Date:   Mon, 28 Aug 2017 10:01:45 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Danilo Krummrich <danilokrummrich@...develop.de>
Cc:     linux-kernel@...r.kernel.org, linux-input@...r.kernel.org,
        linus.walleij@...aro.org, rdunlap@...radead.org,
        devicetree@...r.kernel.org, robh@...nel.org
Subject: Re: [PATCH v9 1/2] serio: PS/2 gpio bit banging driver for serio bus

On Mon, Aug 21, 2017 at 09:31:41PM +0200, Danilo Krummrich wrote:
> This driver provides PS/2 serio bus support by implementing bit banging
> with the GPIO API. The GPIO pins, data and clock, can be configured with
> a node in the device tree or by generic device properties (GDP).
> 
> Writing to a device is supported as well, though it is possible timings
> can not be halt as they are tough and difficult to reach with bit banging.
> Therefore it can be configured (also in DT and GDP) whether the serio
> write function should be available for clients.
> 
> This driver is for development purposes and not recommended for productive
> use. However, this driver can be useful e.g. when no USB port is available
> or using old peripherals is desired as PS/2 controller chips getting rare.
> 
> This driver was tested on bcm2825 and on Kirin 960 and it worked well
> together with the atkbd and psmouse driver.
> 
> Signed-off-by: Danilo Krummrich <danilokrummrich@...develop.de>

Applied, thank you.

> ---
>  Documentation/gpio/drivers-on-gpio.txt |   5 +
>  drivers/input/serio/Kconfig            |  11 +
>  drivers/input/serio/Makefile           |   1 +
>  drivers/input/serio/ps2-gpio.c         | 453 +++++++++++++++++++++++++++++++++
>  4 files changed, 470 insertions(+)
>  create mode 100644 drivers/input/serio/ps2-gpio.c
> 
> diff --git a/Documentation/gpio/drivers-on-gpio.txt b/Documentation/gpio/drivers-on-gpio.txt
> index 306513251713..9a78d385b92e 100644
> --- a/Documentation/gpio/drivers-on-gpio.txt
> +++ b/Documentation/gpio/drivers-on-gpio.txt
> @@ -84,6 +84,11 @@ hardware descriptions such as device tree or ACPI:
>    NAND flash MTD subsystem and provides chip access and partition parsing like
>    any other NAND driving hardware.
>  
> +- ps2-gpio: drivers/input/serio/ps2-gpio.c is used to drive a PS/2 (IBM) serio
> +  bus, data and clock line, by bit banging two GPIO lines. It will appear as
> +  any other serio bus to the system and makes it possible to connect drivers
> +  for e.g. keyboards and other PS/2 protocol based devices.
> +
>  Apart from this there are special GPIO drivers in subsystems like MMC/SD to
>  read card detect and write protect GPIO lines, and in the TTY serial subsystem
>  to emulate MCTRL (modem control) signals CTS/RTS by using two GPIO lines. The
> diff --git a/drivers/input/serio/Kconfig b/drivers/input/serio/Kconfig
> index c3d05b4d3118..21488c048fa3 100644
> --- a/drivers/input/serio/Kconfig
> +++ b/drivers/input/serio/Kconfig
> @@ -292,6 +292,17 @@ config SERIO_SUN4I_PS2
>  	  To compile this driver as a module, choose M here: the
>  	  module will be called sun4i-ps2.
>  
> +config SERIO_GPIO_PS2
> +	tristate "GPIO PS/2 bit banging driver"
> +	depends on GPIOLIB
> +	help
> +	  Say Y here if you want PS/2 bit banging support via GPIO.
> +
> +	  To compile this driver as a module, choose M here: the
> +	  module will be called ps2-gpio.
> +
> +	  If you are unsure, say N.
> +
>  config USERIO
>  	tristate "User space serio port driver support"
>  	help
> diff --git a/drivers/input/serio/Makefile b/drivers/input/serio/Makefile
> index 2374ef9b33d7..767bd9b6e1ed 100644
> --- a/drivers/input/serio/Makefile
> +++ b/drivers/input/serio/Makefile
> @@ -30,4 +30,5 @@ obj-$(CONFIG_SERIO_APBPS2)	+= apbps2.o
>  obj-$(CONFIG_SERIO_OLPC_APSP)	+= olpc_apsp.o
>  obj-$(CONFIG_HYPERV_KEYBOARD)	+= hyperv-keyboard.o
>  obj-$(CONFIG_SERIO_SUN4I_PS2)	+= sun4i-ps2.o
> +obj-$(CONFIG_SERIO_GPIO_PS2)	+= ps2-gpio.o
>  obj-$(CONFIG_USERIO)		+= userio.o
> diff --git a/drivers/input/serio/ps2-gpio.c b/drivers/input/serio/ps2-gpio.c
> new file mode 100644
> index 000000000000..b50e3817f3c4
> --- /dev/null
> +++ b/drivers/input/serio/ps2-gpio.c
> @@ -0,0 +1,453 @@
> +/*
> + * GPIO based serio bus driver for bit banging the PS/2 protocol
> + *
> + * Author: Danilo Krummrich <danilokrummrich@...develop.de>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + */
> +
> +#include <linux/gpio/consumer.h>
> +#include <linux/interrupt.h>
> +#include <linux/module.h>
> +#include <linux/serio.h>
> +#include <linux/slab.h>
> +#include <linux/platform_device.h>
> +#include <linux/workqueue.h>
> +#include <linux/completion.h>
> +#include <linux/mutex.h>
> +#include <linux/preempt.h>
> +#include <linux/property.h>
> +#include <linux/of.h>
> +#include <linux/jiffies.h>
> +#include <linux/delay.h>
> +
> +#define DRIVER_NAME		"ps2-gpio"
> +
> +#define PS2_MODE_RX		0
> +#define PS2_MODE_TX		1
> +
> +#define PS2_START_BIT		0
> +#define PS2_DATA_BIT0		1
> +#define PS2_DATA_BIT1		2
> +#define PS2_DATA_BIT2		3
> +#define PS2_DATA_BIT3		4
> +#define PS2_DATA_BIT4		5
> +#define PS2_DATA_BIT5		6
> +#define PS2_DATA_BIT6		7
> +#define PS2_DATA_BIT7		8
> +#define PS2_PARITY_BIT		9
> +#define PS2_STOP_BIT		10
> +#define PS2_TX_TIMEOUT		11
> +#define PS2_ACK_BIT		12
> +
> +#define PS2_DEV_RET_ACK		0xfa
> +#define PS2_DEV_RET_NACK	0xfe
> +
> +#define PS2_CMD_RESEND		0xfe
> +
> +struct ps2_gpio_data {
> +	struct device *dev;
> +	struct serio *serio;
> +	unsigned char mode;
> +	struct gpio_desc *gpio_clk;
> +	struct gpio_desc *gpio_data;
> +	bool write_enable;
> +	int irq;
> +	unsigned char rx_cnt;
> +	unsigned char rx_byte;
> +	unsigned char tx_cnt;
> +	unsigned char tx_byte;
> +	struct completion tx_done;
> +	struct mutex tx_mutex;
> +	struct delayed_work tx_work;
> +};
> +
> +static int ps2_gpio_open(struct serio *serio)
> +{
> +	struct ps2_gpio_data *drvdata = serio->port_data;
> +
> +	enable_irq(drvdata->irq);
> +	return 0;
> +}
> +
> +static void ps2_gpio_close(struct serio *serio)
> +{
> +	struct ps2_gpio_data *drvdata = serio->port_data;
> +
> +	disable_irq(drvdata->irq);
> +}
> +
> +static int __ps2_gpio_write(struct serio *serio, unsigned char val)
> +{
> +	struct ps2_gpio_data *drvdata = serio->port_data;
> +
> +	disable_irq_nosync(drvdata->irq);
> +	gpiod_direction_output(drvdata->gpio_clk, 0);
> +
> +	drvdata->mode = PS2_MODE_TX;
> +	drvdata->tx_byte = val;
> +
> +	schedule_delayed_work(&drvdata->tx_work, usecs_to_jiffies(200));
> +
> +	return 0;
> +}
> +
> +static int ps2_gpio_write(struct serio *serio, unsigned char val)
> +{
> +	struct ps2_gpio_data *drvdata = serio->port_data;
> +	int ret = 0;
> +
> +	if (in_task()) {
> +		mutex_lock(&drvdata->tx_mutex);
> +		__ps2_gpio_write(serio, val);
> +		if (!wait_for_completion_timeout(&drvdata->tx_done,
> +						 msecs_to_jiffies(10000)))
> +			ret = SERIO_TIMEOUT;
> +		mutex_unlock(&drvdata->tx_mutex);
> +	} else {
> +		__ps2_gpio_write(serio, val);
> +	}
> +
> +	return ret;
> +}
> +
> +static void ps2_gpio_tx_work_fn(struct work_struct *work)
> +{
> +	struct delayed_work *dwork = to_delayed_work(work);
> +	struct ps2_gpio_data *drvdata = container_of(dwork,
> +						    struct ps2_gpio_data,
> +						    tx_work);
> +
> +	enable_irq(drvdata->irq);
> +	gpiod_direction_output(drvdata->gpio_data, 0);
> +	gpiod_direction_input(drvdata->gpio_clk);
> +}
> +
> +static irqreturn_t ps2_gpio_irq_rx(struct ps2_gpio_data *drvdata)
> +{
> +	unsigned char byte, cnt;
> +	int data;
> +	int rxflags = 0;
> +	static unsigned long old_jiffies;
> +
> +	byte = drvdata->rx_byte;
> +	cnt = drvdata->rx_cnt;
> +
> +	if (old_jiffies == 0)
> +		old_jiffies = jiffies;
> +
> +	if ((jiffies - old_jiffies) > usecs_to_jiffies(100)) {
> +		dev_err(drvdata->dev,
> +			"RX: timeout, probably we missed an interrupt\n");
> +		goto err;
> +	}
> +	old_jiffies = jiffies;
> +
> +	data = gpiod_get_value(drvdata->gpio_data);
> +	if (unlikely(data < 0)) {
> +		dev_err(drvdata->dev, "RX: failed to get data gpio val: %d\n",
> +			data);
> +		goto err;
> +	}
> +
> +	switch (cnt) {
> +	case PS2_START_BIT:
> +		/* start bit should be low */
> +		if (unlikely(data)) {
> +			dev_err(drvdata->dev, "RX: start bit should be low\n");
> +			goto err;
> +		}
> +		break;
> +	case PS2_DATA_BIT0:
> +	case PS2_DATA_BIT1:
> +	case PS2_DATA_BIT2:
> +	case PS2_DATA_BIT3:
> +	case PS2_DATA_BIT4:
> +	case PS2_DATA_BIT5:
> +	case PS2_DATA_BIT6:
> +	case PS2_DATA_BIT7:
> +		/* processing data bits */
> +		if (data)
> +			byte |= (data << (cnt - 1));
> +		break;
> +	case PS2_PARITY_BIT:
> +		/* check odd parity */
> +		if (!((hweight8(byte) & 1) ^ data)) {
> +			rxflags |= SERIO_PARITY;
> +			dev_warn(drvdata->dev, "RX: parity error\n");
> +			if (!drvdata->write_enable)
> +				goto err;
> +		}
> +
> +		/* Do not send spurious ACK's and NACK's when write fn is
> +		 * not provided.
> +		 */
> +		if (!drvdata->write_enable) {
> +			if (byte == PS2_DEV_RET_NACK)
> +				goto err;
> +			else if (byte == PS2_DEV_RET_ACK)
> +				break;
> +		}
> +
> +		/* Let's send the data without waiting for the stop bit to be
> +		 * sent. It may happen that we miss the stop bit. When this
> +		 * happens we have no way to recover from this, certainly
> +		 * missing the parity bit would be recognized when processing
> +		 * the stop bit. When missing both, data is lost.
> +		 */
> +		serio_interrupt(drvdata->serio, byte, rxflags);
> +		dev_dbg(drvdata->dev, "RX: sending byte 0x%x\n", byte);
> +		break;
> +	case PS2_STOP_BIT:
> +		/* stop bit should be high */
> +		if (unlikely(!data)) {
> +			dev_err(drvdata->dev, "RX: stop bit should be high\n");
> +			goto err;
> +		}
> +		cnt = byte = 0;
> +		old_jiffies = 0;
> +		goto end; /* success */
> +	default:
> +		dev_err(drvdata->dev, "RX: got out of sync with the device\n");
> +		goto err;
> +	}
> +
> +	cnt++;
> +	goto end; /* success */
> +
> +err:
> +	cnt = byte = 0;
> +	old_jiffies = 0;
> +	__ps2_gpio_write(drvdata->serio, PS2_CMD_RESEND);
> +end:
> +	drvdata->rx_cnt = cnt;
> +	drvdata->rx_byte = byte;
> +	return IRQ_HANDLED;
> +}
> +
> +static irqreturn_t ps2_gpio_irq_tx(struct ps2_gpio_data *drvdata)
> +{
> +	unsigned char byte, cnt;
> +	int data;
> +	static unsigned long old_jiffies;
> +
> +	cnt = drvdata->tx_cnt;
> +	byte = drvdata->tx_byte;
> +
> +	if (old_jiffies == 0)
> +		old_jiffies = jiffies;
> +
> +	if ((jiffies - old_jiffies) > usecs_to_jiffies(100)) {
> +		dev_err(drvdata->dev,
> +			"TX: timeout, probably we missed an interrupt\n");
> +		goto err;
> +	}
> +	old_jiffies = jiffies;
> +
> +	switch (cnt) {
> +	case PS2_START_BIT:
> +		/* should never happen */
> +		dev_err(drvdata->dev,
> +			"TX: start bit should have been sent already\n");
> +		goto err;
> +	case PS2_DATA_BIT0:
> +	case PS2_DATA_BIT1:
> +	case PS2_DATA_BIT2:
> +	case PS2_DATA_BIT3:
> +	case PS2_DATA_BIT4:
> +	case PS2_DATA_BIT5:
> +	case PS2_DATA_BIT6:
> +	case PS2_DATA_BIT7:
> +		data = byte & BIT(cnt - 1);
> +		gpiod_set_value(drvdata->gpio_data, data);
> +		break;
> +	case PS2_PARITY_BIT:
> +		/* do odd parity */
> +		data = !(hweight8(byte) & 1);
> +		gpiod_set_value(drvdata->gpio_data, data);
> +		break;
> +	case PS2_STOP_BIT:
> +		/* release data line to generate stop bit */
> +		gpiod_direction_input(drvdata->gpio_data);
> +		break;
> +	case PS2_TX_TIMEOUT:
> +		/* Devices generate one extra clock pulse before sending the
> +		 * acknowledgment.
> +		 */
> +		break;
> +	case PS2_ACK_BIT:
> +		gpiod_direction_input(drvdata->gpio_data);
> +		data = gpiod_get_value(drvdata->gpio_data);
> +		if (data) {
> +			dev_warn(drvdata->dev, "TX: received NACK, retry\n");
> +			goto err;
> +		}
> +
> +		drvdata->mode = PS2_MODE_RX;
> +		complete(&drvdata->tx_done);
> +
> +		cnt = 1;
> +		old_jiffies = 0;
> +		goto end; /* success */
> +	default:
> +		/* Probably we missed the stop bit. Therefore we release data
> +		 * line and try again.
> +		 */
> +		gpiod_direction_input(drvdata->gpio_data);
> +		dev_err(drvdata->dev, "TX: got out of sync with the device\n");
> +		goto err;
> +	}
> +
> +	cnt++;
> +	goto end; /* success */
> +
> +err:
> +	cnt = 1;
> +	old_jiffies = 0;
> +	gpiod_direction_input(drvdata->gpio_data);
> +	__ps2_gpio_write(drvdata->serio, drvdata->tx_byte);
> +end:
> +	drvdata->tx_cnt = cnt;
> +	return IRQ_HANDLED;
> +}
> +
> +static irqreturn_t ps2_gpio_irq(int irq, void *dev_id)
> +{
> +	struct ps2_gpio_data *drvdata = dev_id;
> +
> +	return drvdata->mode ? ps2_gpio_irq_tx(drvdata) :
> +		ps2_gpio_irq_rx(drvdata);
> +}
> +
> +static int ps2_gpio_get_props(struct device *dev,
> +				 struct ps2_gpio_data *drvdata)
> +{
> +	drvdata->gpio_data = devm_gpiod_get(dev, "data", GPIOD_IN);
> +	if (IS_ERR(drvdata->gpio_data)) {
> +		dev_err(dev, "failed to request data gpio: %ld",
> +			PTR_ERR(drvdata->gpio_data));
> +		return PTR_ERR(drvdata->gpio_data);
> +	}
> +
> +	drvdata->gpio_clk = devm_gpiod_get(dev, "clk", GPIOD_IN);
> +	if (IS_ERR(drvdata->gpio_clk)) {
> +		dev_err(dev, "failed to request clock gpio: %ld",
> +			PTR_ERR(drvdata->gpio_clk));
> +		return PTR_ERR(drvdata->gpio_clk);
> +	}
> +
> +	drvdata->write_enable = device_property_read_bool(dev,
> +				"write-enable");
> +
> +	return 0;
> +}
> +
> +static int ps2_gpio_probe(struct platform_device *pdev)
> +{
> +	struct ps2_gpio_data *drvdata;
> +	struct serio *serio;
> +	struct device *dev = &pdev->dev;
> +	int error;
> +
> +	drvdata = devm_kzalloc(dev, sizeof(struct ps2_gpio_data), GFP_KERNEL);
> +	serio = kzalloc(sizeof(struct serio), GFP_KERNEL);
> +	if (!drvdata || !serio) {
> +		error = -ENOMEM;
> +		goto err_free_serio;
> +	}
> +
> +	error = ps2_gpio_get_props(dev, drvdata);
> +	if (error)
> +		goto err_free_serio;
> +
> +	if (gpiod_cansleep(drvdata->gpio_data) ||
> +	    gpiod_cansleep(drvdata->gpio_clk)) {
> +		dev_err(dev, "GPIO data or clk are connected via slow bus\n");
> +		error = -EINVAL;
> +	}
> +
> +	drvdata->irq = platform_get_irq(pdev, 0);
> +	if (drvdata->irq < 0) {
> +		dev_err(dev, "failed to get irq from platform resource: %d\n",
> +			drvdata->irq);
> +		error = drvdata->irq;
> +		goto err_free_serio;
> +	}
> +
> +	error = devm_request_irq(dev, drvdata->irq, ps2_gpio_irq,
> +				 IRQF_NO_THREAD, DRIVER_NAME, drvdata);
> +	if (error) {
> +		dev_err(dev, "failed to request irq %d: %d\n",
> +			drvdata->irq, error);
> +		goto err_free_serio;
> +	}
> +
> +	/* Keep irq disabled until serio->open is called. */
> +	disable_irq(drvdata->irq);
> +
> +	serio->id.type = SERIO_8042;
> +	serio->open = ps2_gpio_open;
> +	serio->close = ps2_gpio_close;
> +	/* Write can be enabled in platform/dt data, but possibly it will not
> +	 * work because of the tough timings.
> +	 */
> +	serio->write = drvdata->write_enable ? ps2_gpio_write : NULL;
> +	serio->port_data = drvdata;
> +	serio->dev.parent = dev;
> +	strlcpy(serio->name, dev_name(dev), sizeof(serio->name));
> +	strlcpy(serio->phys, dev_name(dev), sizeof(serio->phys));
> +
> +	drvdata->serio = serio;
> +	drvdata->dev = dev;
> +	drvdata->mode = PS2_MODE_RX;
> +
> +	/* Tx count always starts at 1, as the start bit is sent implicitly by
> +	 * host-to-device communication initialization.
> +	 */
> +	drvdata->tx_cnt = 1;
> +
> +	INIT_DELAYED_WORK(&drvdata->tx_work, ps2_gpio_tx_work_fn);
> +	init_completion(&drvdata->tx_done);
> +	mutex_init(&drvdata->tx_mutex);
> +
> +	serio_register_port(serio);
> +	platform_set_drvdata(pdev, drvdata);
> +
> +	return 0;	/* success */
> +
> +err_free_serio:
> +	kfree(serio);
> +	return error;
> +}
> +
> +static int ps2_gpio_remove(struct platform_device *pdev)
> +{
> +	struct ps2_gpio_data *drvdata = platform_get_drvdata(pdev);
> +
> +	serio_unregister_port(drvdata->serio);
> +	return 0;
> +}
> +
> +#if defined(CONFIG_OF)
> +static const struct of_device_id ps2_gpio_match[] = {
> +	{ .compatible = "ps2-gpio", },
> +	{ },
> +};
> +MODULE_DEVICE_TABLE(of, ps2_gpio_match);
> +#endif
> +
> +static struct platform_driver ps2_gpio_driver = {
> +	.probe		= ps2_gpio_probe,
> +	.remove		= ps2_gpio_remove,
> +	.driver = {
> +		.name = DRIVER_NAME,
> +		.of_match_table = of_match_ptr(ps2_gpio_match),
> +	},
> +};
> +module_platform_driver(ps2_gpio_driver);
> +
> +MODULE_AUTHOR("Danilo Krummrich <danilokrummrich@...develop.de>");
> +MODULE_DESCRIPTION("GPIO PS2 driver");
> +MODULE_LICENSE("GPL v2");
> -- 
> 2.14.1
> 

-- 
Dmitry

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