[PATCH] i2c: slave-eeprom: add latch mode

[Jian Zhang]

The read operation is locked by byte, while the write operation is
locked by block (or based on the amount of data written). If we need to
ensure the integrity of a "block" of data that the other end can read,
then we need a latch mode, lock the buffer when a read operation is
requested.

Signed-off-by: Jian Zhang <zhangjian.3032@xxxxxxxxxxxxx>
---
 drivers/i2c/i2c-slave-eeprom.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/drivers/i2c/i2c-slave-eeprom.c b/drivers/i2c/i2c-slave-eeprom.c
index 5946c0d0aef9..29246ac7d350 100644
--- a/drivers/i2c/i2c-slave-eeprom.c
+++ b/drivers/i2c/i2c-slave-eeprom.c
@@ -33,7 +33,9 @@ struct eeprom_data {
 	u16 address_mask;
 	u8 num_address_bytes;
 	u8 idx_write_cnt;
+	bool latch;
 	bool read_only;
+	u8 *buffer_latch;
 	u8 buffer[];
 };
 
@@ -49,6 +51,11 @@ static int i2c_slave_eeprom_slave_cb(struct i2c_client *client,
 
 	switch (event) {
 	case I2C_SLAVE_WRITE_RECEIVED:
+		if (eeprom->latch) {
+			spin_lock(&eeprom->buffer_lock);
+			memcpy(eeprom->buffer_latch, eeprom->buffer, eeprom->bin.size);
+			spin_unlock(&eeprom->buffer_lock);
+		}
 		if (eeprom->idx_write_cnt < eeprom->num_address_bytes) {
 			if (eeprom->idx_write_cnt == 0)
 				eeprom->buffer_idx = 0;
@@ -69,7 +76,10 @@ static int i2c_slave_eeprom_slave_cb(struct i2c_client *client,
 		fallthrough;
 	case I2C_SLAVE_READ_REQUESTED:
 		spin_lock(&eeprom->buffer_lock);
-		*val = eeprom->buffer[eeprom->buffer_idx & eeprom->address_mask];
+		if (eeprom->latch)
+			*val = eeprom->buffer_latch[eeprom->buffer_idx & eeprom->address_mask];
+		else
+			*val = eeprom->buffer[eeprom->buffer_idx & eeprom->address_mask];
 		spin_unlock(&eeprom->buffer_lock);
 		/*
 		 * Do not increment buffer_idx here, because we don't know if
@@ -152,6 +162,17 @@ static int i2c_slave_eeprom_probe(struct i2c_client *client)
 	if (!eeprom)
 		return -ENOMEM;
 
+	if (of_property_read_bool(client->adapter->dev.of_node, "use-latch")) {
+		dev_info(&client->dev, "Using latch mode");
+		eeprom->latch = true;
+		eeprom->buffer_latch = devm_kzalloc(&client->dev, size, GFP_KERNEL);
+		if (!eeprom->buffer_latch)
+			return -ENOMEM;
+	} else {
+		eeprom->buffer_latch = NULL;
+		eeprom->latch = false;
+	}
+
 	eeprom->num_address_bytes = flag_addr16 ? 2 : 1;
 	eeprom->address_mask = size - 1;
 	eeprom->read_only = FIELD_GET(I2C_SLAVE_FLAG_RO, id->driver_data);
-- 
2.47.0