[PATCH] ads7846 conversion accuracy

This improves accuracy of the touchscreen and hwmon sensor readings,
addressing an issue noted by Imre Deak: there's an extra bit written before
the sample (12 bits) gets written out.

It also catches up to various comments, and makes the /proc/interrupts
entry sensible again.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: Imre Deak <imre.deak@nokia.com>
Cc: Jean Delvare <khali@linux-fr.org>
Cc: Dmitry Torokhov <dtor_core@ameritech.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 28 insertions, 25 deletions

diff --git a/drivers/input/touchscreen/ads7846.c b/drivers/input/touchscreen/ads7846.c
index 1494175ac6fe..161afddd0f44 100644
--- a/drivers/input/touchscreen/ads7846.c
+++ b/drivers/input/touchscreen/ads7846.c
@@ -36,13 +36,10 @@
 
 
 /*
- * This code has been tested on an ads7846 / N770 device.
+ * This code has been heavily tested on a Nokia 770, and lightly
+ * tested on other ads7846 devices (OSK/Mistral, Lubbock).
  * Support for ads7843 and ads7845 has only been stubbed in.
  *
- * Not yet done:  How accurate are the temperature and voltage
- * readings? (System-specific calibration should support
- * accuracy of 0.3 degrees C; otherwise it's 2.0 degrees.)
- *
  * IRQ handling needs a workaround because of a shortcoming in handling
  * edge triggered IRQs on some platforms like the OMAP1/2. These
  * platforms don't handle the ARM lazy IRQ disabling properly, thus we
@@ -248,10 +245,13 @@ static int ads7846_read12_ser(struct device *dev, unsigned command)
 
         if (req->msg.status)
                 status = req->msg.status;
+
+        /* on-wire is a must-ignore bit, a BE12 value, then padding */
         sample = be16_to_cpu(req->sample);
-        sample = sample >> 4;
-        kfree(req);
+        sample = sample >> 3;
+        sample &= 0x0fff;
 
+        kfree(req);
         return status ? status : sample;
 }
 
@@ -336,13 +336,13 @@ static void ads7846_rx(void *ads)
         u16                     x, y, z1, z2;
         unsigned long           flags;
 
-        /* adjust:  12 bit samples (left aligned), built from
-         * two 8 bit values writen msb-first.
+        /* adjust:  on-wire is a must-ignore bit, a BE12 value, then padding;
+         * built from two 8 bit values written msb-first.
          */
-        x = be16_to_cpu(ts->tc.x) >> 4;
-        y = be16_to_cpu(ts->tc.y) >> 4;
-        z1 = be16_to_cpu(ts->tc.z1) >> 4;
-        z2 = be16_to_cpu(ts->tc.z2) >> 4;
+        x = (be16_to_cpu(ts->tc.x) >> 3) & 0x0fff;
+        y = (be16_to_cpu(ts->tc.y) >> 3) & 0x0fff;
+        z1 = (be16_to_cpu(ts->tc.z1) >> 3) & 0x0fff;
+        z2 = (be16_to_cpu(ts->tc.z2) >> 3) & 0x0fff;
 
         /* range filtering */
         if (x == MAX_12BIT)
@@ -420,7 +420,7 @@ static void ads7846_debounce(void *ads)
 
         m = &ts->msg[ts->msg_idx];
         t = list_entry(m->transfers.prev, struct spi_transfer, transfer_list);
-        val = (*(u16 *)t->rx_buf) >> 3;
+        val = (be16_to_cpu(*(__be16 *)t->rx_buf) >> 3) & 0x0fff;
         if (!ts->read_cnt || (abs(ts->last_read - val) > ts->debounce_tol)) {
                 /* Repeat it, if this was the first read or the read
                  * wasn't consistent enough. */
@@ -469,7 +469,7 @@ static void ads7846_timer(unsigned long handle)
         spin_lock_irq(&ts->lock);
 
         if (unlikely(ts->msg_idx && !ts->pendown)) {
-                /* measurment cycle ended */
+                /* measurement cycle ended */
                 if (!device_suspended(&ts->spi->dev)) {
                         ts->irq_disabled = 0;
                         enable_irq(ts->spi->irq);
@@ -495,11 +495,10 @@ static irqreturn_t ads7846_irq(int irq, void *handle, struct pt_regs *regs)
         spin_lock_irqsave(&ts->lock, flags);
         if (likely(ts->get_pendown_state())) {
                 if (!ts->irq_disabled) {
-                        /* REVISIT irq logic for many ARM chips has cloned a
-                         * bug wherein disabling an irq in its handler won't
-                         * work;(it's disabled lazily, and too late to work.
-                         * until all their irq logic is fixed, we must shadow
-                         * that state here.
+                        /* The ARM do_simple_IRQ() dispatcher doesn't act
+                         * like the other dispatchers:  it will report IRQs
+                         * even after they've been disabled.  We work around
+                         * that here.  (The "generic irq" framework may help...)
                          */
                         ts->irq_disabled = 1;
                         disable_irq(ts->spi->irq);
@@ -609,16 +608,20 @@ static int __devinit ads7846_probe(struct spi_device *spi)
                 return -EINVAL;
         }
 
+        /* REVISIT when the irq can be triggered active-low, or if for some
+         * reason the touchscreen isn't hooked up, we don't need to access
+         * the pendown state.
+         */
         if (pdata->get_pendown_state == NULL) {
                 dev_dbg(&spi->dev, "no get_pendown_state function?\n");
                 return -EINVAL;
         }
 
-        /* We'd set the wordsize to 12 bits ... except that some controllers
-         * will then treat the 8 bit command words as 12 bits (and drop the
-         * four MSBs of the 12 bit result).  Result: inputs must be shifted
-         * to discard the four garbage LSBs.
+        /* We'd set TX wordsize 8 bits and RX wordsize to 13 bits ... except
+         * that even if the hardware can do that, the SPI controller driver
+         * may not.  So we stick to very-portable 8 bit words, both RX and TX.
          */
+        spi->bits_per_word = 8;
 
         ts = kzalloc(sizeof(struct ads7846), GFP_KERNEL);
         input_dev = input_allocate_device();
@@ -772,7 +775,7 @@ static int __devinit ads7846_probe(struct spi_device *spi)
 
         if (request_irq(spi->irq, ads7846_irq,
                         SA_SAMPLE_RANDOM | SA_TRIGGER_FALLING,
-                        spi->dev.bus_id, ts)) {
+                        spi->dev.driver->name, ts)) {
                 dev_dbg(&spi->dev, "irq %d busy?\n", spi->irq);
                 err = -EBUSY;
                 goto err_free_mem;