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Date:	Sun, 20 Jul 2014 14:49:10 +0100
From:	Jonathan Cameron <jic23@...nel.org>
To:	Arnd Bergmann <arnd@...db.de>, linux-arm-kernel@...ts.infradead.org
CC:	Chanwoo Choi <cw00.choi@...sung.com>, ch.naveen@...sung.com,
	mark.rutland@....com, devicetree@...r.kernel.org,
	kgene.kim@...sung.com, pawel.moll@....com,
	ijc+devicetree@...lion.org.uk, linux-iio@...r.kernel.org,
	t.figa@...sung.com, rdunlap@...radead.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-samsung-soc@...r.kernel.org, kyungmin.park@...sung.com,
	robh+dt@...nel.org, galak@...eaurora.org, heiko.stuebner@...com,
	Ben Dooks <ben-linux@...ff.org>
Subject: Re: [PATCH 2/2] iio: exynos-adc: add experimental touchscreen support

On 18/07/14 20:29, Arnd Bergmann wrote:
> This adds support for the touchscreen on Samsung s3c64xx.
> The driver is completely untested but shows roughly how
> it could be done, following the example of the at91 driver.
>
Hi Arnd,

> Open questions include:
>
> - compared to the old plat-samsung/adc driver, there is
>    no support for prioritizing ts over other clients, nor
>    for oversampling. From my reading of the code, the
>    priorities didn't actually have any effect at all, but
>    the oversampling might be needed. Maybe the original
>    authors have some insight.
>
> - I simply register the input device from the adc driver
>    itself, as the at91 code does. The driver also supports
>    sub-nodes, but I don't understand how they are meant
>    to be used, so using those might be better.
So, the alternative you are (I think) referring to is to use
the buffered in kernel client interface.  That way a separate
touch screen driver can use the output channels provided by IIO
in much the same way you might use a regulator or similar.
Note that whilst this is similar to the simple polled interface
used for things like the iio_hwmon driver, the data flow is
quite different (clearly the polled interfce would be
inappropriate here).

Whilst we've discussed it in the past for touch screen drivers
like this, usually the hardware isn't generic enough to be
of any real use if not being used as a touch screen.  As such
it's often simpler to just have the support directly in the
driver (as you've observed the at91 driver does this).

Whilst the interface has been there a while, it's not really had
all that much use.  The original target was the simpler case
of 3D accelerometer where we have a generic iio to input
bridge driver. Time constraints meant that I haven't yet actually
formally submitted the input side of this. Whilst there are lots
of other things that can use this interface, right now nothing
actually does so.

>
> - The new exynos_read_s3c64xx_ts() function is intentionally
>    very similar to the existing exynos_read_raw() functions.
>    It should probably be changed, either by merging the two
>    into one, or by simplifying the exynos_read_s3c64xx_ts()
>    function. This depends a bit on the answers to the questions
>    above.
I'd be tempted to not bother keeping them that similar.  It's
not a generic IIO channel so simplify it where possible.
>
> - We probably need to add support for platform_data as well,
>    I've skipped this so far.
>
> - Is anybody able to debug this driver on real hardware?
>    While it's possible that it actually works, it's more
>    likely that I made a few subtle mistakes.
>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
Looks pretty good to me.  A few symantic bits and pieces and
one bug spotted.  Short and sweet.
>
> diff --git a/Documentation/devicetree/bindings/arm/samsung/exynos-adc.txt b/Documentation/devicetree/bindings/arm/samsung/exynos-adc.txt
> index e1b74828f413..4329bf3c3326 100644
> --- a/Documentation/devicetree/bindings/arm/samsung/exynos-adc.txt
> +++ b/Documentation/devicetree/bindings/arm/samsung/exynos-adc.txt
> @@ -41,6 +41,10 @@ Required properties:
>   				       and compatible ADC block)
>   - vdd-supply		VDD input supply.
>
> +Optional properties:
> +- has-touchscreen:	If present, indicates that a touchscreen is
> +			connected an usable.
> +
>   Note: child nodes can be added for auto probing from device tree.
>
>   Example: adding device info in dtsi file
> diff --git a/drivers/iio/adc/exynos_adc.c b/drivers/iio/adc/exynos_adc.c
> index 5f95638513d2..cf1d9f3e2492 100644
> --- a/drivers/iio/adc/exynos_adc.c
> +++ b/drivers/iio/adc/exynos_adc.c
> @@ -34,6 +34,7 @@
>   #include <linux/regulator/consumer.h>
>   #include <linux/of_platform.h>
>   #include <linux/err.h>
> +#include <linux/input.h>
Might want to make the input side optional at compile time...
I supose the existing parts are unlikely to be used much in headless
devices, but you never know.  Maybe we just leave this until someone
shouts they want to be able to avoid compiling it in.
>
>   #include <linux/iio/iio.h>
>   #include <linux/iio/machine.h>
> @@ -103,6 +104,7 @@
>
>   /* Bit definitions common for ADC_V1 and ADC_V2 */
>   #define ADC_CON_EN_START	(1u << 0)
> +#define ADC_DATX_PRESSED	(1u << 15)
>   #define ADC_DATX_MASK		0xFFF
>
>   #define EXYNOS_ADC_TIMEOUT	(msecs_to_jiffies(100))
> @@ -110,16 +112,20 @@
>   struct exynos_adc {
>   	struct exynos_adc_data	*data;
>   	struct device		*dev;
> +	struct input_dev	*input;
>   	void __iomem		*regs;
>   	void __iomem		*enable_reg;
>   	struct clk		*clk;
>   	struct clk		*sclk;
>   	unsigned int		irq;
> +	unsigned int		tsirq;
>   	struct regulator	*vdd;
>
>   	struct completion	completion;
>
> +	bool			read_ts;
>   	u32			value;
> +	u32			value2;
As I state further down, I'd rather keep a little
clear of the naming used in IIO for bits that aren't
going through IIO (less confusing!). Maybe just
have
	u32 x, y;
>   	unsigned int            version;
>   };
>
> @@ -390,12 +396,61 @@ static int exynos_read_raw(struct iio_dev *indio_dev,
>   	return ret;
>   }
>
> +static int exynos_read_s3c64xx_ts(struct iio_dev *indio_dev,
> +				struct iio_chan_spec const *chan,
> +				int *val,
> +				int *val2,
> +				long mask)
> +{
> +	struct exynos_adc *info = iio_priv(indio_dev);
> +	unsigned long timeout;
> +	int ret;
> +
> +	if (mask != IIO_CHAN_INFO_RAW)
> +		return -EINVAL;
> +
> +	mutex_lock(&indio_dev->mlock);
> +	info->read_ts = 1;
> +
> +	reinit_completion(&info->completion);
> +
> +	writel(ADC_S3C2410_TSC_PULL_UP_DISABLE | ADC_TSC_AUTOPST,
> +	       ADC_V1_TSC(info->regs));
> +
> +	/* Select the ts channel to be used and Trigger conversion */
> +	info->data->start_conv(info, 0);
0 is a rather magic value.  A define perhaps?
> +
> +	timeout = wait_for_completion_timeout
> +			(&info->completion, EXYNOS_ADC_TIMEOUT);
> +	if (timeout == 0) {
> +		dev_warn(&indio_dev->dev, "Conversion timed out! Resetting\n");
> +		if (info->data->init_hw)
> +			info->data->init_hw(info);
> +		ret = -ETIMEDOUT;
> +	} else {
> +		*val = info->value;
> +		*val2 = info->value2;
This is definitely abuse as those two values are not intended for
different values.  If you want to do this please use different naming
and don't try to fiddle it into the IIO read raw framework.
As you've suggested above, better to simplify this code and drop the
bits cloned from the other handler.
> +		ret = IIO_VAL_INT;
> +	}
> +
> +	info->read_ts = 0;
> +	mutex_unlock(&indio_dev->mlock);
> +
> +	return ret;
> +}
> +
>   static irqreturn_t exynos_adc_isr(int irq, void *dev_id)
>   {
>   	struct exynos_adc *info = (struct exynos_adc *)dev_id;
>
>   	/* Read value */
> -	info->value = readl(ADC_V1_DATX(info->regs)) & ADC_DATX_MASK;
> +	if (info->read_ts) {
> +		info->value = readl(ADC_V1_DATX(info->regs)) & ADC_DATX_MASK;
> +		info->value2 = readl(ADC_V1_DATY(info->regs)) & ADC_DATX_MASK;
ADC_DATY_MASK would be more obviously correct.

> +		writel(ADC_TSC_WAIT4INT | ADC_S3C2443_TSC_UD_SEN, ADC_V1_TSC(info->regs));
Perhaps the above is cryptic enough to warrant a comment?
> +	} else {
> +		info->value = readl(ADC_V1_DATX(info->regs)) & ADC_DATX_MASK;
> +	}
>
>   	/* clear irq */
>   	if (info->data->clear_irq)
> @@ -406,6 +461,46 @@ static irqreturn_t exynos_adc_isr(int irq, void *dev_id)
>   	return IRQ_HANDLED;
>   }
>
> +/*
> + * Here we (ab)use a threaded interrupt handler to stay running
> + * for as long as the touchscreen remains pressed, we report
> + * a new event with the latest data and then sleep until the
> + * next timer tick. This mirrors the behavior of the old
> + * driver, with much less code.
> + */
> +static irqreturn_t exynos_ts_isr(int irq, void *dev_id)
> +{
> +	struct exynos_adc *info = dev_id;
> +	struct iio_dev *dev = dev_get_drvdata(info->dev);
> +	u32 x, y;
> +	bool pressed;
> +	int ret;
> +
> +	do {
> +		ret =exynos_read_s3c64xx_ts(dev, NULL, &x, &y, IIO_CHAN_INFO_RAW);
= exynos
> +		if (ret == -ETIMEDOUT)
> +			break;
> +
> +		pressed = x & y & ADC_DATX_PRESSED;
> +		if (!pressed)
> +			break;
> +
> +		input_report_abs(info->input, ABS_X, x & ADC_DATX_MASK);
> +		input_report_abs(info->input, ABS_Y, y & ADC_DATX_MASK);
> +		input_report_key(info->input, BTN_TOUCH, 1);
> +		input_sync(info->input);
> +
> +		msleep(1);
> +	} while (1);
> +
> +	input_report_key(info->input, BTN_TOUCH, 0);
> +	input_sync(info->input);
> +
> +	writel(0, ADC_V1_CLRINTPNDNUP(info->regs));
> +
> +	return IRQ_HANDLED;
> +}
> +
>   static int exynos_adc_reg_access(struct iio_dev *indio_dev,
>   			      unsigned reg, unsigned writeval,
>   			      unsigned *readval)
> @@ -457,12 +552,57 @@ static int exynos_adc_remove_devices(struct device *dev, void *c)
>   	return 0;
>   }
>
> +static int exynos_adc_ts_init(struct exynos_adc *info)
> +{
> +	int ret;
> +
> +	info->input = input_allocate_device();
> +	if (!info->input)
> +		return -ENOMEM;
> +
> +	info->input->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_ABS);
> +	info->input->keybit[BIT_WORD(BTN_TOUCH)] = BIT_MASK(BTN_TOUCH);
> +
> +	input_set_abs_params(info->input, ABS_X, 0, 0x3FF, 0, 0);
> +	input_set_abs_params(info->input, ABS_Y, 0, 0x3FF, 0, 0);
> +
> +	/* data from s3c2410_ts driver */
> +	info->input->name = "S3C24xx TouchScreen";
> +	info->input->id.bustype = BUS_HOST;
> +	info->input->id.vendor = 0xDEAD;
> +	info->input->id.product = 0xBEEF;
> +	info->input->id.version = 0x0200;
> +
> +	ret = input_register_device(info->input);
> +	if (ret) {
> +		input_free_device(info->input);
> +		goto err;
> +	}
> +
> +	if (info->tsirq > 0)
> +		ret = request_threaded_irq(info->irq, NULL, exynos_ts_isr,
> +					0, "touchscreen", info);
info->tsirq
(that had me really confused for a moment ;)
Also, perhaps a more specific name.  touchscreen_updown or similar as the
main interrupt is also used during touchscreen operation.
> +	if (ret < 0) {
> +		dev_err(info->dev, "failed requesting touchsccreen irq, irq = %d\n",
> +							info->irq);
> +		goto err_input;
> +	}
> +
> +	return 0;
> +
> +err_input:
> +	input_unregister_device(info->input);
> +err:
> +	return ret;
> +}
> +
>   static int exynos_adc_probe(struct platform_device *pdev)
>   {
>   	struct exynos_adc *info = NULL;
>   	struct device_node *np = pdev->dev.of_node;
>   	struct iio_dev *indio_dev = NULL;
>   	struct resource	*mem;
> +	bool has_ts;
>   	int ret = -ENODEV;
>   	int irq;
>
> @@ -498,8 +638,14 @@ static int exynos_adc_probe(struct platform_device *pdev)
>   		dev_err(&pdev->dev, "no irq resource?\n");
>   		return irq;
>   	}
> -
>   	info->irq = irq;
> +
> +	irq = platform_get_irq(pdev, 1);
> +	if (irq == -EPROBE_DEFER)
> +		return irq;
> +
> +	info->tsirq = irq;
> +
>   	info->dev = &pdev->dev;
>
>   	init_completion(&info->completion);
> @@ -565,6 +711,12 @@ static int exynos_adc_probe(struct platform_device *pdev)
>   	if (info->data->init_hw)
>   		info->data->init_hw(info);
>
> +	has_ts = of_property_read_bool(pdev->dev.of_node, "has-touchscreen");
> +	if (has_ts)
> +		ret = exynos_adc_ts_init(info);
> +	if (ret)
> +		goto err_iio;
> +
>   	ret = of_platform_populate(np, exynos_adc_match, NULL, &indio_dev->dev);
>   	if (ret < 0) {
>   		dev_err(&pdev->dev, "failed adding child nodes\n");
> @@ -576,6 +728,11 @@ static int exynos_adc_probe(struct platform_device *pdev)
>   err_of_populate:
>   	device_for_each_child(&indio_dev->dev, NULL,
>   				exynos_adc_remove_devices);
> +	if (has_ts) {
> +		input_unregister_device(info->input);
> +		free_irq(info->tsirq, info);
> +	}
> +err_iio:
>   	iio_device_unregister(indio_dev);
>   err_irq:
>   	free_irq(info->irq, info);
> @@ -595,9 +752,12 @@ static int exynos_adc_remove(struct platform_device *pdev)
>   	struct iio_dev *indio_dev = platform_get_drvdata(pdev);
>   	struct exynos_adc *info = iio_priv(indio_dev);
>
> +	input_free_device(info->input);	
>   	device_for_each_child(&indio_dev->dev, NULL,
>   				exynos_adc_remove_devices);
>   	iio_device_unregister(indio_dev);
> +	if (info->tsirq > 0)
> +		free_irq(info->tsirq, info);
>   	free_irq(info->irq, info);
>   	if (info->data->exit_hw)
>   		info->data->exit_hw(info);
>

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