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From:   Raviteja Narayanam <raviteja.narayanam@xilinx.com>
To:     <linux-i2c@vger.kernel.org>, <michal.simek@xilinx.com>
CC:     <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>, <git@xilinx.com>, <marex@denx.de>,
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        Raviteja Narayanam <raviteja.narayanam@xilinx.com>
Subject: [PATCH v2 03/10] i2c: xiic: Switch to Xiic standard mode for i2c-read
Date:   Sat, 26 Jun 2021 15:57:59 +0530
Message-ID: <20210626102806.15402-4-raviteja.narayanam@xilinx.com>
In-Reply-To: <20210626102806.15402-1-raviteja.narayanam@xilinx.com>
References: <20210626102806.15402-1-raviteja.narayanam@xilinx.com>
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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@xilinx.com>
---
 drivers/i2c/busses/i2c-xiic.c | 54 ++++++++++++++++++++++++++++-------
 1 file changed, 43 insertions(+), 11 deletions(-)

diff --git a/drivers/i2c/busses/i2c-xiic.c b/drivers/i2c/busses/i2c-xiic.c
index 004103267e9c..c31d0d0a8384 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,
@@ -62,6 +64,7 @@ enum xiic_endian {
  * @singlemaster: Indicates bus is single master
  * @dynamic: Mode of controller
  * @prev_msg_tx: Previous message is Tx
+ * @quirks: To hold platform specific bug info
  */
 struct xiic_i2c {
 	struct device *dev;
@@ -80,8 +83,12 @@ struct xiic_i2c {
 	bool singlemaster;
 	bool dynamic;
 	bool prev_msg_tx;
+	u32 quirks;
 };
 
+struct xiic_version_data {
+	u32 quirks;
+};
 
 #define XIIC_MSB_OFFSET 0
 #define XIIC_REG_OFFSET (0x100+XIIC_MSB_OFFSET)
@@ -963,6 +970,7 @@ 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;
 	struct xiic_i2c *i2c = i2c_get_adapdata(adap);
 	int err, count;
 
@@ -986,10 +994,21 @@ static int xiic_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
 	/* Initialize prev message type */
 	i2c->prev_msg_tx = false;
 
-	/* Enter standard mode only when read length is > 255 bytes */
+	/*
+	 * Scan through nmsgs, use dynamic mode when none of the below two
+	 * 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.
+	 */
 	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) {
+		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);
+
+		if (broken_read || max_read_len) {
 			i2c->dynamic = false;
 			break;
 		}
@@ -1035,11 +1054,23 @@ 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;
@@ -1049,6 +1080,13 @@ 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))
@@ -1129,6 +1167,8 @@ 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:
@@ -1160,14 +1200,6 @@ 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