Re: [PATCH v3] serio: PS/2 gpio bit banging driver for the serio bus

[Dmitry Torokhov]

Hi Danilo,

On Tue, Aug 01, 2017 at 06:26:14AM +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 static platform data.
> 
> Writing to a device is supported as well, though it is not recommended as
> the timings to be halt given by libps2 are very tough and difficult to
> reach with bit banging. Therefore it can be configured (also in DT and
> pdata) whether the serio write function should be available for clients.
> 
> This driver is for development purposes and not 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 a RPI1 and on Hikey960 and it worked well
> together with the atkbd driver.
> 
> Signed-off-by: Danilo Krummrich <danilokrummrich@xxxxxxxxxxxxx>
> ---
> v2: Removed one verbose print statement, changed another one to dev_dbg.
> v3: - fixed compiler warning on blackfin
>     - depends on GPIOLIB
>     - clarify documentation
> ---
>  .../devicetree/bindings/serio/ps2-gpio.txt         |  20 +
>  Documentation/gpio/drivers-on-gpio.txt             |   5 +
>  drivers/input/serio/Kconfig                        |  11 +
>  drivers/input/serio/Makefile                       |   1 +
>  drivers/input/serio/ps2-gpio.c                     | 439 +++++++++++++++++++++
>  include/linux/ps2-gpio.h                           |  27 ++
>  6 files changed, 503 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/serio/ps2-gpio.txt
>  create mode 100644 drivers/input/serio/ps2-gpio.c
>  create mode 100644 include/linux/ps2-gpio.h
> 
> diff --git a/Documentation/devicetree/bindings/serio/ps2-gpio.txt b/Documentation/devicetree/bindings/serio/ps2-gpio.txt
> new file mode 100644
> index 0000000..828a5b6
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/serio/ps2-gpio.txt
> @@ -0,0 +1,20 @@
> +Device-Tree bindings for ps2 gpio driver
> +
> +Required properties:
> +	- compatible = "ps2-gpio";
> +	- gpios: data and clock gpio
> +
> +Optional properties:
> +	- ps2-gpio,write-enable: Indicates whether write function is provided
> +	to serio device. Most probably providing the write fn will not work,
> +	because of the tough timing libps2 requires.
> +
> +Example nodes:
> +
> +ps2@0 {
> +	compatible = "ps2-gpio";
> +	gpios = <&gpio 24 0 /* data */
> +		 &gpio 23 0 /* clock */
> +		>;
> +	i2c-gpio,write-enable = <0>;
> +};
> diff --git a/Documentation/gpio/drivers-on-gpio.txt b/Documentation/gpio/drivers-on-gpio.txt
> index 3065132..97c8716 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 an 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 c3d05b4..292d6e2 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 gpio-ps2.
> +
> +	  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 2374ef9..767bd9b 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 0000000..fc5368b
> --- /dev/null
> +++ b/drivers/input/serio/ps2-gpio.c
> @@ -0,0 +1,439 @@
> +/*
> + * GPIO based serio bus driver for bit banging the PS/2 protocol
> + *
> + * Author: Danilo Krummrich <danilokrummrich@xxxxxxxxxxxxx>
> + *
> + * 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.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/ps2-gpio.h>
> +#include <linux/of.h>
> +#include <linux/of_gpio.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_ACK_BIT		11
> +
> +#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;
> +	unsigned int gpio_clk;
> +	unsigned int gpio_data;
> +	unsigned int write_enable;
> +	unsigned int irq;
> +	unsigned char rx_cnt;
> +	unsigned char rx_byte;
> +	unsigned char tx_cnt;
> +	unsigned char tx_byte;
> +	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;
> +
> +	drvdata->mode = PS2_MODE_TX;
> +	drvdata->tx_byte = val;
> +	/* Make sure ISR running on other CPU notice changes. */
> +	barrier();
> +	disable_irq_nosync(drvdata->irq);

Why do you need to disable IRQ here? Shouldn't you let the device
complete transmitting the current byte (if any)?

> +	gpio_direction_output(drvdata->gpio_clk, 0);
> +	schedule_delayed_work(&drvdata->tx_work, usecs_to_jiffies(200));

What do we do if there are concurrent requests? The function returns
before it completes write.

> +
> +	return 0;
> +}
> +
> +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 = gpio_get_value(drvdata->gpio_data);
> +	if (unlikely(data < 0)) {
> +		dev_err(drvdata->dev, "RX: failed to get gpio %u value: %d\n",
> +			drvdata->gpio_data, 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;
> +		}
> +		/* 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.
> +		 * Additionally, we do not send spurious ACK's and NACK's.
> +		 */
> +		if (byte == PS2_DEV_RET_NACK)
> +			goto err;
> +		if (byte == PS2_DEV_RET_ACK)
> +			break;
> +		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 & (1 << (cnt - 1));

		data = byte & BIT(cnt - 1);

> +		gpio_set_value(drvdata->gpio_data, data);
> +		break;
> +	case PS2_PARITY_BIT:
> +		/* do odd parity */
> +		data = !(hweight8(byte) & 1);
> +		gpio_set_value(drvdata->gpio_data, data);
> +		break;
> +	case PS2_STOP_BIT:
> +		/* release data line to generate stop bit */
> +		gpio_direction_input(drvdata->gpio_data);
> +		break;
> +	case PS2_ACK_BIT:
> +		gpio_direction_input(drvdata->gpio_data);
> +		data = gpio_get_value(drvdata->gpio_data);
> +		if (data)
> +			dev_warn(drvdata->dev, "TX: received NACK, retry\n");
> +		if (data)
> +			goto err;
> +		drvdata->mode = PS2_MODE_RX;
> +		/* Make sure ISR running on other CPU notice mode change. */
> +		barrier();
> +		cnt = 1;
> +		old_jiffies = 0;
> +		goto end; /* success */
> +	default:
> +		/* Probably we missed the stop bit. Therefore we release data
> +		 * line and try again.
> +		 */
> +		gpio_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;
> +	gpio_direction_input(drvdata->gpio_data);
> +	ps2_gpio_write(drvdata->serio, PS2_CMD_RESEND);
> +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 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);
> +	gpio_direction_output(drvdata->gpio_data, 0);
> +	gpio_direction_input(drvdata->gpio_clk);
> +}
> +
> +static int of_ps2_gpio_get_props(struct device *dev,
> +				 struct ps2_gpio_data *drvdata)
> +{
> +	if (of_gpio_count(dev->of_node) < 2)
> +		return -ENODEV;
> +
> +	drvdata->gpio_data = of_get_gpio(dev->of_node, 0);
> +	drvdata->gpio_clk = of_get_gpio(dev->of_node, 1);

No, please use gpiod API and simply do:

	drvdata->gpio_data = devm_gpiod_get(dev, "data", GPIOD_IN);
	if (IS_ERR(drvdata->gpio_data)
		...

	drvdata->gpio_clk = devm_gpiod_get(dev, "clk", GPIOD_IN);
	if (IS_ERR(drvdata->gpio_clk)
		...

> +
> +	if (drvdata->gpio_data == -EPROBE_DEFER ||
> +	    drvdata->gpio_clk == -EPROBE_DEFER)
> +		return -EPROBE_DEFER;
> +
> +	if (!gpio_is_valid(drvdata->gpio_data) ||
> +	    !gpio_is_valid(drvdata->gpio_clk)) {
> +		dev_err(dev, "invalid GPIOs, data=%d, clk=%d\n",
> +			drvdata->gpio_data, drvdata->gpio_clk);
> +		return -ENODEV;
> +	}
> +
> +	of_property_read_u32(dev->of_node, "ps2-gpio,write-enable",
> +			     &drvdata->write_enable);

	device_property_read_bool(dev, ...);

> +
> +	return 0;
> +}
> +
> +static int ps2_gpio_probe(struct platform_device *pdev)
> +{
> +	struct ps2_gpio_data *drvdata;
> +	struct ps2_gpio_platform_data *pdata;
> +	struct serio *serio;
> +	struct device *dev = &pdev->dev;
> +	unsigned int irq;
> +	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;
> +	}
> +
> +	if (dev->of_node) {
> +		error = of_ps2_gpio_get_props(dev, drvdata);
> +		if (error)
> +			goto err_free_serio;
> +	} else {
> +		if (!dev_get_platdata(dev)) {
> +			error = -ENXIO;
> +			goto err_free_serio;
> +		}
> +		pdata = dev_get_platdata(dev);

I'd rather we did not add any more platform data but relied on generic
device properties (which are available on static boards, in addition to
OF and ACPI systems).

> +		drvdata->gpio_data = pdata->gpio_data;
> +		drvdata->gpio_clk = pdata->gpio_clk;
> +		drvdata->write_enable = pdata->write_enable;
> +	}
> +
> +	error = devm_gpio_request(dev, drvdata->gpio_clk, "ps2 clk");
> +	if (error) {
> +		dev_err(dev, "failed to request gpio %u: %d",
> +				drvdata->gpio_clk, error);
> +		goto err_free_serio;
> +	}
> +
> +	error = devm_gpio_request(dev, drvdata->gpio_data, "ps2 data");
> +	if (error) {
> +		dev_err(dev, "failed to request gpio %u: %d",
> +				drvdata->gpio_data, error);
> +		goto err_free_serio;
> +	}
> +
> +	gpio_direction_input(drvdata->gpio_clk);
> +	gpio_direction_input(drvdata->gpio_data);
> +
> +	irq = gpio_to_irq(drvdata->gpio_clk);
> +	if (!irq) {
> +		dev_err(dev, "cannot get irq from gpio %u\n",
> +			drvdata->gpio_clk);
> +		error = -ENXIO;
> +		goto err_free_serio;
> +	}


IRQ line does not have to be the same as GPIO pin. Describe it
separately in device properties and just do:

	irq = platform_get_irq(pdev, 0);

and use it in the request below.

> +
> +	error = devm_request_irq(dev, irq, ps2_gpio_irq, IRQF_NO_THREAD |
> +			IRQF_TRIGGER_FALLING, DRIVER_NAME, drvdata);

This will not work if GPIO is behind I2C or other slow bus. Is it
essential that there is no scheduling delay here?

> +	if (error) {
> +		dev_err(dev, "failed to request irq %u: %d\n",
> +			drvdata->irq, error);
> +		goto err_free_serio;
> +	}
> +
> +	serio->id.type = SERIO_8042;
> +	serio->open = ps2_gpio_open;
> +	serio->close = ps2_gpio_close;
> +	/* Write can be enabled in platform/dt data, but most probably 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->irq = irq;
> +	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);
> +
> +	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 = ps2_gpio_match,
> +	},
> +};
> +module_platform_driver(ps2_gpio_driver);
> +
> +MODULE_AUTHOR("Danilo Krummrich <danilokrummrich@xxxxxxxxxxxxx>");
> +MODULE_DESCRIPTION("GPIO PS2 driver");
> +MODULE_LICENSE("GPL v2");
> diff --git a/include/linux/ps2-gpio.h b/include/linux/ps2-gpio.h
> new file mode 100644
> index 0000000..b65480d
> --- /dev/null
> +++ b/include/linux/ps2-gpio.h
> @@ -0,0 +1,27 @@
> +/*
> + * ps2-gpio interface to platform code
> + *
> + * Author: Danilo Krummrich <danilokrummrich@xxxxxxxxxxxxx>
> + *
> + * 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.
> + */
> +#ifndef _LINUX_PS2_GPIO_H
> +#define _LINUX_PS2_GPIO_H
> +
> +/**
> + * struct ps2_gpio_platform_data - Platform-dependent data for ps2-gpio
> + * @gpio_data: GPIO pin ID to use for DATA
> + * @gpio_clk: GPIO pin ID to use for CLOCK
> + * @write_enable: Indicates whether write function is provided to serio
> + *	device. Most probably providing the write fn will not work,
> + *	because of the tough timing libps2 requires.
> + */
> +struct ps2_gpio_platform_data {
> +	unsigned int	gpio_data;
> +	unsigned int	gpio_clk;
> +	unsigned int	write_enable;
> +};
> +
> +#endif /* _LINUX_PS2_GPIO_H */
> -- 
> 2.9.3
> 

Thanks.

-- 
Dmitry