Input: atmel_mxt_ts - implement CRC check for configuration data

The configuration is stored in NVRAM on the maXTouch chip. When the device
is reset it reports a CRC of the stored configuration values. Therefore it
isn't necessary to send the configuration on each probe - we can check the
CRC matches and avoid a timeconsuming backup/reset cycle.

Signed-off-by: Nick Dyer <nick.dyer@itdev.co.uk>
Acked-by: Benson Leung <bleung@chromium.org>
Acked-by: Yufeng Shen <miletus@chromium.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/touchscreen/atmel_mxt_ts.c

@@ -188,6 +188,7 @@
 #define MXT_BACKUP_TIME		50	/* msec */
 #define MXT_RESET_TIME		200	/* msec */
 #define MXT_RESET_TIMEOUT	3000	/* msec */
+#define MXT_CRC_TIMEOUT		1000	/* msec */
 #define MXT_FW_RESET_TIME	3000	/* msec */
 #define MXT_FW_CHG_TIMEOUT	300	/* msec */
 
@@ -259,6 +260,7 @@ struct mxt_data {
 	unsigned int max_x;
 	unsigned int max_y;
 	bool in_bootloader;
+	u32 config_crc;
 
 	/* Cached parameters from object table */
 	u8 T6_reportid;
@@ -272,6 +274,9 @@ struct mxt_data {
 
 	/* for reset handling */
 	struct completion reset_completion;
+
+	/* for config update handling */
+	struct completion crc_completion;
 };
 
 static size_t mxt_obj_size(const struct mxt_object *obj)
@@ -636,7 +641,7 @@ static void mxt_input_touchevent(struct mxt_data *data,
 	}
 }
 
-static unsigned mxt_extract_T6_csum(const u8 *csum)
+static u16 mxt_extract_T6_csum(const u8 *csum)
 {
 	return csum[0] | (csum[1] << 8) | (csum[2] << 16);
 }
@@ -654,6 +659,7 @@ static irqreturn_t mxt_process_messages_until_invalid(struct mxt_data *data)
 	struct device *dev = &data->client->dev;
 	u8 reportid;
 	bool update_input = false;
+	u32 crc;
 
 	do {
 		if (mxt_read_message(data, &message)) {
@@ -665,9 +671,15 @@ static irqreturn_t mxt_process_messages_until_invalid(struct mxt_data *data)
 
 		if (reportid == data->T6_reportid) {
 			u8 status = payload[0];
-			unsigned csum = mxt_extract_T6_csum(&payload[1]);
+
+			crc = mxt_extract_T6_csum(&payload[1]);
+			if (crc != data->config_crc) {
+				data->config_crc = crc;
+				complete(&data->crc_completion);
+			}
+
 			dev_dbg(dev, "Status: %02x Config Checksum: %06x\n",
-				status, csum);
+				status, data->config_crc);
 
 			if (status & MXT_T6_STATUS_RESET)
 				complete(&data->reset_completion);
@@ -757,6 +769,24 @@ static int mxt_soft_reset(struct mxt_data *data)
 	return 0;
 }
 
+static void mxt_update_crc(struct mxt_data *data, u8 cmd, u8 value)
+{
+	/*
+	 * On failure, CRC is set to 0 and config will always be
+	 * downloaded.
+	 */
+	data->config_crc = 0;
+	reinit_completion(&data->crc_completion);
+
+	mxt_t6_command(data, cmd, value, true);
+
+	/*
+	 * Wait for crc message. On failure, CRC is set to 0 and config will
+	 * always be downloaded.
+	 */
+	mxt_wait_for_completion(data, &data->crc_completion, MXT_CRC_TIMEOUT);
+}
+
 static int mxt_check_reg_init(struct mxt_data *data)
 {
 	const struct mxt_platform_data *pdata = data->pdata;
@@ -771,6 +801,16 @@ static int mxt_check_reg_init(struct mxt_data *data)
 		return 0;
 	}
 
+	mxt_update_crc(data, MXT_COMMAND_REPORTALL, 1);
+
+	if (data->config_crc == pdata->config_crc) {
+		dev_info(dev, "Config CRC 0x%06X: OK\n", data->config_crc);
+		return 0;
+	}
+
+	dev_info(dev, "Config CRC 0x%06X: does not match 0x%06X\n",
+		 data->config_crc, pdata->config_crc);
+
 	for (i = 0; i < data->info.object_num; i++) {
 		object = data->object_table + i;
 
@@ -790,6 +830,14 @@ static int mxt_check_reg_init(struct mxt_data *data)
 		index += size;
 	}
 
+	mxt_update_crc(data, MXT_COMMAND_BACKUPNV, MXT_BACKUP_VALUE);
+
+	ret = mxt_soft_reset(data);
+	if (ret)
+		return ret;
+
+	dev_info(dev, "Config successfully updated\n");
+
 	return 0;
 }
 
@@ -929,11 +977,6 @@ static int mxt_initialize(struct mxt_data *data)
 		goto err_free_object_table;
 	}
 
-	error = mxt_t6_command(data, MXT_COMMAND_BACKUPNV,
-			       MXT_BACKUP_VALUE, false);
-	if (!error)
-		mxt_soft_reset(data);
-
 	/* Update matrix size at info struct */
 	error = mxt_read_reg(client, MXT_MATRIX_X_SIZE, &val);
 	if (error)
@@ -1263,6 +1306,7 @@ static int mxt_probe(struct i2c_client *client,
 
 	init_completion(&data->bl_completion);
 	init_completion(&data->reset_completion);
+	init_completion(&data->crc_completion);
 
 	mxt_calc_resolution(data);
 

include/linux/i2c/atmel_mxt_ts.h

@@ -29,6 +29,7 @@
 struct mxt_platform_data {
 	const u8 *config;
 	size_t config_length;
+	u32 config_crc;
 
 	unsigned int x_size;
 	unsigned int y_size;