Re: [PATCH 13/14] input: touchscreen: sama5d2_rts: SAMA5D2 Resistive touchscreen driver

[Jonathan Cameron]

On Fri, 22 Dec 2017 17:07:20 +0200
Eugen Hristev <eugen.hristev@xxxxxxxxxxxxx> wrote:

> This is the implementation of the Microchip SAMA5D2 SOC resistive
> touchscreen driver.
> The driver registers an input device and connects to the give IIO device
> from devicetree. It requires an IIO trigger (acting as a consumer) and
> three IIO channels : one for X position, one for Y position and one
> for pressure.
> It the reports the values to the input subsystem.
> 
> Some parts of this driver are based on the initial original work by
> Mohamed Jamsheeth Hajanajubudeen and Bandaru Venkateswara Swamy
> 
> Signed-off-by: Eugen Hristev <eugen.hristev@xxxxxxxxxxxxx>

I've suggested some difference in implementation, but this is very nearly
a generic resistive touch screen driver which is rather nice.

It does use somewhat magic trigger which is effectively a filtered
periodic trigger (only fires when touch has occurred) which would not
be particularly hard to implement in other resistive touch screen ADCs.
I'm not totally sure that is a strong requirement though - any periodic
trigger would work.

Anyhow, the big stuff to my mind is whether we can use the buffer_cb
code to do this.  I originally wrote that for an accelerometer to input
bridge driver (which I never got around to finishing upstreaming). It's
existing usecases are rather esoteric but it should work here I think.

Jonathan

> ---
>  drivers/input/touchscreen/Kconfig       |  13 ++
>  drivers/input/touchscreen/Makefile      |   1 +
>  drivers/input/touchscreen/sama5d2_rts.c | 287 ++++++++++++++++++++++++++++++++
>  3 files changed, 301 insertions(+)
>  create mode 100644 drivers/input/touchscreen/sama5d2_rts.c
> 
> diff --git a/drivers/input/touchscreen/Kconfig b/drivers/input/touchscreen/Kconfig
> index 64b30fe..db8f541 100644
> --- a/drivers/input/touchscreen/Kconfig
> +++ b/drivers/input/touchscreen/Kconfig
> @@ -126,6 +126,19 @@ config TOUCHSCREEN_ATMEL_MXT_T37
>  	  Say Y here if you want support to output data from the T37
>  	  Diagnostic Data object using a V4L device.
>  
> +config TOUCHSCREEN_SAMA5D2
> +	tristate "Microchip SAMA5D2 resistive touchscreen support"
> +	depends on ARCH_AT91
> +	depends on AT91_SAMA5D2_ADC
> +	help
> +	  Say Y here if you have 4-wire touchscreen connected
> +          to ADC Controller on your SAMA5D2 Microchip SoC.
> +
> +          If unsure, say N.
> +
> +          To compile this driver as a module, choose M here: the
> +          module will be called sama5d2_rts.
> +
>  config TOUCHSCREEN_AUO_PIXCIR
>  	tristate "AUO in-cell touchscreen using Pixcir ICs"
>  	depends on I2C
> diff --git a/drivers/input/touchscreen/Makefile b/drivers/input/touchscreen/Makefile
> index 850c156..9a2772e 100644
> --- a/drivers/input/touchscreen/Makefile
> +++ b/drivers/input/touchscreen/Makefile
> @@ -16,6 +16,7 @@ obj-$(CONFIG_TOUCHSCREEN_AD7879_SPI)	+= ad7879-spi.o
>  obj-$(CONFIG_TOUCHSCREEN_ADS7846)	+= ads7846.o
>  obj-$(CONFIG_TOUCHSCREEN_AR1021_I2C)	+= ar1021_i2c.o
>  obj-$(CONFIG_TOUCHSCREEN_ATMEL_MXT)	+= atmel_mxt_ts.o
> +obj-$(CONFIG_TOUCHSCREEN_SAMA5D2)	+= sama5d2_rts.o
>  obj-$(CONFIG_TOUCHSCREEN_AUO_PIXCIR)	+= auo-pixcir-ts.o
>  obj-$(CONFIG_TOUCHSCREEN_BU21013)	+= bu21013_ts.o
>  obj-$(CONFIG_TOUCHSCREEN_CHIPONE_ICN8318)	+= chipone_icn8318.o
> diff --git a/drivers/input/touchscreen/sama5d2_rts.c b/drivers/input/touchscreen/sama5d2_rts.c
> new file mode 100644
> index 0000000..e2ae413
> --- /dev/null
> +++ b/drivers/input/touchscreen/sama5d2_rts.c
> @@ -0,0 +1,287 @@
> +/*
> + * Microchip resistive touchscreen (RTS) driver for SAMA5D2.
> + *
> + * Copyright (C) 2017 Microchip Technology,
> + * Author: Eugen Hristev <eugen.hristev@xxxxxxxxxxxxx>
> + *
> + * SPDX-License-Identifier: GPL-2.0
> + */
> +#include <linux/input.h>
> +#include <linux/of.h>
> +#include <linux/of_device.h>
> +#include <linux/platform_device.h>
> +#include <linux/iio/consumer.h>
> +#include <linux/iio/trigger.h>
> +#include <linux/iio/trigger_consumer.h>
> +
> +#define DRIVER_NAME					"sama5d2_rts"
> +#define MAX_POS_MASK					GENMASK(11, 0)
> +#define AT91_RTS_DEFAULT_PRESSURE_THRESHOLD		10000
> +
> +/**
> + * at91_rts - at91 resistive touchscreen information struct
> + * @input:		the input device structure that we register
> + * @chan_x:		X channel to IIO device to get position on X axis
> + * @chan_y:		Y channel to IIO device to get position on Y axis
> + * @chan_pressure:	pressure channel to IIO device to get pressure
> + * @trig:		trigger to IIO device to register to for polling
> + * @rts_pf:		pollfunc for the trigger to be called by IIO dev
> + * @pressure_threshold:	number representing the threshold for the pressure
> + * @adc_connected:	to know if adc device is connected
> + * @workq:		to defer computations to this work queue for reporting
> + */
> +struct at91_rts {
> +	struct input_dev	*input;
> +	struct iio_channel	*chan_x, *chan_y, *chan_pressure;
> +	struct iio_trigger	*trig;
> +	struct iio_poll_func	*rts_pf;
> +	u32                     pressure_threshold;
> +	bool			adc_connected;
> +	struct work_struct	workq;
> +};
> +
> +static irqreturn_t at91_rts_trigger_handler(int irq, void *p)
> +{
> +	struct at91_rts *st = ((struct iio_poll_func *)p)->p;
> +
> +	schedule_work(&st->workq);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static void at91_rts_workq_handler(struct work_struct *workq)
> +{
> +	struct at91_rts *st = container_of(workq, struct at91_rts, workq);
> +	unsigned int x, y, press;
> +	int ret;
> +

If we were instead to use a callback buffer this would all be
in the ADC driver as a simple 3 element channel scan.

> +	/* read the channels, if all good, report touch */
> +	ret = iio_read_channel_raw(st->chan_x, &x);
> +	if (ret < 0)
> +		goto at91_rts_workq_handler_end_touch;
> +
> +	ret = iio_read_channel_raw(st->chan_y, &y);
> +	if (ret < 0)
> +		goto at91_rts_workq_handler_end_touch;
> +
> +	ret = iio_read_channel_raw(st->chan_pressure, &press);
> +	if (ret < 0)
> +		goto at91_rts_workq_handler_end_touch;
> +
At this point our callback would be called and provided the above data.

> +	/* if pressure too low, don't report */
> +	if (press > st->pressure_threshold)
> +		goto at91_rts_workq_handler_exit;
> +
> +	input_report_abs(st->input, ABS_X, x);
> +	input_report_abs(st->input, ABS_Y, y);
> +	input_report_abs(st->input, ABS_PRESSURE, press);
> +	input_report_key(st->input, BTN_TOUCH, 1);
> +	input_sync(st->input);
> +

This would be back in the callback buffer code once the
callback has run.

Has the interesting side effect of making this code effectively generic.
It no longer has any ties to the at91 at all that I can spot.
Just a selection of channels and a request for a particular trigger -
both of which could come from device tree.

> +	iio_trigger_notify_done(st->trig);
> +	return;
> +
> +at91_rts_workq_handler_end_touch:
> +	/* report end of touch */
> +	input_report_key(st->input, BTN_TOUCH, 0);
> +	input_sync(st->input);
> +at91_rts_workq_handler_exit:
> +	iio_trigger_notify_done(st->trig);
> +}
> +
> +static int at91_rts_open(struct input_dev *dev)
> +{
> +	int ret;
> +	struct at91_rts *st = input_get_drvdata(dev);
> +
> +	/* avoid multiple initialization in case touchscreen is opened again */
> +	if (st->adc_connected)
> +		return 0;
> +
> +	/*
> +	 * First, look for the channels. It is possible that the ADC device
> +	 * did not probe yet, but we already probed, so we returning probe defer
> +	 * doesn't make much sense.

Quite - so why not do the obvious and request these in the probe and hold
them until remove?  Then if they aren't ready defer the probe. This driver
is useless until the ADC is there so why let it successfully probe before
that point?

> +	 */
> +	st->chan_x = iio_channel_get(dev->dev.parent, "x");
> +	if (IS_ERR_OR_NULL(st->chan_x)) {
> +		dev_err(dev->dev.parent, "cannot get X channel from ADC");
> +		ret = PTR_ERR(st->chan_x);
> +		goto at91_rts_open_free_chan;
> +	}
> +
> +	st->chan_y = iio_channel_get(dev->dev.parent, "y");
> +	if (IS_ERR_OR_NULL(st->chan_y)) {
> +		dev_err(dev->dev.parent, "cannot get Y channel from ADC");
> +		ret = PTR_ERR(st->chan_y);
> +		goto at91_rts_open_free_chan;
> +	}
> +
> +	st->chan_pressure = iio_channel_get(dev->dev.parent, "pressure");
> +	if (IS_ERR_OR_NULL(st->chan_pressure)) {
> +		dev_err(dev->dev.parent, "cannot get pressure channel from ADC");
> +		ret = PTR_ERR(st->chan_pressure);
> +		goto at91_rts_open_free_chan;
> +	}
> +
> +	/* look for the trigger in device tree */
> +	st->trig = iio_trigger_find(dev->dev.parent, NULL);
> +	if (IS_ERR_OR_NULL(st->trig)) {
> +		dev_err(dev->dev.parent, "cannot get trigger from ADC");
> +		ret = PTR_ERR(st->trig)
This also feels like it should be retrieved during the probe and we should
defer if that fails.  Can't do anything useful without it!
> +		goto at91_rts_open_free_chan;
> +	}
> +
> +	/* allocate a pollfunc for the trigger */
> +	st->rts_pf = iio_alloc_pollfunc(at91_rts_trigger_handler, NULL,
> +					IRQF_ONESHOT, NULL,
> +					dev->dev.parent->of_node->name);
> +	if (!st->rts_pf) {
> +		ret = -ENOMEM;
> +		dev_err(dev->dev.parent, "cannot allocate trigger pollfunc");
> +		goto at91_rts_open_free_chan;
> +	}
> +
> +	iio_pollfunc_set_private_data(st->rts_pf, st);
> +
> +	/*
> +	 * Attach the pollfunc to the trigger. This will also call the
> +	 * configure function to enable the trigger
> +	 */
> +	ret = iio_trigger_attach_poll_func(st->trig, st->rts_pf);
> +	if (ret)
> +		goto at91_rts_open_dealloc_pf;
Ah. Now I think I see why you needed the poll function rather than 
doing this with a callback buffer.

I'd rather see a consumer interface that requests the whole ADC runs on
a particular trigger.

> +
> +	dev_dbg(dev->dev.parent, "channels found, attached to trigger");
> +
> +	st->adc_connected = true;
> +	return 0;
> +
> +at91_rts_open_dealloc_pf:
> +	iio_dealloc_pollfunc(st->rts_pf);
> +at91_rts_open_free_chan:
> +	if (!IS_ERR_OR_NULL(st->chan_x))
> +		iio_channel_release(st->chan_x);
> +	if (!IS_ERR_OR_NULL(st->chan_y))
> +		iio_channel_release(st->chan_y);
> +	if (!IS_ERR_OR_NULL(st->chan_pressure))
> +		iio_channel_release(st->chan_pressure);
> +	/*
> +	 * Avoid keeping old values in channel pointers. in case some channel
> +	 * failed and we reopen them, and now fail, we will have invalid values
> +	 * to release. So write them as NULL now.
> +	 */
> +	st->chan_x = NULL;
> +	st->chan_y = NULL;
> +	st->chan_pressure = NULL;
> +	return ret;
> +}
> +
> +static void at91_rts_close(struct input_dev *dev)
> +{
> +	struct at91_rts *st = input_get_drvdata(dev);
> +
> +	if (!st->adc_connected)
> +		return;
> +
> +	iio_trigger_detach_poll_func(st->trig, st->rts_pf);
> +	iio_dealloc_pollfunc(st->rts_pf);
> +
> +	if (!IS_ERR_OR_NULL(st->chan_x))
> +		iio_channel_release(st->chan_x);
> +	if (!IS_ERR_OR_NULL(st->chan_y))
> +		iio_channel_release(st->chan_y);
> +	if (!IS_ERR_OR_NULL(st->chan_pressure))
> +		iio_channel_release(st->chan_pressure);
> +
> +	st->adc_connected = false;
> +}
> +
> +static int at91_rts_probe(struct platform_device *pdev)
> +{
> +	int ret;
> +	struct at91_rts *st;
> +	struct input_dev *input;
> +	struct device *dev = &pdev->dev;
> +	struct device_node *node = dev->of_node;
> +
> +	st = devm_kzalloc(dev, sizeof(struct at91_rts), GFP_KERNEL);
> +	if (!st)
> +		return -ENOMEM;
> +	st->adc_connected = false;
> +
> +	INIT_WORK(&st->workq, at91_rts_workq_handler);
> +
> +	input = devm_input_allocate_device(dev);
> +	if (!input) {
> +		dev_err(dev, "failed to allocate input device\n");
> +		return -ENOMEM;
> +	}
> +
> +	ret = of_property_read_u32(node, "microchip,pressure-threshold",
> +				   &st->pressure_threshold);
> +	if (ret < 0) {
> +		dev_dbg(dev, "can't get touchscreen pressure threshold property.\n");
> +		st->pressure_threshold = AT91_RTS_DEFAULT_PRESSURE_THRESHOLD;
> +	}
> +
> +	input->name = DRIVER_NAME;
> +	input->id.bustype = BUS_HOST;
> +	input->dev.parent = &pdev->dev;
> +	input->open = at91_rts_open;
> +	input->close = at91_rts_close;
> +
> +	input_set_abs_params(input, ABS_X, 0, MAX_POS_MASK - 1, 0, 0);
> +	input_set_abs_params(input, ABS_Y, 0, MAX_POS_MASK, 0, 0);
> +	input_set_abs_params(input, ABS_PRESSURE, 0, 0xffffff, 0, 0);
> +
> +	input->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_ABS);
> +	input->keybit[BIT_WORD(BTN_TOUCH)] = BIT_MASK(BTN_TOUCH);
> +
> +	st->input = input;
> +	input_set_drvdata(input, st);
> +
> +	ret = input_register_device(input);
> +	if (ret) {
> +		dev_err(dev, "failed to register input device: %d", ret);
> +		return ret;
> +	}
> +
> +	platform_set_drvdata(pdev, st);
> +
> +	dev_info(dev, "probed successfully\n");

Not useful. There are many ways to find this out without looking at dmesg.
Please remove.

> +	return 0;
> +}
> +
> +static int at91_rts_remove(struct platform_device *pdev)
> +{
> +	struct at91_rts *st = platform_get_drvdata(pdev);
> +
> +	input_unregister_device(st->input);
> +
> +	return 0;
> +}
> +
> +static const struct of_device_id at91_rts_of_match[] = {
> +	{
> +		.compatible = "microchip,sama5d2-resistive-touch",
> +	}, {
> +		/* sentinel */
> +	},
> +};
> +MODULE_DEVICE_TABLE(of, at91_rts_of_match);
> +
> +static struct platform_driver atmel_rts_driver = {
> +	.probe = at91_rts_probe,
> +	.remove = at91_rts_remove,
> +	.driver = {
> +		   .name = DRIVER_NAME,
> +		   .of_match_table = of_match_ptr(at91_rts_of_match),
> +	},
> +};
> +
> +module_platform_driver(atmel_rts_driver);
> +
> +MODULE_AUTHOR("Eugen Hristev <eugen.hristev@xxxxxxxxxxxxx>");
> +MODULE_DESCRIPTION("Microchip SAMA5D2 Resistive Touch Driver");
> +MODULE_LICENSE("GPL v2");