From 371cb1f31574fd9d6a706986c3971588a761a9c9 Mon Sep 17 00:00:00 2001
From: Phil Elwell <phil@raspberrypi.com>
Date: Fri, 4 Dec 2020 15:20:36 +0000
Subject: [PATCH 0535/1085] i2c: designware: Add SMBUS quick command support

The SMBUS emulation code turns an SMBUS quick command into a zero-
length read. This controller can't do zero length accesses, but it
can do quick commands, so reverse the emulation. The alternative
would be to properly implement the SMBUS support but that is a lot
more work, and unnecessary just to get i2cdetect working.

Signed-off-by: Phil Elwell <phil@raspberrypi.com>
---
 drivers/i2c/busses/i2c-designware-core.h   |  2 ++
 drivers/i2c/busses/i2c-designware-master.c | 17 +++++++++++++++--
 2 files changed, 17 insertions(+), 2 deletions(-)

--- a/drivers/i2c/busses/i2c-designware-core.h
+++ b/drivers/i2c/busses/i2c-designware-core.h
@@ -124,7 +124,9 @@
 
 #define DW_IC_ERR_TX_ABRT			0x1
 
+#define DW_IC_TAR_SPECIAL			BIT(11)
 #define DW_IC_TAR_10BITADDR_MASTER		BIT(12)
+#define DW_IC_TAR_SMBUS_QUICK_CMD		BIT(16)
 
 #define DW_IC_COMP_PARAM_1_SPEED_MODE_HIGH	(BIT(2) | BIT(3))
 #define DW_IC_COMP_PARAM_1_SPEED_MODE_MASK	GENMASK(3, 2)
--- a/drivers/i2c/busses/i2c-designware-master.c
+++ b/drivers/i2c/busses/i2c-designware-master.c
@@ -229,6 +229,10 @@ static void i2c_dw_xfer_init(struct dw_i
 		ic_tar = DW_IC_TAR_10BITADDR_MASTER;
 	}
 
+	/* Convert a zero-length read into an SMBUS quick command */
+	if (!msgs[dev->msg_write_idx].len)
+		ic_tar = DW_IC_TAR_SPECIAL | DW_IC_TAR_SMBUS_QUICK_CMD;
+
 	regmap_update_bits(dev->map, DW_IC_CON, DW_IC_CON_10BITADDR_MASTER,
 			   ic_con);
 
@@ -500,6 +504,14 @@ i2c_dw_xfer_msg(struct dw_i2c_dev *dev)
 		regmap_read(dev->map, DW_IC_RXFLR, &flr);
 		rx_limit = dev->rx_fifo_depth - flr;
 
+		/* Handle SMBUS quick commands */
+		if (!buf_len) {
+			if (msgs[dev->msg_write_idx].flags & I2C_M_RD)
+				regmap_write(dev->map, DW_IC_DATA_CMD, 0x300);
+			else
+				regmap_write(dev->map, DW_IC_DATA_CMD, 0x200);
+		}
+
 		while (buf_len > 0 && tx_limit > 0 && rx_limit > 0) {
 			u32 cmd = 0;
 
@@ -781,7 +793,7 @@ static const struct i2c_algorithm i2c_dw
 };
 
 static const struct i2c_adapter_quirks i2c_dw_quirks = {
-	.flags = I2C_AQ_NO_ZERO_LEN,
+	.flags = 0,
 };
 
 static u32 i2c_dw_read_clear_intrbits(struct dw_i2c_dev *dev)
@@ -914,7 +926,8 @@ void i2c_dw_configure_master(struct dw_i
 {
 	struct i2c_timings *t = &dev->timings;
 
-	dev->functionality = I2C_FUNC_10BIT_ADDR | DW_IC_DEFAULT_FUNCTIONALITY;
+	dev->functionality = I2C_FUNC_10BIT_ADDR | I2C_FUNC_SMBUS_QUICK |
+			     DW_IC_DEFAULT_FUNCTIONALITY;
 
 	dev->master_cfg = DW_IC_CON_MASTER | DW_IC_CON_SLAVE_DISABLE |
 			  DW_IC_CON_RESTART_EN;
