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Date:	Sun, 20 Jul 2014 13:28:42 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Jonathan Cameron <jic23@...nel.org>
Cc:	Arnd Bergmann <arnd@...db.de>,
	linux-arm-kernel@...ts.infradead.org,
	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>,
	linux-input <linux-input@...r.kernel.org>
Subject: Re: [PATCH 2/2] iio: exynos-adc: add experimental touchscreen support

On Sun, Jul 20, 2014 at 02:51:37PM +0100, Jonathan Cameron wrote:
> On 20/07/14 14:49, Jonathan Cameron wrote:
> >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,
> Cc'd linux-input and Dmitry.
> >
> >>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);

It would be nice to actually close the device even if someone is
touching screen. Please implement open/close methods and have them set a
flag that you would check here.


> >>+
> >>+    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;

You do not need to fill these entries with fake data.

> >>+    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);

Are we sure that device is quiesced here and interrupt won't arrive
between input_unregister_device() and free_irq()? I guess if you
properly implement open/close it won't matter.

> >>+    }
> >>+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);

Should be unregister, not free.

> >>      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);
> >>

Thanks.

-- 
Dmitry
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