drm/bridge: it6505: add I2C functionality on AUX

DisplayPort AUX protocol supports I2C transport which is capable of
reading EDID or supports MCCS.

In drm_dp_helper, drm_dp_i2c_xfer() packs I2C requests into a
sequence of AUX requests.
it6505_aux_i2c_operation() is implemented to match drm_dp_i2c_xfer()
operactions.
it6505_aux_i2c_transfer() adds I2C functionality
for it6505_aux_transfer().

Reviewed-by: Dmitry Baryshkov <[email protected]>
Signed-off-by: Hermes Wu <[email protected]>
Reviewed-by: AngeloGioacchino Del Regno <[email protected]>
Signed-off-by: Dmitry Baryshkov <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/20241230-v7-upstream-v7-10-e0fdd4844703@ite.corp-partner.google.com

Author: Hermes Wu

drivers/gpu/drm/bridge/ite-it6505.c

@@ -268,6 +268,18 @@
 #define REG_SSC_CTRL1 0x189
 #define REG_SSC_CTRL2 0x18A
 
+#define REG_AUX_USER_CTRL 0x190
+#define EN_USER_AUX BIT(0)
+#define USER_AUX_DONE BIT(1)
+#define AUX_EVENT BIT(4)
+
+#define REG_AUX_USER_DATA_REC 0x191
+#define M_AUX_IN_REC   0xF0
+#define M_AUX_OUT_REC  0x0F
+
+#define REG_AUX_USER_REPLY 0x19A
+#define REG_AUX_USER_RXB(n) (n + 0x19B)
+
 #define RBR DP_LINK_BW_1_62
 #define HBR DP_LINK_BW_2_7
 #define HBR2 DP_LINK_BW_5_4
@@ -303,6 +315,8 @@
 #define MAX_EQ_LEVEL 0x03
 #define AUX_WAIT_TIMEOUT_MS 15
 #define AUX_FIFO_MAX_SIZE 16
+#define AUX_I2C_MAX_SIZE 4
+#define AUX_I2C_DEFER_RETRY 4
 #define PIXEL_CLK_DELAY 1
 #define PIXEL_CLK_INVERSE 0
 #define ADJUST_PHASE_THRESHOLD 80000
@@ -325,7 +339,12 @@
 enum aux_cmd_type {
 	CMD_AUX_NATIVE_READ = 0x0,
 	CMD_AUX_NATIVE_WRITE = 0x5,
+	CMD_AUX_GI2C_ADR = 0x08,
+	CMD_AUX_GI2C_READ = 0x09,
+	CMD_AUX_GI2C_WRITE = 0x0A,
 	CMD_AUX_I2C_EDID_READ = 0xB,
+	CMD_AUX_I2C_READ = 0x0D,
+	CMD_AUX_I2C_WRITE = 0x0C,
 
 	/* KSV read with AUX FIFO extend from CMD_AUX_NATIVE_READ*/
 	CMD_AUX_GET_KSV_LIST = 0x10,
@@ -1107,6 +1126,161 @@ static ssize_t it6505_aux_do_transfer(struct it6505 *it6505,
 	return ret;
 }
 
+static bool it6505_aux_i2c_reply_defer(u8 reply)
+{
+	if (reply == DP_AUX_NATIVE_REPLY_DEFER || reply == DP_AUX_I2C_REPLY_DEFER)
+		return true;
+	return false;
+}
+
+static bool it6505_aux_i2c_reply_nack(u8 reply)
+{
+	if (reply == DP_AUX_NATIVE_REPLY_NACK || reply == DP_AUX_I2C_REPLY_NACK)
+		return true;
+	return false;
+}
+
+static int it6505_aux_i2c_wait(struct it6505 *it6505, u8 *reply)
+{
+	int err = 0;
+	unsigned long timeout;
+	struct device *dev = it6505->dev;
+
+	timeout = jiffies + msecs_to_jiffies(AUX_WAIT_TIMEOUT_MS) + 1;
+
+	do {
+		if (it6505_read(it6505, REG_AUX_USER_CTRL) & AUX_EVENT)
+			break;
+		if (time_after(jiffies, timeout)) {
+			dev_err(dev, "Timed out waiting AUX I2C, BUSY = %X\n",
+				it6505_aux_op_finished(it6505));
+			err = -ETIMEDOUT;
+			goto end_aux_i2c_wait;
+		}
+		usleep_range(300, 800);
+	} while (!it6505_aux_op_finished(it6505));
+
+	*reply = it6505_read(it6505, REG_AUX_USER_REPLY) >> 4;
+
+	if (*reply == 0)
+		goto end_aux_i2c_wait;
+
+	if (it6505_aux_i2c_reply_defer(*reply))
+		err = -EBUSY;
+	else if (it6505_aux_i2c_reply_nack(*reply))
+		err = -ENXIO;
+
+end_aux_i2c_wait:
+	it6505_set_bits(it6505, REG_AUX_USER_CTRL, USER_AUX_DONE, USER_AUX_DONE);
+	return err;
+}
+
+static int it6505_aux_i2c_readb(struct it6505 *it6505, u8 *buf, size_t size, u8 *reply)
+{
+	int ret, i;
+	int retry;
+
+	for (retry = 0; retry < AUX_I2C_DEFER_RETRY; retry++) {
+		it6505_write(it6505, REG_AUX_CMD_REQ, CMD_AUX_GI2C_READ);
+
+		ret = it6505_aux_i2c_wait(it6505, reply);
+		if (it6505_aux_i2c_reply_defer(*reply))
+			continue;
+		if (ret >= 0)
+			break;
+	}
+
+	for (i = 0; i < size; i++)
+		buf[i] = it6505_read(it6505, REG_AUX_USER_RXB(0 + i));
+
+	return size;
+}
+
+static int it6505_aux_i2c_writeb(struct it6505 *it6505, u8 *buf, size_t size, u8 *reply)
+{
+	int i, ret;
+	int retry;
+
+	for (i = 0; i < size; i++)
+		it6505_write(it6505, REG_AUX_OUT_DATA0 + i, buf[i]);
+
+	for (retry = 0; retry < AUX_I2C_DEFER_RETRY; retry++) {
+		it6505_write(it6505, REG_AUX_CMD_REQ, CMD_AUX_GI2C_WRITE);
+
+		ret = it6505_aux_i2c_wait(it6505, reply);
+		if (it6505_aux_i2c_reply_defer(*reply))
+			continue;
+		if (ret >= 0)
+			break;
+	}
+	return size;
+}
+
+static ssize_t it6505_aux_i2c_operation(struct it6505 *it6505,
+					struct drm_dp_aux_msg *msg)
+{
+	int ret;
+	ssize_t request_size, data_cnt = 0;
+	u8 *buffer = msg->buffer;
+
+	/* set AUX user mode */
+	it6505_set_bits(it6505, REG_AUX_CTRL,
+			AUX_USER_MODE | AUX_NO_SEGMENT_WR, AUX_USER_MODE);
+	it6505_set_bits(it6505, REG_AUX_USER_CTRL, EN_USER_AUX, EN_USER_AUX);
+	/* clear AUX FIFO */
+	it6505_set_bits(it6505, REG_AUX_CTRL,
+			AUX_EN_FIFO_READ | CLR_EDID_FIFO,
+			AUX_EN_FIFO_READ | CLR_EDID_FIFO);
+
+	it6505_set_bits(it6505, REG_AUX_CTRL,
+			AUX_EN_FIFO_READ | CLR_EDID_FIFO, 0x00);
+
+	it6505_write(it6505, REG_AUX_ADR_0_7, 0x00);
+	it6505_write(it6505, REG_AUX_ADR_8_15, msg->address << 1);
+
+	if (msg->size == 0) {
+		/* IIC Start/STOP dummy write */
+		it6505_write(it6505, REG_AUX_ADR_16_19, msg->request);
+		it6505_write(it6505, REG_AUX_CMD_REQ, CMD_AUX_GI2C_ADR);
+		ret = it6505_aux_i2c_wait(it6505, &msg->reply);
+		goto end_aux_i2c_transfer;
+	}
+
+	/* IIC data transfer */
+	data_cnt = 0;
+	do {
+		request_size = min_t(ssize_t, msg->size - data_cnt, AUX_I2C_MAX_SIZE);
+		it6505_write(it6505, REG_AUX_ADR_16_19,
+			     msg->request | ((request_size - 1) << 4));
+		if ((msg->request & DP_AUX_I2C_READ) == DP_AUX_I2C_READ)
+			ret = it6505_aux_i2c_readb(it6505, &buffer[data_cnt],
+						   request_size, &msg->reply);
+		else
+			ret = it6505_aux_i2c_writeb(it6505, &buffer[data_cnt],
+						    request_size, &msg->reply);
+
+		if (ret < 0)
+			goto end_aux_i2c_transfer;
+
+		data_cnt += request_size;
+	} while (data_cnt < msg->size);
+	ret = data_cnt;
+end_aux_i2c_transfer:
+
+	it6505_set_bits(it6505, REG_AUX_USER_CTRL, EN_USER_AUX, 0);
+	it6505_set_bits(it6505, REG_AUX_CTRL, AUX_USER_MODE, 0);
+	return ret;
+}
+
+static ssize_t it6505_aux_i2c_transfer(struct drm_dp_aux *aux,
+				       struct drm_dp_aux_msg *msg)
+{
+	struct it6505 *it6505 = container_of(aux, struct it6505, aux);
+
+	guard(mutex)(&it6505->aux_lock);
+	return it6505_aux_i2c_operation(it6505, msg);
+}
+
 static ssize_t it6505_aux_transfer(struct drm_dp_aux *aux,
 				   struct drm_dp_aux_msg *msg)
 {
@@ -1116,9 +1290,8 @@ static ssize_t it6505_aux_transfer(struct drm_dp_aux *aux,
 	int ret;
 	enum aux_cmd_reply reply;
 
-	/* IT6505 doesn't support arbitrary I2C read / write. */
 	if (is_i2c)
-		return -EINVAL;
+		return it6505_aux_i2c_transfer(aux, msg);
 
 	switch (msg->request) {
 	case DP_AUX_NATIVE_READ: