Re: [PATCH v2 1/2] input: misc: Add generic input driver to read encoded GPIO lines

[Dmitry Torokhov]

On Tue, Aug 23, 2016 at 10:27:59AM -0500, Andrew F. Davis wrote:
> On 08/23/2016 01:16 AM, Vignesh R wrote:
> > Add a driver to read group of GPIO lines and provide its status as a
> > numerical value as input event to the system. This will help in
> > intefacing devices, that can be connected over GPIOs, that provide input
> > to the system by driving GPIO lines connected to them like a rotary dial
> > or a switch.
> > 
> > For example, a rotary switch can be connected to four GPIO lines. The
> > status of the GPIO lines reflect the actual position of the rotary
> > switch dial. For example, if dial points to 9, then the four GPIO lines
> > connected to the switch will read HLLH(0b'1001 = 9). This value
> > can be reported as an ABS_* event to the input subsystem.
> > 
> > Signed-off-by: Vignesh R <vigneshr@xxxxxx>
> > Acked-by: Rob Herring <robh@xxxxxxxxxx>
> > ---
> > 
> > v2: Use decoder,max-value instead of gpio-decoder,max-value.
> > 
> >  .../devicetree/bindings/input/gpio-decoder.txt     |  23 ++++
> >  drivers/input/misc/Kconfig                         |  12 ++
> >  drivers/input/misc/Makefile                        |   1 +
> >  drivers/input/misc/gpio_decoder.c                  | 130 +++++++++++++++++++++
> >  4 files changed, 166 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/input/gpio-decoder.txt
> >  create mode 100644 drivers/input/misc/gpio_decoder.c
> > 
> > diff --git a/Documentation/devicetree/bindings/input/gpio-decoder.txt b/Documentation/devicetree/bindings/input/gpio-decoder.txt
> > new file mode 100644
> > index 000000000000..f27f083a9075
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/input/gpio-decoder.txt
> > @@ -0,0 +1,23 @@
> > +* GPIO Decoder DT bindings
> > +
> > +Required Properties:
> > +- compatible: should be "gpio-decoder"
> > +- gpios: a spec of gpios (atleast two) to be decoded to a number with
> 
>                               ^^ two words
> 
> > +  first entry representing the MSB.
> > +
> > +Optional Properties:
> > +- decoder,max-value: Maximum possible value that can be reported by
> > +  the gpios.
> > +- linux,axis: the input subsystem axis to map to (ABS_X/ABS_Y).
> > +  Defaults to 0 (ABS_X).
> > +
> > +Example:
> > +	gpio-decoder0 {
> > +		compatible = "gpio-decoder";
> > +		gpios = <&pca9536 3 GPIO_ACTIVE_HIGH>,
> > +			<&pca9536 2 GPIO_ACTIVE_HIGH>,
> > +			<&pca9536 1 GPIO_ACTIVE_HIGH>,
> > +			<&pca9536 0 GPIO_ACTIVE_HIGH>;
> > +		linux,axis = <0>; /* ABS_X */
> > +		decoder,max-value = <9>;
> > +	};
> > diff --git a/drivers/input/misc/Kconfig b/drivers/input/misc/Kconfig
> > index efb0ca871327..c44513cac3b7 100644
> > --- a/drivers/input/misc/Kconfig
> > +++ b/drivers/input/misc/Kconfig
> > @@ -292,6 +292,18 @@ config INPUT_GPIO_TILT_POLLED
> >  	  To compile this driver as a module, choose M here: the
> >  	  module will be called gpio_tilt_polled.
> >  
> > +config INPUT_GPIO_DECODER
> > +	tristate "Polled GPIO Decoder Input driver"
> > +	depends on GPIOLIB && OF
> > +	select INPUT_POLLDEV
> > +	help
> > +	 Say Y here if you want driver to read status of multiple GPIO
> > +	 lines and report the encoded value as an absolute integer to
> > +	 input subsystem.
> > +
> > +	 To compile this driver as a module, choose M here: the module
> > +	 will will be called gpio_decoder.
> > +
> >  config INPUT_IXP4XX_BEEPER
> >  	tristate "IXP4XX Beeper support"
> >  	depends on ARCH_IXP4XX
> > diff --git a/drivers/input/misc/Makefile b/drivers/input/misc/Makefile
> > index 6a1e5e20fc1c..0b6d025f0487 100644
> > --- a/drivers/input/misc/Makefile
> > +++ b/drivers/input/misc/Makefile
> > @@ -35,6 +35,7 @@ obj-$(CONFIG_INPUT_DRV2667_HAPTICS)	+= drv2667.o
> >  obj-$(CONFIG_INPUT_GP2A)		+= gp2ap002a00f.o
> >  obj-$(CONFIG_INPUT_GPIO_BEEPER)		+= gpio-beeper.o
> >  obj-$(CONFIG_INPUT_GPIO_TILT_POLLED)	+= gpio_tilt_polled.o
> > +obj-$(CONFIG_INPUT_GPIO_DECODER)	+= gpio_decoder.o
> >  obj-$(CONFIG_INPUT_HISI_POWERKEY)	+= hisi_powerkey.o
> >  obj-$(CONFIG_HP_SDC_RTC)		+= hp_sdc_rtc.o
> >  obj-$(CONFIG_INPUT_IMS_PCU)		+= ims-pcu.o
> > diff --git a/drivers/input/misc/gpio_decoder.c b/drivers/input/misc/gpio_decoder.c
> > new file mode 100644
> > index 000000000000..eec0fda6f562
> > --- /dev/null
> > +++ b/drivers/input/misc/gpio_decoder.c
> > @@ -0,0 +1,130 @@
> > +/*
> > + * gpio-decoder.c
> > + *
> 
> ^ the name of the file often changes without this being updated, it
> really doesn't add anything anyway, would recommend dropping it.
> 
> > + * A generic driver to reads multiple gpio lines and translate the
> > + * encoded numeric value into an input event.
> > + *
> > + * Copyright (C) 2016 Texas Instruments Incorporated - http://www.ti.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 version 2.
> > + *
> > + * This program is distributed "as is" WITHOUT ANY WARRANTY of any
> > + * kind, whether express or implied; without even the implied warranty
> > + * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + * GNU General Public License for more details.
> > + */
> > +
> > +#include <linux/device.h>
> > +#include <linux/gpio/consumer.h>
> > +#include <linux/input.h>
> > +#include <linux/input-polldev.h>
> > +#include <linux/kernel.h>
> > +#include <linux/module.h>
> > +#include <linux/of.h>
> > +#include <linux/platform_device.h>
> > +
> > +struct gpio_decoder {
> > +	struct input_polled_dev *poll_dev;
> > +	struct gpio_descs *input_gpios;
> > +	struct device *dev;
> > +	u32 axis;
> > +	u32 last_stable;
> > +};
> > +
> > +static unsigned int gpio_decoder_get_gpios_state(struct gpio_decoder
> > +						 *decoder)
> > +{
> > +	struct gpio_descs *gpios = decoder->input_gpios;
> > +	unsigned int ret = 0;
> > +	int i, val;
> > +
> > +	for (i = 0; i < gpios->ndescs; i++) {
> > +		val = gpiod_get_value_cansleep(gpios->desc[i]);
> > +		ret = ret << 1 | val;
> 
> Just to be safe, could you mask val with 0x1 here.

We also want to check for negative. So I guess:

		val = gpiod_get_value_cansleep(gpios->desc[i]);
		if (val >= 0)
			ret = (ret << 1) | !!val;

?

> 
> > +	}
> > +
> > +	return ret;
> > +}
> > +
> > +static void gpio_decoder_poll_gpios(struct input_polled_dev *poll_dev)
> > +{
> > +	struct gpio_decoder *decoder = poll_dev->private;
> > +	unsigned int state = gpio_decoder_get_gpios_state(decoder);
> > +
> > +	if (state != decoder->last_stable) {
> > +		input_report_abs(poll_dev->input, decoder->axis, state);
> > +		input_sync(poll_dev->input);
> > +		decoder->last_stable = state;
> > +	}
> > +}
> > +
> > +static int gpio_decoder_probe(struct platform_device *pdev)
> > +{
> > +	struct device *dev = &pdev->dev;
> > +	struct gpio_decoder *decoder;
> > +	struct input_polled_dev *poll_dev;
> > +	u32  max;
> > +	int err;
> > +
> > +	decoder = devm_kzalloc(dev, sizeof(struct gpio_decoder), GFP_KERNEL);
> > +	if (!decoder)
> > +		return -ENOMEM;
> > +
> > +	device_property_read_u32(dev, "linux,axis", &decoder->axis);
> > +	decoder->input_gpios = devm_gpiod_get_array(dev, NULL, GPIOD_IN);
> > +	if (IS_ERR(decoder->input_gpios)) {
> > +		dev_err(dev, "unable to acquire input gpios\n");
> > +		return PTR_ERR(decoder->input_gpios);
> > +	}
> > +	if (decoder->input_gpios->ndescs < 2) {
> > +		dev_err(dev, "not enough gpios found\n");
> > +		return -EINVAL;
> > +	}
> > +
> > +	if (device_property_read_u32(dev, "decoder,max-value", &max))
> > +		max = BIT(decoder->input_gpios->ndescs);
> > +
> > +	decoder->dev = dev;
> > +	poll_dev = devm_input_allocate_polled_device(decoder->dev);
> > +	if (!poll_dev)
> > +		return -ENOMEM;
> > +
> > +	poll_dev->private = decoder;
> > +	poll_dev->poll = gpio_decoder_poll_gpios;
> > +	decoder->poll_dev = poll_dev;
> > +
> > +	poll_dev->input->name = pdev->name;
> > +	poll_dev->input->id.bustype = BUS_HOST;
> > +	poll_dev->input->dev.parent = dev;

No need to set for devices allocated with
devm_input_allocate_polled_device.

> > +	input_set_abs_params(poll_dev->input, decoder->axis, 0, max, 0, 1);
> > +
> > +	err = input_register_polled_device(poll_dev);
> > +	if (err) {
> > +		dev_err(dev, "failed to register polled  device\n");
> > +		return err;
> > +	}
> > +	platform_set_drvdata(pdev, decoder);
> > +
> > +	return 0;
> > +}
> > +
> > +static const struct of_device_id gpio_decoder_of_match[] = {
> > +	{ .compatible = "gpio-decoder", },
> > +	{ },
> > +};
> > +MODULE_DEVICE_TABLE(of, gpio_decoder_of_match);
> > +
> > +static struct platform_driver gpio_decoder_driver = {
> > +	.probe		= gpio_decoder_probe,
> > +	.driver		= {
> > +		.name	= "gpio-decoder",
> > +		.of_match_table = of_match_ptr(gpio_decoder_of_match),
> 
> When the struct 'gpio_decoder_of_match' is always defined (not
> conditional on OF support), then 'of_match_ptr' does nothing and can be
> dropped here.

There is nothing in this driver that makes it OF-specific. I'd leave
of_match_ptr() as is, added #ifdef CONFIG_OF guard around
gpio_decoder_of_match, and changed "depends on GPIOLIB && OF" to
"depends on GPIOLIB || COMPILE_TEST".

Thanks.

> 
> > +	}
> > +};
> > +module_platform_driver(gpio_decoder_driver);
> > +
> > +MODULE_DESCRIPTION("GPIO decoder input driver");
> > +MODULE_AUTHOR("Vignesh R <vigneshr@xxxxxx>");
> > +MODULE_LICENSE("GPL v2");

-- 
Dmitry