --- a/drivers/i2c/muxes/Kconfig
> +++ b/drivers/i2c/muxes/Kconfig
> @@ -29,6 +29,17 @@ config I2C_MUX_GPIO
>  	  This driver can also be built as a module.  If so, the module
>  	  will be called i2c-mux-gpio.
>  
> +config I2C_MUX_REG
> +	tristate "Register-based I2C multiplexer"
> +	help
> +	  If you say yes to this option, support will be included for a
> +	  register based I2C multiplexer. This driver provides access to
> +	  I2C busses connected through a MUX, which is controlled
> +	  by a sinple register.
> +
> +	  This driver can also be built as a module.  If so, the module
> +	  will be called i2c-mux-reg.
> +
>  config I2C_MUX_PCA9541
>  	tristate "NXP PCA9541 I2C Master Selector"
>  	help
> diff --git a/drivers/i2c/muxes/Makefile b/drivers/i2c/muxes/Makefile
> index 465778b..bc517bb 100644
> --- a/drivers/i2c/muxes/Makefile
> +++ b/drivers/i2c/muxes/Makefile
> @@ -4,6 +4,7 @@
>  obj-$(CONFIG_I2C_ARB_GPIO_CHALLENGE)	+= i2c-arb-gpio-challenge.o
>  
>  obj-$(CONFIG_I2C_MUX_GPIO)	+= i2c-mux-gpio.o
> +obj-$(CONFIG_I2C_MUX_REG)	+= i2c-mux-reg.o
>  obj-$(CONFIG_I2C_MUX_PCA9541)	+= i2c-mux-pca9541.o
>  obj-$(CONFIG_I2C_MUX_PCA954x)	+= i2c-mux-pca954x.o
>  obj-$(CONFIG_I2C_MUX_PINCTRL)	+= i2c-mux-pinctrl.o
> diff --git a/drivers/i2c/muxes/i2c-mux-reg.c b/drivers/i2c/muxes/i2c-mux-reg.c
> new file mode 100644
> index 0000000..1692aec
> --- /dev/null
> +++ b/drivers/i2c/muxes/i2c-mux-reg.c
> @@ -0,0 +1,299 @@
> +/*
> + * I2C multiplexer using a single register
> + *
> + * Copyright 2015 Freescale Semiconductor
> + * York Sun  <yorksun@freescale.com>
> + *
> + * 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; either version 2 of the License, or (at your
> + * option) any later version.
> + */
> +
> +#include <linux/i2c.h>
> +#include <linux/i2c-mux.h>
> +#include <linux/init.h>
> +#include <linux/io.h>
> +#include <linux/module.h>
> +#include <linux/of_address.h>
> +#include <linux/platform_data/i2c-mux-reg.h>
> +#include <linux/platform_device.h>
> +#include <linux/slab.h>
> +
> +struct regmux {
> +	struct i2c_adapter *parent;
> +	struct i2c_adapter **adap; /* child busses */
> +	struct i2c_mux_reg_platform_data data;
> +};
> +
> +static int i2c_mux_reg_set(const struct regmux *mux, unsigned int chan_id)
> +{
> +	if (!mux->data.reg)
> +		return -EINVAL;
> +
> +	switch (mux->data.reg_size) {
> +	case 4:
> +		if (mux->data.little_endian) {
> +			iowrite32(chan_id, mux->data.reg);
> +			if (!mux->data.no_read)
> +				ioread32(mux->data.reg);
> +		} else {
> +			iowrite32be(chan_id, mux->data.reg);
> +			if (!mux->data.no_read)
> +				ioread32(mux->data.reg);
> +		}
> +		break;
> +	case 2:
> +		if (mux->data.little_endian) {
> +			iowrite16(chan_id, mux->data.reg);
> +			if (!mux->data.no_read)
> +				ioread16(mux->data.reg);
> +		} else {
> +			iowrite16be(chan_id, mux->data.reg);
> +			if (!mux->data.no_read)
> +				ioread16be(mux->data.reg);
> +		}
> +		break;
> +	case 1:
> +		iowrite8(chan_id, mux->data.reg);
> +		if (!mux->data.no_read)
> +			ioread8(mux->data.reg);
> +		break;
> +	default:
> +		pr_err("Invalid register size\n");
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
> +static int i2c_mux_reg_select(struct i2c_adapter *adap, void *data,
> +			      unsigned int chan)
> +{
> +	struct regmux *mux = data;
> +
> +	return i2c_mux_reg_set(mux, chan);
> +}
> +
> +static int i2c_mux_reg_deselect(struct i2c_adapter *adap, void *data,
> +				unsigned int chan)
> +{
> +	struct regmux *mux = data;
> +
> +	if (mux->data.idle_in_use)
> +		return i2c_mux_reg_set(mux, mux->data.idle);
> +
> +	return 0;
> +}
> +
> +#ifdef CONFIG_OF
> +static int i2c_mux_reg_probe_dt(struct regmux *mux,
> +					struct platform_device *pdev)
> +{
> +	struct device_node *np = pdev->dev.of_node;
> +	struct device_node *adapter_np, *child;
> +	struct i2c_adapter *adapter;
> +	struct resource res;
> +	unsigned *values;
> +	int i = 0;
> +
> +	if (!np)
> +		return -ENODEV;
> +
> +	adapter_np = of_parse_phandle(np, "i2c-parent", 0);
> +	if (!adapter_np) {
> +		dev_err(&pdev->dev, "Cannot parse i2c-parent\n");
> +		return -ENODEV;
> +	}
> +	adapter = of_find_i2c_adapter_by_node(adapter_np);
> +	if (!adapter) {
> +		dev_err(&pdev->dev, "Cannot find parent bus\n");
> +		return -EPROBE_DEFER;
> +	}
> +	mux->parent = adapter;
> +	mux->data.parent = i2c_adapter_id(adapter);
> +	put_device(&adapter->dev);
> +
> +	mux->data.n_values = of_get_child_count(np);
> +	if (of_find_property(np, "little-endian", NULL)) {
> +		mux->data.little_endian = true;
> +	} else {
> +#ifdef __LITTLE_ENDIAN__
> +		mux->data.little_endian = true;
> +#elif defined(__BIG_ENDIAN__)
> +		mux->data.little_endian = false;
> +#else
> +#error Endianness not defined?
> +#endif
> +	}
> +	if (of_find_property(np, "no-read", NULL))
> +		mux->data.no_read = true;
> +	else
> +		mux->data.no_read = false;
> +
> +	values = devm_kzalloc(&pdev->dev,
> +			      sizeof(*mux->data.values) * mux->data.n_values,
> +			      GFP_KERNEL);
> +	if (!values) {
> +		dev_err(&pdev->dev, "Cannot allocate values array");
> +		return -ENOMEM;
> +	}
> +
> +	for_each_child_of_node(np, child) {
> +		of_property_read_u32(child, "reg", values + i);
> +		i++;
> +	}
> +	mux->data.values = values;
> +
> +	if (!of_property_read_u32(np, "idle-state", &mux->data.idle))
> +		mux->data.idle_in_use = true;
> +
> +	/* map address from "reg" if exists */
> +	if (of_address_to_resource(np, 0, &res)) {
> +		mux->data.reg_size = resource_size(&res);
> +		if (mux->data.reg_size > 4) {
> +			dev_err(&pdev->dev, "Invalid address size\n");
> +			return -EINVAL;
> +		}
> +		mux->data.reg = devm_ioremap_resource(&pdev->dev, &res);
> +		if (IS_ERR(mux->data.reg))
> +			return PTR_ERR(mux->data.reg);
> +	}
> +
> +	return 0;
> +}
> +#else
> +static int i2c_mux_reg_probe_dt(struct gpiomux *mux,
> +					struct platform_device *pdev)
> +{
> +	return 0;
> +}
> +#endif
> +
> +static int i2c_mux_reg_probe(struct platform_device *pdev)
> +{
> +	struct regmux *mux;
> +	struct i2c_adapter *parent;
> +	struct resource *res;
> +	int (*deselect)(struct i2c_adapter *, void *, u32);
> +	unsigned int initial_state, class;
> +	int i, ret, nr;
> +
> +	mux = devm_kzalloc(&pdev->dev, sizeof(*mux), GFP_KERNEL);
> +	if (!mux)
> +		return -ENOMEM;
> +
> +	platform_set_drvdata(pdev, mux);
> +
> +	if (dev_get_platdata(&pdev->dev)) {
> +		memcpy(&mux->data, dev_get_platdata(&pdev->dev),
> +			sizeof(mux->data));
> +
> +		parent = i2c_get_adapter(mux->data.parent);
> +		if (!parent) {
> +			dev_err(&pdev->dev, "Parent adapter (%d) not found\n",
> +				mux->data.parent);
> +			return -EPROBE_DEFER;
> +		}
> +		mux->parent = parent;
> +	} else {
> +		ret = i2c_mux_reg_probe_dt(mux, pdev);
> +		if (ret < 0) {
> +			dev_err(&pdev->dev, "Error parsing device tree");
> +			return ret;
> +		}
> +	}
> +
> +	if (!mux->data.reg) {
> +		dev_info(&pdev->dev,
> +			"Register not set, using platform resource\n");
> +		res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +		mux->data.reg_size = resource_size(res);
> +		if (mux->data.reg_size > 4) {
> +			dev_err(&pdev->dev, "Invalid resource size\n");
> +			return -EINVAL;
> +		}
> +		mux->data.reg = devm_ioremap_resource(&pdev->dev, res);
> +		if (IS_ERR(mux->data.reg))
> +			return PTR_ERR(mux->data.reg);
> +	}
> +
> +	mux->adap = devm_kzalloc(&pdev->dev,
> +				 sizeof(*mux->adap) * mux->data.n_values,
> +				 GFP_KERNEL);
> +	if (!mux->adap) {
> +		dev_err(&pdev->dev, "Cannot allocate i2c_adapter structure");
> +		return -ENOMEM;
> +	}
> +
> +	if (mux->data.idle_in_use) {
> +		initial_state = mux->data.idle;
> +		deselect = i2c_mux_reg_deselect;
> +	} else {
> +		initial_state = mux->data.values[0];
> +		deselect = NULL;
> +	}
> +
> +	for (i = 0; i < mux->data.n_values; i++) {
> +		nr = mux->data.base_nr ? (mux->data.base_nr + i) : 0;
> +		class = mux->data.classes ? mux->data.classes[i] : 0;
> +
> +		mux->adap[i] = i2c_add_mux_adapter(mux->parent, &pdev->dev, mux,
> +						   nr, mux->data.values[i],
> +						   class, i2c_mux_reg_select,
> +						   deselect);
> +		if (!mux->adap[i]) {
> +			ret = -ENODEV;
> +			dev_err(&pdev->dev, "Failed to add adapter %d\n", i);
> +			goto add_adapter_failed;
> +		}
> +	}
> +
> +	dev_dbg(&pdev->dev, "%d port mux on %s adapter\n",
> +		 mux->data.n_values, mux->parent->name);
> +
> +	return 0;
> +
> +add_adapter_failed:
> +	for (; i > 0; i--)
> +		i2c_del_mux_adapter(mux->adap[i - 1]);
> +
> +	return ret;
> +}
> +
> +static int i2c_mux_reg_remove(struct platform_device *pdev)
> +{
> +	struct regmux *mux = platform_get_drvdata(pdev);
> +	int i;
> +
> +	for (i = 0; i < mux->data.n_values; i++)
> +		i2c_del_mux_adapter(mux->adap[i]);
> +
> +	i2c_put_adapter(mux->parent);
> +
> +	dev_dbg(&pdev->dev, "Removed\n");
> +
> +	return 0;
> +}
> +
> +static const struct of_device_id i2c_mux_reg_of_match[] = {
> +	{ .compatible = "i2c-mux-reg", },
> +	{},
> +};
> +MODULE_DEVICE_TABLE(of, i2c_mux_reg_of_match);
> +
> +static struct platform_driver i2c_mux_reg_driver = {
> +	.probe	= i2c_mux_reg_probe,
> +	.remove	= i2c_mux_reg_remove,
> +	.driver	= {
> +		.owner	= THIS_MODULE,
> +		.name	= "i2c-mux-reg",
> +	},
> +};
> +
> +module_platform_driver(i2c_mux_reg_driver);
> +
> +MODULE_DESCRIPTION("Register-based I2C multiplexer driver");
> +MODULE_AUTHOR("York Sun <yorksun@freescale.com>");
> +MODULE_LICENSE("GPL");
> +MODULE_ALIAS("platform:i2c-mux-reg");
> diff --git a/include/linux/platform_data/i2c-mux-reg.h b/include/linux/platform_data/i2c-mux-reg.h
> new file mode 100644
> index 0000000..cf0cc1e
> --- /dev/null
> +++ b/include/linux/platform_data/i2c-mux-reg.h
> @@ -0,0 +1,44 @@
> +/*
> + * I2C multiplexer using a single register
> + *
> + * Copyright 2015 Freescale Semiconductor
> + * York Sun <yorksun@freescale.com>
> + *
> + * 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; either version 2 of the License, or (at your
> + * option) any later version.
> + */
> +
> +#ifndef __LINUX_PLATFORM_DATA_I2C_MUX_REG_H
> +#define __LINUX_PLATFORM_DATA_I2C_MUX_REG_H
> +
> +/**
> + * struct i2c_mux_reg_platform_data - Platform-dependent data for i2c-mux-reg
> + * @parent: Parent I2C bus adapter number
> + * @base_nr: Base I2C bus number to number adapters from or zero for dynamic
> + * @values: Array of value for each channel
> + * @n_values: Number of multiplexer channels
> + * @little_endian: Indicating if the register is in little endian
> + * @no_read: Reading the register is not allowed by hardware
> + * @classes: Optional I2C auto-detection classes
> + * @idle: Value to write to mux when idle
> + * @idle_in_use: indicate if idle value is in use
> + * @reg: Virtual address of the register to switch channel
> + * @reg_size: register size in bytes
> + */
> +struct i2c_mux_reg_platform_data {
> +	int parent;
> +	int base_nr;
> +	const unsigned int *values;
> +	int n_values;
> +	bool little_endian;
> +	bool no_read;
> +	const unsigned int *classes;
> +	u32 idle;
> +	bool idle_in_use;
> +	void __iomem *reg;
> +	resource_size_t reg_size;
> +};
> +
> +#endif	/* __LINUX_PLATFORM_DATA_I2C_MUX_REG_H */

-- 
Best regards,
Alexander Sverdlin.
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