Input: ads7846 - be more compatible with the hwmon framework

 - Hook up to hwmon
     * show sensor attributes only if hwmon is present
     * ... and the board's reference voltage is known
     * otherwise be just a touchscreen
 - Report voltages per hwmon convention
     * measure in millivolts
     * voltages are named in[0-8]_input (ugh)
     * for 7846 chips, properly range-adjust vBATT/in1_input

Battery measurements help during recharge monitoring.  On OSK/Mistral,
the measured voltage agreed with a multimeter to several decimal places.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

2 files changed, 224 insertions, 91 deletions

diff --git a/drivers/input/touchscreen/Kconfig b/drivers/input/touchscreen/Kconfig
index 29ca0ab0acb..4bec8422821 100644
--- a/drivers/input/touchscreen/Kconfig
+++ b/drivers/input/touchscreen/Kconfig
@@ -12,13 +12,18 @@ menuconfig INPUT_TOUCHSCREEN
 if INPUT_TOUCHSCREEN
 
 config TOUCHSCREEN_ADS7846
-        tristate "ADS 7846 based touchscreens"
+        tristate "ADS 7846/7843 based touchscreens"
         depends on SPI_MASTER
+        depends on HWMON = n || HWMON
         help
           Say Y here if you have a touchscreen interface using the
-          ADS7846 controller, and your board-specific initialization
+          ADS7846 or ADS7843 controller, and your board-specific setup
           code includes that in its table of SPI devices.
 
+          If HWMON is selected, and the driver is told the reference voltage
+          on your board, you will also get hwmon interfaces for the voltage
+          (and on ads7846, temperature) sensors of this chip.
+
           If unsure, say N (but it's safe to say "Y").
 
           To compile this driver as a module, choose M here: the
diff --git a/drivers/input/touchscreen/ads7846.c b/drivers/input/touchscreen/ads7846.c
index b18c63a3f2a..cd251efda41 100644
--- a/drivers/input/touchscreen/ads7846.c
+++ b/drivers/input/touchscreen/ads7846.c
@@ -17,8 +17,9 @@
  *  it under the terms of the GNU General Public License version 2 as
  *  published by the Free Software Foundation.
  */
-#include <linux/device.h>
+#include <linux/hwmon.h>
 #include <linux/init.h>
+#include <linux/err.h>
 #include <linux/delay.h>
 #include <linux/input.h>
 #include <linux/interrupt.h>
@@ -69,7 +70,7 @@ struct ts_event {
         u16     x;
         u16     y;
         u16     z1, z2;
-        int    ignore;
+        int     ignore;
 };
 
 struct ads7846 {
@@ -77,7 +78,12 @@ struct ads7846 {
         char                    phys[32];
 
         struct spi_device       *spi;
+
+#if defined(CONFIG_HWMON) || defined(CONFIG_HWMON_MODULE)
         struct attribute_group  *attr_group;
+        struct class_device     *hwmon;
+#endif
+
         u16                     model;
         u16                     vref_delay_usecs;
         u16                     x_plate_ohms;
@@ -170,7 +176,12 @@ struct ads7846 {
 
 /*
  * Non-touchscreen sensors only use single-ended conversions.
+ * The range is GND..vREF. The ads7843 and ads7835 must use external vREF;
+ * ads7846 lets that pin be unconnected, to use internal vREF.
  */
+static unsigned vREF_mV;
+module_param(vREF_mV, uint, 0);
+MODULE_PARM_DESC(vREF_mV, "external vREF voltage, in milliVolts");
 
 struct ser_req {
         u8                      ref_on;
@@ -198,50 +209,55 @@ static int ads7846_read12_ser(struct device *dev, unsigned command)
         struct ser_req          *req = kzalloc(sizeof *req, GFP_KERNEL);
         int                     status;
         int                     sample;
-        int                     i;
+        int                     use_internal;
 
         if (!req)
                 return -ENOMEM;
 
         spi_message_init(&req->msg);
 
-        /* activate reference, so it has time to settle; */
-        req->ref_on = REF_ON;
-        req->xfer[0].tx_buf = &req->ref_on;
-        req->xfer[0].len = 1;
-        req->xfer[1].rx_buf = &req->scratch;
-        req->xfer[1].len = 2;
-
-        /*
-         * for external VREF, 0 usec (and assume it's always on);
-         * for 1uF, use 800 usec;
-         * no cap, 100 usec.
-         */
-        req->xfer[1].delay_usecs = ts->vref_delay_usecs;
+        /* FIXME boards with ads7846 might use external vref instead ... */
+        use_internal = (ts->model == 7846);
+
+        /* maybe turn on internal vREF, and let it settle */
+        if (use_internal) {
+                req->ref_on = REF_ON;
+                req->xfer[0].tx_buf = &req->ref_on;
+                req->xfer[0].len = 1;
+                spi_message_add_tail(&req->xfer[0], &req->msg);
+
+                req->xfer[1].rx_buf = &req->scratch;
+                req->xfer[1].len = 2;
+
+                /* for 1uF, settle for 800 usec; no cap, 100 usec.  */
+                req->xfer[1].delay_usecs = ts->vref_delay_usecs;
+                spi_message_add_tail(&req->xfer[1], &req->msg);
+        }
 
         /* take sample */
         req->command = (u8) command;
         req->xfer[2].tx_buf = &req->command;
         req->xfer[2].len = 1;
+        spi_message_add_tail(&req->xfer[2], &req->msg);
+
         req->xfer[3].rx_buf = &req->sample;
         req->xfer[3].len = 2;
+        spi_message_add_tail(&req->xfer[3], &req->msg);
 
         /* REVISIT:  take a few more samples, and compare ... */
 
-        /* turn off reference */
-        req->ref_off = REF_OFF;
-        req->xfer[4].tx_buf = &req->ref_off;
-        req->xfer[4].len = 1;
-        req->xfer[5].rx_buf = &req->scratch;
-        req->xfer[5].len = 2;
-
-        CS_CHANGE(req->xfer[5]);
-
-        /* group all the transfers together, so we can't interfere with
-         * reading touchscreen state; disable penirq while sampling
-         */
-        for (i = 0; i < 6; i++)
-                spi_message_add_tail(&req->xfer[i], &req->msg);
+        /* maybe off internal vREF */
+        if (use_internal) {
+                req->ref_off = REF_OFF;
+                req->xfer[4].tx_buf = &req->ref_off;
+                req->xfer[4].len = 1;
+                spi_message_add_tail(&req->xfer[4], &req->msg);
+
+                req->xfer[5].rx_buf = &req->scratch;
+                req->xfer[5].len = 2;
+                CS_CHANGE(req->xfer[5]);
+                spi_message_add_tail(&req->xfer[5], &req->msg);
+        }
 
         ts->irq_disabled = 1;
         disable_irq(spi->irq);
@@ -261,25 +277,173 @@ static int ads7846_read12_ser(struct device *dev, unsigned command)
         return status ? status : sample;
 }
 
-#define SHOW(name) static ssize_t \
+#if defined(CONFIG_HWMON) || defined(CONFIG_HWMON_MODULE)
+
+#define SHOW(name, var, adjust) static ssize_t \
 name ## _show(struct device *dev, struct device_attribute *attr, char *buf) \
 { \
+        struct ads7846 *ts = dev_get_drvdata(dev); \
         ssize_t v = ads7846_read12_ser(dev, \
-                        READ_12BIT_SER(name) | ADS_PD10_ALL_ON); \
+                        READ_12BIT_SER(var) | ADS_PD10_ALL_ON); \
         if (v < 0) \
                 return v; \
-        return sprintf(buf, "%u\n", (unsigned) v); \
+        return sprintf(buf, "%u\n", adjust(ts, v)); \
 } \
 static DEVICE_ATTR(name, S_IRUGO, name ## _show, NULL);
 
-SHOW(temp0)
-SHOW(temp1)
-SHOW(vaux)
-SHOW(vbatt)
+
+/* Sysfs conventions report temperatures in millidegrees Celcius.
+ * ADS7846 could use the low-accuracy two-sample scheme, but can't do the high
+ * accuracy scheme without calibration data.  For now we won't try either;
+ * userspace sees raw sensor values, and must scale/calibrate appropriately.
+ */
+static inline unsigned null_adjust(struct ads7846 *ts, ssize_t v)
+{
+        return v;
+}
+
+SHOW(temp0, temp0, null_adjust)         /* temp1_input */
+SHOW(temp1, temp1, null_adjust)         /* temp2_input */
+
+
+/* sysfs conventions report voltages in millivolts.  We can convert voltages
+ * if we know vREF.  userspace may need to scale vAUX to match the board's
+ * external resistors; we assume that vBATT only uses the internal ones.
+ */
+static inline unsigned vaux_adjust(struct ads7846 *ts, ssize_t v)
+{
+        unsigned retval = v;
+
+        /* external resistors may scale vAUX into 0..vREF */
+        retval *= vREF_mV;
+        retval = retval >> 12;
+        return retval;
+}
+
+static inline unsigned vbatt_adjust(struct ads7846 *ts, ssize_t v)
+{
+        unsigned retval = vaux_adjust(ts, v);
+
+        /* ads7846 has a resistor ladder to scale this signal down */
+        if (ts->model == 7846)
+                retval *= 4;
+        return retval;
+}
+
+SHOW(in0_input, vaux, vaux_adjust)
+SHOW(in1_input, vbatt, vbatt_adjust)
+
+
+static struct attribute *ads7846_attributes[] = {
+        &dev_attr_temp0.attr,
+        &dev_attr_temp1.attr,
+        &dev_attr_in0_input.attr,
+        &dev_attr_in1_input.attr,
+        NULL,
+};
+
+static struct attribute_group ads7846_attr_group = {
+        .attrs = ads7846_attributes,
+};
+
+static struct attribute *ads7843_attributes[] = {
+        &dev_attr_in0_input.attr,
+        &dev_attr_in1_input.attr,
+        NULL,
+};
+
+static struct attribute_group ads7843_attr_group = {
+        .attrs = ads7843_attributes,
+};
+
+static struct attribute *ads7845_attributes[] = {
+        &dev_attr_in0_input.attr,
+        NULL,
+};
+
+static struct attribute_group ads7845_attr_group = {
+        .attrs = ads7845_attributes,
+};
+
+static int ads784x_hwmon_register(struct spi_device *spi, struct ads7846 *ts)
+{
+        struct class_device *hwmon;
+        int err;
+
+        /* hwmon sensors need a reference voltage */
+        switch (ts->model) {
+        case 7846:
+                if (!vREF_mV) {
+                        dev_dbg(&spi->dev, "assuming 2.5V internal vREF\n");
+                        vREF_mV = 2500;
+                }
+                break;
+        case 7845:
+        case 7843:
+                if (!vREF_mV) {
+                        dev_warn(&spi->dev,
+                                "external vREF for ADS%d not specified\n",
+                                ts->model);
+                        return 0;
+                }
+                break;
+        }
+
+        /* different chips have different sensor groups */
+        switch (ts->model) {
+        case 7846:
+                ts->attr_group = &ads7846_attr_group;
+                break;
+        case 7845:
+                ts->attr_group = &ads7845_attr_group;
+                break;
+        case 7843:
+                ts->attr_group = &ads7843_attr_group;
+                break;
+        default:
+                dev_dbg(&spi->dev, "ADS%d not recognized\n", ts->model);
+                return 0;
+        }
+
+        err = sysfs_create_group(&spi->dev.kobj, ts->attr_group);
+        if (err)
+                return err;
+
+        hwmon = hwmon_device_register(&spi->dev);
+        if (IS_ERR(hwmon)) {
+                sysfs_remove_group(&spi->dev.kobj, ts->attr_group);
+                return PTR_ERR(hwmon);
+        }
+
+        ts->hwmon = hwmon;
+        return 0;
+}
+
+static void ads784x_hwmon_unregister(struct spi_device *spi,
+                                     struct ads7846 *ts)
+{
+        if (ts->hwmon) {
+                sysfs_remove_group(&spi->dev.kobj, ts->attr_group);
+                hwmon_device_unregister(ts->hwmon);
+        }
+}
+
+#else
+static inline int ads784x_hwmon_register(struct spi_device *spi,
+                                         struct ads7846 *ts)
+{
+        return 0;
+}
+
+static inline void ads784x_hwmon_unregister(struct spi_device *spi,
+                                            struct ads7846 *ts)
+{
+}
+#endif
 
 static int is_pen_down(struct device *dev)
 {
-        struct ads7846          *ts = dev_get_drvdata(dev);
+        struct ads7846  *ts = dev_get_drvdata(dev);
 
         return ts->pendown;
 }
@@ -323,46 +487,14 @@ static ssize_t ads7846_disable_store(struct device *dev,
 
 static DEVICE_ATTR(disable, 0664, ads7846_disable_show, ads7846_disable_store);
 
-static struct attribute *ads7846_attributes[] = {
-        &dev_attr_temp0.attr,
-        &dev_attr_temp1.attr,
-        &dev_attr_vbatt.attr,
-        &dev_attr_vaux.attr,
-        &dev_attr_pen_down.attr,
-        &dev_attr_disable.attr,
-        NULL,
-};
-
-static struct attribute_group ads7846_attr_group = {
-        .attrs = ads7846_attributes,
-};
-
-/*
- * ads7843/7845 don't have temperature sensors, and
- * use the other sensors a bit differently too
- */
-
-static struct attribute *ads7843_attributes[] = {
-        &dev_attr_vbatt.attr,
-        &dev_attr_vaux.attr,
+static struct attribute *ads784x_attributes[] = {
         &dev_attr_pen_down.attr,
         &dev_attr_disable.attr,
         NULL,
 };
 
-static struct attribute_group ads7843_attr_group = {
-        .attrs = ads7843_attributes,
-};
-
-static struct attribute *ads7845_attributes[] = {
-        &dev_attr_vaux.attr,
-        &dev_attr_pen_down.attr,
-        &dev_attr_disable.attr,
-        NULL,
-};
-
-static struct attribute_group ads7845_attr_group = {
-        .attrs = ads7845_attributes,
+static struct attribute_group ads784x_attr_group = {
+        .attrs = ads784x_attributes,
 };
 
 /*--------------------------------------------------------------------------*/
@@ -886,28 +1018,21 @@ static int __devinit ads7846_probe(struct spi_device *spi)
                 goto err_cleanup_filter;
         }
 
+        err = ads784x_hwmon_register(spi, ts);
+        if (err)
+                goto err_free_irq;
+
         dev_info(&spi->dev, "touchscreen, irq %d\n", spi->irq);
 
-        /* take a first sample, leaving nPENIRQ active; avoid
+        /* take a first sample, leaving nPENIRQ active and vREF off; avoid
          * the touchscreen, in case it's not connected.
          */
         (void) ads7846_read12_ser(&spi->dev,
                           READ_12BIT_SER(vaux) | ADS_PD10_ALL_ON);
 
-        switch (ts->model) {
-        case 7846:
-                ts->attr_group = &ads7846_attr_group;
-                break;
-        case 7845:
-                ts->attr_group = &ads7845_attr_group;
-                break;
-        default:
-                ts->attr_group = &ads7843_attr_group;
-                break;
-        }
-        err = sysfs_create_group(&spi->dev.kobj, ts->attr_group);
+        err = sysfs_create_group(&spi->dev.kobj, &ads784x_attr_group);
         if (err)
-                goto err_free_irq;
+                goto err_remove_hwmon;
 
         err = input_register_device(input_dev);
         if (err)
@@ -916,7 +1041,9 @@ static int __devinit ads7846_probe(struct spi_device *spi)
         return 0;
 
  err_remove_attr_group:
-        sysfs_remove_group(&spi->dev.kobj, ts->attr_group);
+        sysfs_remove_group(&spi->dev.kobj, &ads784x_attr_group);
+ err_remove_hwmon:
+        ads784x_hwmon_unregister(spi, ts);
  err_free_irq:
         free_irq(spi->irq, ts);
  err_cleanup_filter:
@@ -932,11 +1059,12 @@ static int __devexit ads7846_remove(struct spi_device *spi)
 {
         struct ads7846          *ts = dev_get_drvdata(&spi->dev);
 
+        ads784x_hwmon_unregister(spi, ts);
         input_unregister_device(ts->input);
 
         ads7846_suspend(spi, PMSG_SUSPEND);
 
-        sysfs_remove_group(&spi->dev.kobj, ts->attr_group);
+        sysfs_remove_group(&spi->dev.kobj, &ads784x_attr_group);
 
         free_irq(ts->spi->irq, ts);
         /* suspend left the IRQ disabled */