[PATCH 07/12] i2c: xiic: Switch to Xiic standard mode for i2c-read

[Manikanta Guntupalli]

From: Raviteja Narayanam <raviteja.narayanam@xxxxxxxxxx>

Xilinx I2C IP has two modes of operation, both of which implement
I2C transactions. The only difference from sw perspective is the
programming sequence for these modes.
Dynamic mode  -> Simple to program, less number of steps in sequence.
Standard mode -> Gives flexibility, more number of steps in sequence.

In dynamic mode, during the i2c-read transactions, if there is a
delay(> 200us) between the register writes (address & byte count),
read transaction fails. On a system with load, this scenario is
occurring frequently.
To avoid this, switch to standard mode if there is a read request.

Added a quirk to identify the IP version effected by this and follow
the standard mode.

Signed-off-by: Raviteja Narayanam <raviteja.narayanam@xxxxxxxxxx>
Signed-off-by: Manikanta Guntupalli <manikanta.guntupalli@xxxxxxxxxx>
---
 drivers/i2c/busses/i2c-xiic.c | 87 +++++++++++++++++++++++------------
 1 file changed, 58 insertions(+), 29 deletions(-)

diff --git a/drivers/i2c/busses/i2c-xiic.c b/drivers/i2c/busses/i2c-xiic.c
index 57ede62de67d..74cd50478694 100644
--- a/drivers/i2c/busses/i2c-xiic.c
+++ b/drivers/i2c/busses/i2c-xiic.c
@@ -32,6 +32,7 @@
 #include <linux/pm_runtime.h>
 
 #define DRIVER_NAME "xiic-i2c"
+#define DYNAMIC_MODE_READ_BROKEN_BIT	BIT(0)
 
 enum xilinx_i2c_state {
 	STATE_DONE,
@@ -63,6 +64,7 @@ enum xiic_endian {
  * @dynamic: Mode of controller
  * @prev_msg_tx: Previous message is Tx
  * @smbus_block_read: Flag to handle block read
+ * @quirks: To hold platform specific bug info
  */
 struct xiic_i2c {
 	struct device *dev;
@@ -82,6 +84,11 @@ struct xiic_i2c {
 	bool dynamic;
 	bool prev_msg_tx;
 	bool smbus_block_read;
+	u32 quirks;
+};
+
+struct xiic_version_data {
+	u32 quirks;
 };
 
 #define XIIC_MSB_OFFSET 0
@@ -995,7 +1002,8 @@ static void __xiic_start_xfer(struct xiic_i2c *i2c)
 
 static int xiic_start_xfer(struct xiic_i2c *i2c, struct i2c_msg *msgs, int num)
 {
-	int ret;
+	bool broken_read, max_read_len, smbus_blk_read;
+	int ret, count;
 
 	mutex_lock(&i2c->lock);
 
@@ -1008,6 +1016,34 @@ static int xiic_start_xfer(struct xiic_i2c *i2c, struct i2c_msg *msgs, int num)
 	i2c->nmsgs = num;
 	init_completion(&i2c->completion);
 
+	/* Decide standard mode or Dynamic mode */
+	i2c->dynamic = true;
+
+	/* Initialize prev message type */
+	i2c->prev_msg_tx = false;
+
+	/*
+	 * Scan through nmsgs, use dynamic mode when none of the below three
+	 * conditions occur. We need standard mode even if one condition holds
+	 * true in the entire array of messages in a single transfer.
+	 * If read transaction as dynamic mode is broken for delayed reads
+	 * in xlnx,axi-iic-2.0 / xlnx,xps-iic-2.00.a IP versions.
+	 * If read length is > 255 bytes.
+	 * If smbus_block_read transaction.
+	 */
+	for (count = 0; count < i2c->nmsgs; count++) {
+		broken_read = (i2c->quirks & DYNAMIC_MODE_READ_BROKEN_BIT) &&
+				(i2c->tx_msg[count].flags & I2C_M_RD);
+		max_read_len = (i2c->tx_msg[count].flags & I2C_M_RD) &&
+				(i2c->tx_msg[count].len > MAX_READ_LENGTH_DYNAMIC);
+		smbus_blk_read = (i2c->tx_msg[count].flags & I2C_M_RECV_LEN);
+
+		if (broken_read || max_read_len || smbus_blk_read) {
+			i2c->dynamic = false;
+			break;
+		}
+	}
+
 	ret = xiic_reinit(i2c);
 	if (!ret)
 		__xiic_start_xfer(i2c);
@@ -1021,7 +1057,7 @@ static int xiic_start_xfer(struct xiic_i2c *i2c, struct i2c_msg *msgs, int num)
 static int xiic_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
 {
 	struct xiic_i2c *i2c = i2c_get_adapdata(adap);
-	int err, count;
+	int err;
 
 	dev_dbg(adap->dev.parent, "%s entry SR: 0x%x\n", __func__,
 		xiic_getreg8(i2c, XIIC_SR_REG_OFFSET));
@@ -1030,25 +1066,6 @@ static int xiic_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
 	if (err < 0)
 		return err;
 
-	/* Decide standard mode or Dynamic mode */
-	i2c->dynamic = true;
-
-	/* Initialize prev message type */
-	i2c->prev_msg_tx = false;
-
-	/*
-	 * Enter standard mode only when read length is > 255 bytes or
-	 * for smbus_block_read transaction
-	 */
-	for (count = 0; count < i2c->nmsgs; count++) {
-		if (((i2c->tx_msg[count].flags & I2C_M_RD) &&
-		     i2c->tx_msg[count].len > MAX_READ_LENGTH_DYNAMIC) ||
-		    (i2c->tx_msg[count].flags & I2C_M_RECV_LEN)) {
-			i2c->dynamic = false;
-			break;
-		}
-	}
-
 	err = xiic_start_xfer(i2c, msgs, num);
 	if (err < 0) {
 		dev_err(adap->dev.parent, "Error xiic_start_xfer\n");
@@ -1091,10 +1108,23 @@ static const struct i2c_adapter xiic_adapter = {
 	.algo = &xiic_algorithm,
 };
 
+static const struct xiic_version_data xiic_2_00 = {
+	.quirks = DYNAMIC_MODE_READ_BROKEN_BIT,
+};
+
+#if defined(CONFIG_OF)
+static const struct of_device_id xiic_of_match[] = {
+	{ .compatible = "xlnx,xps-iic-2.00.a", .data = &xiic_2_00 },
+	{},
+};
+MODULE_DEVICE_TABLE(of, xiic_of_match);
+#endif
+
 static int xiic_i2c_probe(struct platform_device *pdev)
 {
 	struct xiic_i2c *i2c;
 	struct xiic_i2c_platform_data *pdata;
+	const struct of_device_id *match;
 	struct resource *res;
 	int ret, irq;
 	u8 i;
@@ -1104,6 +1134,13 @@ static int xiic_i2c_probe(struct platform_device *pdev)
 	if (!i2c)
 		return -ENOMEM;
 
+	match = of_match_node(xiic_of_match, pdev->dev.of_node);
+	if (match && match->data) {
+		const struct xiic_version_data *data = match->data;
+
+		i2c->quirks = data->quirks;
+	}
+
 	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 	i2c->base = devm_ioremap_resource(&pdev->dev, res);
 	if (IS_ERR(i2c->base))
@@ -1215,14 +1252,6 @@ static int xiic_i2c_remove(struct platform_device *pdev)
 	return 0;
 }
 
-#if defined(CONFIG_OF)
-static const struct of_device_id xiic_of_match[] = {
-	{ .compatible = "xlnx,xps-iic-2.00.a", },
-	{},
-};
-MODULE_DEVICE_TABLE(of, xiic_of_match);
-#endif
-
 static int __maybe_unused xiic_i2c_runtime_suspend(struct device *dev)
 {
 	struct xiic_i2c *i2c = dev_get_drvdata(dev);
-- 
2.25.1