Input: ads7846 - add support for the ads7843 touchscreen

The ads7843 support has now become almost trivial since the last
rework.
Signed-off-by: Nicolas Ferre <nicolas.ferre@rfo.atmel.com>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

drivers/input/touchscreen/ads7846.c

@@ -39,7 +39,8 @@
 /*
  * 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.
+ * Support for ads7843 tested on Atmel at91sam926x-EK.
+ * Support for ads7845 has only been stubbed in.
  *
  * IRQ handling needs a workaround because of a shortcoming in handling
  * edge triggered IRQs on some platforms like the OMAP1/2. These
@@ -246,9 +247,8 @@ static int ads7846_read12_ser(struct device *dev, unsigned command)
 
 	/* REVISIT:  take a few more samples, and compare ... */
 
-	/* maybe off internal vREF */
-	if (use_internal) {
-		req->ref_off = REF_OFF;
+	/* converter in low power mode & enable PENIRQ */
+	req->ref_off = PWRDOWN;
 	req->xfer[4].tx_buf = &req->ref_off;
 	req->xfer[4].len = 1;
 	spi_message_add_tail(&req->xfer[4], &req->msg);
@@ -257,7 +257,6 @@ static int ads7846_read12_ser(struct device *dev, unsigned command)
 	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);
@@ -536,6 +535,9 @@ static void ads7846_rx(void *ads)
 	} else
 		Rt = 0;
 
+	if (ts->model == 7843)
+		Rt = ts->pressure_max / 2;
+
 	/* Sample found inconsistent by debouncing or pressure is beyond
 	 * the maximum. Don't report it to user space, repeat at least
 	 * once more the measurement