[PATCH 18/20] Input: atmel_mxt_ts - read num messages, then all messages

[Daniel Kurtz <djkurtz@chromium.org>]

Implement the MXT DMA method of reading messages.
On an interrupt, the T44 report always contains the number of messages
pending to be read.  So, read 1 byte from T44 in 1 i2c transaction, then
read the N pending messages in a second transaction.

The end result is a much much faster read time for all pending messages.
Using 400kHz i2c, it is possible to read 10 pending messages (e.g. for 10
moving contatcts) in less than 2.8ms, which is well less than the typical
10-15ms update rate.

Note: There is a possible optimization here.  The T44 byte is guaranteed
to always be right before the T5 address.  Thus, it should be possible
to always fetch the T44 message count and the first message in a single
transaction.  This would eliminate the overhead of a second complete read
transaction for the case where there is only a single pending message.
(This is actually the most common case, for instance with just 1-contact
on the device touch surface). This optimization, however, is not done in
this patch.

Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
---
 drivers/input/touchscreen/atmel_mxt_ts.c |   92 ++++++++++++++++++++----------
 1 files changed, 61 insertions(+), 31 deletions(-)

diff --git a/drivers/input/touchscreen/atmel_mxt_ts.c b/drivers/input/touchscreen/atmel_mxt_ts.c
index 88a474e..dafc030 100644
--- a/drivers/input/touchscreen/atmel_mxt_ts.c
+++ b/drivers/input/touchscreen/atmel_mxt_ts.c
@@ -251,8 +251,10 @@ struct mxt_data {
 	unsigned int max_y;
 
 	/* Cached parameters from object table */
+	u16 T5_address;
 	u8 T9_reportid_min;
 	u8 T9_reportid_max;
+	u16 T44_address;
 };
 
 static bool mxt_object_readable(unsigned int type)
@@ -486,21 +488,6 @@ static int mxt_read_object(struct mxt_data *data, struct mxt_object *object,
 			    val);
 }
 
-static int mxt_read_message(struct mxt_data *data,
-				 struct mxt_message *message)
-{
-	struct mxt_object *object;
-	u16 reg;
-
-	object = mxt_get_object(data, MXT_GEN_MESSAGE_T5);
-	if (!object)
-		return -EINVAL;
-
-	reg = object->start_address;
-	return mxt_read_reg(data->client, reg, sizeof(struct mxt_message),
-			    message);
-}
-
 static int mxt_write_object(struct mxt_data *data,
 				 u8 type, u8 offset, u8 val)
 {
@@ -515,6 +502,19 @@ static int mxt_write_object(struct mxt_data *data,
 	return mxt_write_reg(data->client, reg + offset, 1, &val);
 }
 
+static int mxt_read_num_messages(struct mxt_data *data, u8 *count)
+{
+	/* TODO: Optimization: read first message along with message count */
+	return mxt_read_reg(data->client, data->T44_address, 1, count);
+}
+
+static int mxt_read_messages(struct mxt_data *data, u8 count,
+			     struct mxt_message *messages)
+{
+	return mxt_read_reg(data->client, data->T5_address,
+			    sizeof(struct mxt_message) * count, messages);
+}
+
 static void mxt_input_touchevent(struct mxt_data *data,
 				 struct mxt_message *message)
 {
@@ -575,26 +575,50 @@ static void mxt_input_touchevent(struct mxt_data *data,
 	input_sync(input_dev);
 }
 
-static irqreturn_t mxt_interrupt(int irq, void *dev_id)
+static int mxt_proc_messages(struct mxt_data *data, u8 count)
 {
-	struct mxt_data *data = dev_id;
-	struct mxt_message message;
 	struct device *dev = &data->client->dev;
+	struct mxt_message messages[count], *msg;
+	int ret;
 
-	do {
-		if (mxt_read_message(data, &message)) {
-			dev_err(dev, "Failed to read message\n");
-			goto end;
-		}
+	ret = mxt_read_messages(data, count, messages);
+	if (ret) {
+		dev_err(dev, "Failed to read %u messages (%d).\n", count, ret);
+		return ret;
+	}
+
+	for (msg = messages; msg < &messages[count]; msg++) {
+		mxt_dump_message(dev, msg);
+
+		if (msg->reportid >= data->T9_reportid_min &&
+		    msg->reportid <= data->T9_reportid_max)
+			mxt_input_touchevent(data, msg);
+	}
+
+	return 0;
+}
+
+static int mxt_handle_messages(struct mxt_data *data)
+{
+	struct device *dev = &data->client->dev;
+	int ret;
+	u8 count;
 
-		if (message.reportid >= data->T9_reportid_min &&
-		    message.reportid <= data->T9_reportid_max)
-			mxt_input_touchevent(data, &message);
-		else
-			mxt_dump_message(dev, &message);
-	} while (message.reportid != 0xff);
+	ret = mxt_read_num_messages(data, &count);
+	if (ret) {
+		dev_err(dev, "Failed to read message count (%d).\n", ret);
+		return ret;
+	}
 
-end:
+	if (count > 0)
+		ret = mxt_proc_messages(data, count);
+
+	return ret;
+}
+
+static irqreturn_t mxt_interrupt(int irq, void *dev_id)
+{
+	mxt_handle_messages(dev_id);
 	return IRQ_HANDLED;
 }
 
@@ -642,7 +666,7 @@ static int mxt_make_highchg(struct mxt_data *data)
 
 	/* Read dummy message to make high CHG pin */
 	do {
-		error = mxt_read_message(data, &message);
+		error = mxt_read_messages(data, 1, &message);
 		if (error)
 			return error;
 	} while (message.reportid != 0xff && --count);
@@ -743,11 +767,17 @@ static int mxt_get_object_table(struct mxt_data *data)
 
 		/* Save data for objects used when processing interrupts */
 		switch (object->type) {
+		case MXT_GEN_MESSAGE_T5:
+			data->T5_address = object->start_address;
+			break;
 		case MXT_TOUCH_MULTI_T9:
 			data->T9_reportid_max = object->max_reportid;
 			data->T9_reportid_min = data->T9_reportid_max -
 						object->num_report_ids + 1;
 			break;
+		case MXT_SPT_MESSAGECOUNT_T44:
+			data->T44_address = object->start_address;
+			break;
 		}
 	}
 
-- 
1.7.7.3