Input: raydium_i2c_ts - use single i2c_transfer transaction when using RM_CMD_BANK_SWITCH

On an AMD chromebook, where the same I2C bus is shared by both Raydium
touchscreen and a trackpad device, it is observed that interleaving of
I2C messages when `raydium_i2c_read_message()` is called leads to the
Raydium touch IC reporting incorrect information. This is the sequence
that was observed to result in the above issue:

* I2C write to Raydium device for RM_CMD_BANK_SWITCH
* I2C write to trackpad device
* I2C read from trackpad device
* I2C write to Raydium device for setting address
* I2C read from Raydium device >>>> This provides incorrect
  information

This change adds a new helper function `raydium_i2c_xfer()` that
performs I2C transactions to the Raydium device. It uses the register
address to decide if RM_CMD_BANK_SWITCH header needs to be sent to the
device (i.e. if register address is greater than 255, then bank switch
header is sent before the rest of the transaction). Additionally, it
ensures that all the I2C operations performed as part of
`raydium_i2c_xfer()` are done as a single i2c_transfer. This
guarantees that no other transactions are initiated to any other
device on the same bus in between. Additionally,
`raydium_i2c_{send|read}*` functions are refactored to use this new
helper function.

Verified with the patch across multiple reboots (>100) that the
information reported by the Raydium  touchscreen device during probe
is correct.
Signed-off-by: Furquan Shaikh <furquan@google.com>
Link: https://lore.kernel.org/r/20200821024006.3399663-1-furquan@google.comSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/touchscreen/raydium_i2c_ts.c

@@ -51,6 +51,7 @@
 
 /* Touch relative info */
 #define RM_MAX_RETRIES		3
+#define RM_RETRY_DELAY_MS	20
 #define RM_MAX_TOUCH_NUM	10
 #define RM_BOOT_DELAY_MS	100
 
@@ -136,83 +137,82 @@ struct raydium_data {
 	bool wake_irq_enabled;
 };
 
-static int raydium_i2c_send(struct i2c_client *client,
-			    u8 addr, const void *data, size_t len)
+static int raydium_i2c_xfer(struct i2c_client *client,
+			    u32 addr, void *data, size_t len, bool is_read)
 {
-	u8 *buf;
-	int tries = 0;
-	int ret;
-
-	buf = kmalloc(len + 1, GFP_KERNEL);
-	if (!buf)
-		return -ENOMEM;
-
-	buf[0] = addr;
-	memcpy(buf + 1, data, len);
-
-	do {
-		ret = i2c_master_send(client, buf, len + 1);
-		if (likely(ret == len + 1))
-			break;
-
-		msleep(20);
-	} while (++tries < RM_MAX_RETRIES);
-
-	kfree(buf);
-
-	if (unlikely(ret != len + 1)) {
-		if (ret >= 0)
-			ret = -EIO;
-		dev_err(&client->dev, "%s failed: %d\n", __func__, ret);
-		return ret;
-	}
+	struct raydium_bank_switch_header {
+		u8 cmd;
+		__be32 be_addr;
+	} __packed header = {
+		.cmd = RM_CMD_BANK_SWITCH,
+		.be_addr = cpu_to_be32(addr),
+	};
 
-	return 0;
-}
+	u8 reg_addr = addr & 0xff;
 
-static int raydium_i2c_read(struct i2c_client *client,
-			    u8 addr, void *data, size_t len)
-{
 	struct i2c_msg xfer[] = {
+		{
+			.addr = client->addr,
+			.len = sizeof(header),
+			.buf = (u8 *)&header,
+		},
 		{
 			.addr = client->addr,
 			.len = 1,
-			.buf = &addr,
+			.buf = &reg_addr,
 		},
 		{
 			.addr = client->addr,
-			.flags = I2C_M_RD,
 			.len = len,
 			.buf = data,
+			.flags = is_read ? I2C_M_RD : 0,
 		}
 	};
+
+	/*
+	 * If address is greater than 255, then RM_CMD_BANK_SWITCH needs to be
+	 * sent first. Else, skip the header i.e. xfer[0].
+	 */
+	int xfer_start_idx = (addr > 0xff) ? 0 : 1;
+	size_t xfer_count = ARRAY_SIZE(xfer) - xfer_start_idx;
 	int ret;
 
-	ret = i2c_transfer(client->adapter, xfer, ARRAY_SIZE(xfer));
-	if (unlikely(ret != ARRAY_SIZE(xfer)))
-		return ret < 0 ? ret : -EIO;
+	ret = i2c_transfer(client->adapter, &xfer[xfer_start_idx], xfer_count);
+	if (likely(ret == xfer_count))
+		return 0;
+
+	return ret < 0 ? ret : -EIO;
+}
 
-	return 0;
+static int raydium_i2c_send(struct i2c_client *client,
+			    u32 addr, const void *data, size_t len)
+{
+	int tries = 0;
+	int error;
+
+	do {
+		error = raydium_i2c_xfer(client, addr, (void *)data, len,
+					 false);
+		if (likely(!error))
+			return 0;
+
+		msleep(RM_RETRY_DELAY_MS);
+	} while (++tries < RM_MAX_RETRIES);
+
+	dev_err(&client->dev, "%s failed: %d\n", __func__, error);
+	return error;
 }
 
-static int raydium_i2c_read_message(struct i2c_client *client,
-				    u32 addr, void *data, size_t len)
+static int raydium_i2c_read(struct i2c_client *client,
+			    u32 addr, void *data, size_t len)
 {
-	__be32 be_addr;
 	size_t xfer_len;
 	int error;
 
 	while (len) {
 		xfer_len = min_t(size_t, len, RM_MAX_READ_SIZE);
-
-		be_addr = cpu_to_be32(addr);
-
-		error = raydium_i2c_send(client, RM_CMD_BANK_SWITCH,
-					 &be_addr, sizeof(be_addr));
-		if (!error)
-			error = raydium_i2c_read(client, addr & 0xff,
-						 data, xfer_len);
-		if (error)
+		error = raydium_i2c_xfer(client, addr, data, xfer_len, true);
+		if (unlikely(error))
 			return error;
 
 		len -= xfer_len;
@@ -223,27 +223,13 @@ static int raydium_i2c_read_message(struct i2c_client *client,
 	return 0;
 }
 
-static int raydium_i2c_send_message(struct i2c_client *client,
-				    u32 addr, const void *data, size_t len)
-{
-	__be32 be_addr = cpu_to_be32(addr);
-	int error;
-
-	error = raydium_i2c_send(client, RM_CMD_BANK_SWITCH,
-				 &be_addr, sizeof(be_addr));
-	if (!error)
-		error = raydium_i2c_send(client, addr & 0xff, data, len);
-
-	return error;
-}
-
 static int raydium_i2c_sw_reset(struct i2c_client *client)
 {
 	const u8 soft_rst_cmd = 0x01;
 	int error;
 
-	error = raydium_i2c_send_message(client, RM_RESET_MSG_ADDR,
-					 &soft_rst_cmd, sizeof(soft_rst_cmd));
+	error = raydium_i2c_send(client, RM_RESET_MSG_ADDR, &soft_rst_cmd,
+				 sizeof(soft_rst_cmd));
 	if (error) {
 		dev_err(&client->dev, "software reset failed: %d\n", error);
 		return error;
@@ -295,9 +281,8 @@ static int raydium_i2c_query_ts_info(struct raydium_data *ts)
 		if (error)
 			continue;
 
-		error = raydium_i2c_read_message(client,
-						 le32_to_cpu(query_bank_addr),
-						 &ts->info, sizeof(ts->info));
+		error = raydium_i2c_read(client, le32_to_cpu(query_bank_addr),
+					 &ts->info, sizeof(ts->info));
 		if (error)
 			continue;
 
@@ -834,8 +819,8 @@ static irqreturn_t raydium_i2c_irq(int irq, void *_dev)
 	if (ts->boot_mode != RAYDIUM_TS_MAIN)
 		goto out;
 
-	error = raydium_i2c_read_message(ts->client, ts->data_bank_addr,
-					 ts->report_data, ts->pkg_size);
+	error = raydium_i2c_read(ts->client, ts->data_bank_addr,
+				 ts->report_data, ts->pkg_size);
 	if (error)
 		goto out;