[PATCH v4 2/3] button: add a simple Analog to Digital Converter device based button driver

[Heinrich Schuchardt]

On 12/22/20 9:56 AM, Marek Szyprowski wrote:
> Add a simple Analog to Digital Converter device based button driver. This
> driver binds to the 'adc-keys' device tree node.
>
> Signed-off-by: Marek Szyprowski <m.szyprowski at samsung.com>
> ---
>   drivers/button/Kconfig      |   8 +++
>   drivers/button/Makefile     |   1 +
>   drivers/button/button-adc.c | 121 ++++++++++++++++++++++++++++++++++++
>   3 files changed, 130 insertions(+)
>   create mode 100644 drivers/button/button-adc.c
>
> diff --git a/drivers/button/Kconfig b/drivers/button/Kconfig
> index 6b3ec7e55d..6db3c5e93a 100644
> --- a/drivers/button/Kconfig
> +++ b/drivers/button/Kconfig
> @@ -9,6 +9,14 @@ config BUTTON
>   	  can provide access to board-specific buttons. Use of the device tree
>   	  for configuration is encouraged.
>
> +config BUTTON_ADC
> +	bool "Button adc"
> +	depends on BUTTON
> +	help
> +	  Enable support for buttons which are connected to Analog to Digital
> +	  Converter device. The ADC driver must use driver model. Buttons are
> +	  configured using the device tree.
> +
>   config BUTTON_GPIO
>   	bool "Button gpio"
>   	depends on BUTTON
> diff --git a/drivers/button/Makefile b/drivers/button/Makefile
> index fcc10ebe8d..bbd18af149 100644
> --- a/drivers/button/Makefile
> +++ b/drivers/button/Makefile
> @@ -3,4 +3,5 @@
>   # Copyright (C) 2020 Philippe Reynes <philippe.reynes at softathome.com>
>
>   obj-$(CONFIG_BUTTON) += button-uclass.o
> +obj-$(CONFIG_BUTTON_ADC) += button-adc.o
>   obj-$(CONFIG_BUTTON_GPIO) += button-gpio.o
> diff --git a/drivers/button/button-adc.c b/drivers/button/button-adc.c
> new file mode 100644
> index 0000000000..bf99dd8b43
> --- /dev/null
> +++ b/drivers/button/button-adc.c
> @@ -0,0 +1,121 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2020 Samsung Electronics Co., Ltd.
> + *		http://www.samsung.com
> + * Author: Marek Szyprowski <m.szyprowski at samsung.com>
> + */
> +
> +#include <common.h>
> +#include <adc.h>
> +#include <button.h>
> +#include <dm.h>
> +#include <dm/lists.h>
> +#include <dm/uclass-internal.h>
> +
> +/**
> + * struct button_adc_priv - private data for button-adc driver.
> + *
> + * @adc: Analog to Digital Converter device to which button is connected.
> + * @channel: channel of the ADC device to probe the button state.
> + */
> +struct button_adc_priv {
> +	struct udevice *adc;
> +	int channel;
> +};
> +
> +static enum button_state_t button_adc_get_state(struct udevice *dev)
> +{
> +	struct button_adc_priv *priv = dev_get_priv(dev);
> +	unsigned int val, mask;
> +	int ret;
> +
> +	ret = adc_start_channel(priv->adc, priv->channel);
> +	if (ret)
> +		return ret;
> +
> +	ret = adc_channel_data(priv->adc, priv->channel, &val);
> +	if (ret)
> +		return ret;
> +
> +	ret = adc_data_mask(priv->adc, &mask);
> +	if (ret)
> +		return ret;
> +
> +	/* getting state is simplified a bit */
> +	if (ret == 0)
> +		return (val < mask / 2) ? BUTTON_ON : BUTTON_OFF;
> +
> +	return ret;
> +}
> +
> +static int button_adc_probe(struct udevice *dev)
> +{
> +	struct button_uc_plat *uc_plat = dev_get_uclass_platdata(dev);
> +	struct button_adc_priv *priv = dev_get_priv(dev);
> +	struct ofnode_phandle_args args;
> +	int ret;
> +
> +	/* Ignore the top-level button node */
> +	if (!uc_plat->label)
> +		return 0;
> +
> +	ret = dev_read_phandle_with_args(dev->parent, "io-channels",
> +					 "#io-channel-cells", 0, 0, &args);
> +	if (ret)
> +		return ret;
> +
> +	ret = uclass_get_device_by_ofnode(UCLASS_ADC, args.node, &priv->adc);
> +	if (ret)
> +		return ret;
> +
> +	priv->channel = args.args[0];
> +
> +	return ret;
> +}
> +
> +static int button_adc_bind(struct udevice *parent)
> +{
> +	struct udevice *dev;
> +	ofnode node;
> +	int ret;
> +
> +	dev_for_each_subnode(node, parent) {
> +		struct button_uc_plat *uc_plat;
> +		const char *label;
> +
> +		label = ofnode_read_string(node, "label");
> +		if (!label) {
> +			debug("%s: node %s has no label\n", __func__,
> +			      ofnode_get_name(node));
> +			return -EINVAL;
> +		}
> +		ret = device_bind_driver_to_node(parent, "button_adc",
> +						 ofnode_get_name(node),
> +						 node, &dev);

This code does not match the binding. The binding defines a voltage
ladder where you have multiple voltage ranges and multiple buttons.

You need to consider the threshold voltages.

Have a look at Linux' drivers/input/keyboard/adc-keys.c. Beware that
code is also incorrect as the author ignores the meaning of "threshold"
and uses it it as closest voltage.

Best regards

Heinrich

> +		if (ret)
> +			return ret;
> +		uc_plat = dev_get_uclass_platdata(dev);
> +		uc_plat->label = label;
> +	}
> +
> +	return 0;
> +}
> +
> +static const struct button_ops button_adc_ops = {
> +	.get_state	= button_adc_get_state,
> +};
> +
> +static const struct udevice_id button_adc_ids[] = {
> +	{ .compatible = "adc-keys" },
> +	{ }
> +};
> +
> +U_BOOT_DRIVER(button_adc) = {
> +	.name		= "button_adc",
> +	.id		= UCLASS_BUTTON,
> +	.of_match	= button_adc_ids,
> +	.ops		= &button_adc_ops,
> +	.priv_auto_alloc_size = sizeof(struct button_adc_priv),
> +	.bind		= button_adc_bind,
> +	.probe		= button_adc_probe,
> +};
>