[PATCH 07/10] i2c: xiic: Switch to Xiic standard mode for i2c-read

Raviteja Narayanam raviteja.narayanam at xilinx.com
Mon May 31 06:19:45 PDT 2021


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 at xilinx.com>
---
 drivers/i2c/busses/i2c-xiic.c | 58 +++++++++++++++++++++++++++--------
 1 file changed, 45 insertions(+), 13 deletions(-)

diff --git a/drivers/i2c/busses/i2c-xiic.c b/drivers/i2c/busses/i2c-xiic.c
index 1a26e5ebfc6c..2f0808249ceb 100644
--- a/drivers/i2c/busses/i2c-xiic.c
+++ b/drivers/i2c/busses/i2c-xiic.c
@@ -33,6 +33,8 @@
 
 #define DRIVER_NAME "xiic-i2c"
 
+#define DYNAMIC_MODE_READ_BROKEN_BIT	BIT(0)
+
 enum xilinx_i2c_state {
 	STATE_DONE,
 	STATE_ERROR,
@@ -63,6 +65,7 @@ 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 +85,11 @@ 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
@@ -1032,6 +1040,7 @@ static int xiic_start_xfer(struct xiic_i2c *i2c)
 
 static int xiic_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
 {
+	bool broken_read, max_read_len, smbus_blk_read;
 	struct xiic_i2c *i2c = i2c_get_adapdata(adap);
 	int err, count;
 
@@ -1056,13 +1065,22 @@ static int xiic_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
 	i2c->prev_msg_tx = false;
 
 	/*
-	 * Enter standard mode only when read length is > 255 bytes or
-	 * for smbus_block_read transaction
+	 * 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++) {
-		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)) {
+		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;
 		}
@@ -1108,10 +1126,23 @@ 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;
@@ -1121,6 +1152,13 @@ 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))
@@ -1201,6 +1239,8 @@ static int xiic_i2c_probe(struct platform_device *pdev)
 			i2c_new_client_device(&i2c->adap, pdata->devices + i);
 	}
 
+	dev_info(&pdev->dev, "mmio %08lx irq %d\n", (unsigned long)res->start, irq);
+
 	return 0;
 
 err_clk_dis:
@@ -1232,14 +1272,6 @@ 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);
-- 
2.17.1




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