Input: atmel_mxt_ts: Avoid excess read length on limited controllers
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Message ID 20200613145632.113573-1-marex@denx.de
State New
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Series
  • Input: atmel_mxt_ts: Avoid excess read length on limited controllers
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Commit Message

Marek Vasut June 13, 2020, 2:56 p.m. UTC
Some I2C controllers have a hard limit on the number of data they can
transfer in one transfer (e.g. Xilinx XIIC has 255 bytes). The Atmel
MXT touchscreen driver mxt_process_messages_until_invalid() function
can trigger a read much longer than that (e.g. 690 bytes in my case).
This transfer can however be easily split into multiple shorter ones,
esp. since the single T5 message is 10 bytes or so.

This patch adds a check for the quirk presence and if it is present,
limits the number of messages read out of the controller such that
they are below the quirk limit. This makes it possible for the MXT
driver to work even on such limited controllers.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Nick Dyer <nick@shmanahar.org>
Cc: Evan Green <evgreen@chromium.org>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Sasha Levin <sashal@kernel.org>
---
 drivers/input/touchscreen/atmel_mxt_ts.c | 30 ++++++++++++++++++------
 1 file changed, 23 insertions(+), 7 deletions(-)

Patch
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diff --git a/drivers/input/touchscreen/atmel_mxt_ts.c b/drivers/input/touchscreen/atmel_mxt_ts.c
index a2189739e30f5..faa3f3f987d46 100644
--- a/drivers/input/touchscreen/atmel_mxt_ts.c
+++ b/drivers/input/touchscreen/atmel_mxt_ts.c
@@ -985,21 +985,37 @@  static int mxt_proc_message(struct mxt_data *data, u8 *message)
 
 static int mxt_read_and_process_messages(struct mxt_data *data, u8 count)
 {
+	const struct i2c_adapter_quirks *q = data->client->adapter->quirks;
 	struct device *dev = &data->client->dev;
-	int ret;
-	int i;
+	int i, ret, offset = 0;
+	u16 rem, chunk = count, total = count;
 	u8 num_valid = 0;
 
 	/* Safety check for msg_buf */
 	if (count > data->max_reportid)
 		return -EINVAL;
 
+	/* Handle controller read-length limitations */
+	if (q && q->max_read_len) {
+		chunk = min((u16)(q->max_read_len / data->T5_msg_size),
+			    (u16)count);
+	}
+
 	/* Process remaining messages if necessary */
-	ret = __mxt_read_reg(data->client, data->T5_address,
-				data->T5_msg_size * count, data->msg_buf);
-	if (ret) {
-		dev_err(dev, "Failed to read %u messages (%d)\n", count, ret);
-		return ret;
+	while (total) {
+		rem = min(total, chunk);
+		ret = __mxt_read_reg(data->client, data->T5_address,
+				     data->T5_msg_size * rem,
+				     data->msg_buf +
+					(offset * data->T5_msg_size));
+		if (ret) {
+			dev_err(dev,
+				"Failed to read %u messages (offset %u of total %u) (%d)\n",
+				rem, offset, count, ret);
+			return ret;
+		}
+		total -= rem;
+		offset += rem;
 	}
 
 	for (i = 0;  i < count; i++) {