Merge branch 'i2c/quirks' into i2c/for-4.1

Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

drivers/i2c/busses/i2c-at91.c

@@ -487,30 +487,10 @@ static int at91_twi_xfer(struct i2c_adapter *adap, struct i2c_msg *msg, int num)
 	if (ret < 0)
 		goto out;
 
-	/*
-	 * The hardware can handle at most two messages concatenated by a
-	 * repeated start via it's internal address feature.
-	 */
-	if (num > 2) {
-		dev_err(dev->dev,
-			"cannot handle more than two concatenated messages.\n");
-		ret = 0;
-		goto out;
-	} else if (num == 2) {
+	if (num == 2) {
 		int internal_address = 0;
 		int i;
 
-		if (msg->flags & I2C_M_RD) {
-			dev_err(dev->dev, "first transfer must be write.\n");
-			ret = -EINVAL;
-			goto out;
-		}
-		if (msg->len > 3) {
-			dev_err(dev->dev, "first message size must be <= 3.\n");
-			ret = -EINVAL;
-			goto out;
-		}
-
 		/* 1st msg is put into the internal address, start with 2nd */
 		m_start = &msg[1];
 		for (i = 0; i < msg->len; ++i) {
@@ -540,6 +520,15 @@ static int at91_twi_xfer(struct i2c_adapter *adap, struct i2c_msg *msg, int num)
 	return ret;
 }
 
+/*
+ * The hardware can handle at most two messages concatenated by a
+ * repeated start via it's internal address feature.
+ */
+static struct i2c_adapter_quirks at91_twi_quirks = {
+	.flags = I2C_AQ_COMB | I2C_AQ_COMB_WRITE_FIRST | I2C_AQ_COMB_SAME_ADDR,
+	.max_comb_1st_msg_len = 3,
+};
+
 static u32 at91_twi_func(struct i2c_adapter *adapter)
 {
 	return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL
@@ -777,6 +766,7 @@ static int at91_twi_probe(struct platform_device *pdev)
 	dev->adapter.owner = THIS_MODULE;
 	dev->adapter.class = I2C_CLASS_DEPRECATED;
 	dev->adapter.algo = &at91_twi_algorithm;
+	dev->adapter.quirks = &at91_twi_quirks;
 	dev->adapter.dev.parent = dev->dev;
 	dev->adapter.nr = pdev->id;
 	dev->adapter.timeout = AT91_I2C_TIMEOUT;

drivers/i2c/busses/i2c-axxia.c

@@ -336,11 +336,6 @@ static int axxia_i2c_xfer_msg(struct axxia_i2c_dev *idev, struct i2c_msg *msg)
 	u32 addr_1, addr_2;
 	int ret;
 
-	if (msg->len > 255) {
-		dev_warn(idev->dev, "unsupported length %u\n", msg->len);
-		return -EINVAL;
-	}
-
 	idev->msg = msg;
 	idev->msg_xfrd = 0;
 	idev->msg_err = 0;
@@ -454,6 +449,11 @@ static const struct i2c_algorithm axxia_i2c_algo = {
 	.functionality = axxia_i2c_func,
 };
 
+static struct i2c_adapter_quirks axxia_i2c_quirks = {
+	.max_read_len = 255,
+	.max_write_len = 255,
+};
+
 static int axxia_i2c_probe(struct platform_device *pdev)
 {
 	struct device_node *np = pdev->dev.of_node;
@@ -511,6 +511,7 @@ static int axxia_i2c_probe(struct platform_device *pdev)
 	strlcpy(idev->adapter.name, pdev->name, sizeof(idev->adapter.name));
 	idev->adapter.owner = THIS_MODULE;
 	idev->adapter.algo = &axxia_i2c_algo;
+	idev->adapter.quirks = &axxia_i2c_quirks;
 	idev->adapter.dev.parent = &pdev->dev;
 	idev->adapter.dev.of_node = pdev->dev.of_node;
 

drivers/i2c/busses/i2c-bcm-iproc.c

@@ -160,14 +160,6 @@ static int bcm_iproc_i2c_xfer_single_msg(struct bcm_iproc_i2c_dev *iproc_i2c,
 	u32 val;
 	unsigned long time_left = msecs_to_jiffies(I2C_TIMEOUT_MESC);
 
-	/* need to reserve one byte in the FIFO for the slave address */
-	if (msg->len > M_TX_RX_FIFO_SIZE - 1) {
-		dev_err(iproc_i2c->device,
-			"only support data length up to %u bytes\n",
-			M_TX_RX_FIFO_SIZE - 1);
-		return -EOPNOTSUPP;
-	}
-
 	/* check if bus is busy */
 	if (!!(readl(iproc_i2c->base + M_CMD_OFFSET) &
 	       BIT(M_CMD_START_BUSY_SHIFT))) {
@@ -287,6 +279,12 @@ static const struct i2c_algorithm bcm_iproc_algo = {
 	.functionality = bcm_iproc_i2c_functionality,
 };
 
+static struct i2c_adapter_quirks bcm_iproc_i2c_quirks = {
+	/* need to reserve one byte in the FIFO for the slave address */
+	.max_read_len = M_TX_RX_FIFO_SIZE - 1,
+	.max_write_len = M_TX_RX_FIFO_SIZE - 1,
+};
+
 static int bcm_iproc_i2c_cfg_speed(struct bcm_iproc_i2c_dev *iproc_i2c)
 {
 	unsigned int bus_speed;
@@ -413,6 +411,7 @@ static int bcm_iproc_i2c_probe(struct platform_device *pdev)
 	i2c_set_adapdata(adap, iproc_i2c);
 	strlcpy(adap->name, "Broadcom iProc I2C adapter", sizeof(adap->name));
 	adap->algo = &bcm_iproc_algo;
+	adap->quirks = &bcm_iproc_i2c_quirks;
 	adap->dev.parent = &pdev->dev;
 	adap->dev.of_node = pdev->dev.of_node;
 

drivers/i2c/busses/i2c-cpm.c

@@ -308,22 +308,12 @@ static int cpm_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
 	struct i2c_reg __iomem *i2c_reg = cpm->i2c_reg;
 	struct i2c_ram __iomem *i2c_ram = cpm->i2c_ram;
 	struct i2c_msg *pmsg;
-	int ret, i;
+	int ret;
 	int tptr;
 	int rptr;
 	cbd_t __iomem *tbdf;
 	cbd_t __iomem *rbdf;
 
-	if (num > CPM_MAXBD)
-		return -EINVAL;
-
-	/* Check if we have any oversized READ requests */
-	for (i = 0; i < num; i++) {
-		pmsg = &msgs[i];
-		if (pmsg->len >= CPM_MAX_READ)
-			return -EINVAL;
-	}
-
 	/* Reset to use first buffer */
 	out_be16(&i2c_ram->rbptr, in_be16(&i2c_ram->rbase));
 	out_be16(&i2c_ram->tbptr, in_be16(&i2c_ram->tbase));
@@ -424,10 +414,18 @@ static const struct i2c_algorithm cpm_i2c_algo = {
 	.functionality = cpm_i2c_func,
 };
 
+/* CPM_MAX_READ is also limiting writes according to the code! */
+static struct i2c_adapter_quirks cpm_i2c_quirks = {
+	.max_num_msgs = CPM_MAXBD,
+	.max_read_len = CPM_MAX_READ,
+	.max_write_len = CPM_MAX_READ,
+};
+
 static const struct i2c_adapter cpm_ops = {
 	.owner		= THIS_MODULE,
 	.name		= "i2c-cpm",
 	.algo		= &cpm_i2c_algo,
+	.quirks		= &cpm_i2c_quirks,
 };
 
 static int cpm_i2c_setup(struct cpm_i2c *cpm)

drivers/i2c/busses/i2c-dln2.c

@@ -144,7 +144,6 @@ static int dln2_i2c_xfer(struct i2c_adapter *adapter,
 {
 	struct dln2_i2c *dln2 = i2c_get_adapdata(adapter);
 	struct i2c_msg *pmsg;
-	struct device *dev = &dln2->adapter.dev;
 	int i;
 
 	for (i = 0; i < num; i++) {
@@ -152,11 +151,6 @@ static int dln2_i2c_xfer(struct i2c_adapter *adapter,
 
 		pmsg = &msgs[i];
 
-		if (pmsg->len > DLN2_I2C_MAX_XFER_SIZE) {
-			dev_warn(dev, "maximum transfer size exceeded\n");
-			return -EOPNOTSUPP;
-		}
-
 		if (pmsg->flags & I2C_M_RD) {
 			ret = dln2_i2c_read(dln2, pmsg->addr, pmsg->buf,
 					    pmsg->len);
@@ -187,6 +181,11 @@ static const struct i2c_algorithm dln2_i2c_usb_algorithm = {
 	.functionality = dln2_i2c_func,
 };
 
+static struct i2c_adapter_quirks dln2_i2c_quirks = {
+	.max_read_len = DLN2_I2C_MAX_XFER_SIZE,
+	.max_write_len = DLN2_I2C_MAX_XFER_SIZE,
+};
+
 static int dln2_i2c_probe(struct platform_device *pdev)
 {
 	int ret;
@@ -209,6 +208,7 @@ static int dln2_i2c_probe(struct platform_device *pdev)
 	dln2->adapter.owner = THIS_MODULE;
 	dln2->adapter.class = I2C_CLASS_HWMON;
 	dln2->adapter.algo = &dln2_i2c_usb_algorithm;
+	dln2->adapter.quirks = &dln2_i2c_quirks;
 	dln2->adapter.dev.parent = dev;
 	i2c_set_adapdata(&dln2->adapter, dln2);
 	snprintf(dln2->adapter.name, sizeof(dln2->adapter.name), "%s-%s-%d",

drivers/i2c/busses/i2c-opal.c

@@ -104,18 +104,8 @@ static int i2c_opal_master_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
 		req.buffer_ra = cpu_to_be64(__pa(msgs[0].buf));
 		break;
 	case 2:
-		/* For two messages, we basically support only simple
-		 * smbus transactions of a write plus a read. We might
-		 * want to allow also two writes but we'd have to bounce
-		 * the data into a single buffer.
-		 */
-		if ((msgs[0].flags & I2C_M_RD) || !(msgs[1].flags & I2C_M_RD))
-			return -EOPNOTSUPP;
-		if (msgs[0].len > 4)
-			return -EOPNOTSUPP;
-		if (msgs[0].addr != msgs[1].addr)
-			return -EOPNOTSUPP;
-		req.type = OPAL_I2C_SM_READ;
+		req.type = (msgs[1].flags & I2C_M_RD) ?
+			OPAL_I2C_SM_READ : OPAL_I2C_SM_WRITE;
 		req.addr = cpu_to_be16(msgs[0].addr);
 		req.subaddr_sz = msgs[0].len;
 		for (i = 0; i < msgs[0].len; i++)
@@ -210,6 +200,15 @@ static const struct i2c_algorithm i2c_opal_algo = {
 	.functionality	= i2c_opal_func,
 };
 
+/*
+ * For two messages, we basically support simple smbus transactions of a
+ * write-then-anything.
+ */
+static struct i2c_adapter_quirks i2c_opal_quirks = {
+	.flags = I2C_AQ_COMB | I2C_AQ_COMB_WRITE_FIRST | I2C_AQ_COMB_SAME_ADDR,
+	.max_comb_1st_msg_len = 4,
+};
+
 static int i2c_opal_probe(struct platform_device *pdev)
 {
 	struct i2c_adapter	*adapter;
@@ -232,6 +231,7 @@ static int i2c_opal_probe(struct platform_device *pdev)
 
 	adapter->algo = &i2c_opal_algo;
 	adapter->algo_data = (void *)(unsigned long)opal_id;
+	adapter->quirks = &i2c_opal_quirks;
 	adapter->dev.parent = &pdev->dev;
 	adapter->dev.of_node = of_node_get(pdev->dev.of_node);
 	pname = of_get_property(pdev->dev.of_node, "ibm,port-name", NULL);

drivers/i2c/busses/i2c-pmcmsp.c

@@ -456,14 +456,6 @@ static enum pmcmsptwi_xfer_result pmcmsptwi_xfer_cmd(
 		return -EINVAL;
 	}
 
-	if (cmd->read_len > MSP_MAX_BYTES_PER_RW ||
-	    cmd->write_len > MSP_MAX_BYTES_PER_RW) {
-		dev_err(&pmcmsptwi_adapter.dev,
-			"%s: Cannot transfer more than %d bytes\n",
-			__func__, MSP_MAX_BYTES_PER_RW);
-		return -EINVAL;
-	}
-
 	mutex_lock(&data->lock);
 	dev_dbg(&pmcmsptwi_adapter.dev,
 		"Setting address to 0x%04x\n", cmd->addr);
@@ -520,25 +512,14 @@ static int pmcmsptwi_master_xfer(struct i2c_adapter *adap,
 	struct pmcmsptwi_cfg oldcfg, newcfg;
 	int ret;
 
-	if (num > 2) {
-		dev_dbg(&adap->dev, "%d messages unsupported\n", num);
-		return -EINVAL;
-	} else if (num == 2) {
-		/* Check for a dual write-then-read command */
+	if (num == 2) {
 		struct i2c_msg *nextmsg = msg + 1;
-		if (!(msg->flags & I2C_M_RD) &&
-		    (nextmsg->flags & I2C_M_RD) &&
-		    msg->addr == nextmsg->addr) {
-			cmd.type = MSP_TWI_CMD_WRITE_READ;
-			cmd.write_len = msg->len;
-			cmd.write_data = msg->buf;
-			cmd.read_len = nextmsg->len;
-			cmd.read_data = nextmsg->buf;
-		} else {
-			dev_dbg(&adap->dev,
-				"Non write-read dual messages unsupported\n");
-			return -EINVAL;
-		}
+
+		cmd.type = MSP_TWI_CMD_WRITE_READ;
+		cmd.write_len = msg->len;
+		cmd.write_data = msg->buf;
+		cmd.read_len = nextmsg->len;
+		cmd.read_data = nextmsg->buf;
 	} else if (msg->flags & I2C_M_RD) {
 		cmd.type = MSP_TWI_CMD_READ;
 		cmd.read_len = msg->len;
@@ -598,6 +579,14 @@ static u32 pmcmsptwi_i2c_func(struct i2c_adapter *adapter)
 		I2C_FUNC_SMBUS_WORD_DATA | I2C_FUNC_SMBUS_PROC_CALL;
 }
 
+static struct i2c_adapter_quirks pmcmsptwi_i2c_quirks = {
+	.flags = I2C_AQ_COMB_WRITE_THEN_READ,
+	.max_write_len = MSP_MAX_BYTES_PER_RW,
+	.max_read_len = MSP_MAX_BYTES_PER_RW,
+	.max_comb_1st_msg_len = MSP_MAX_BYTES_PER_RW,
+	.max_comb_2nd_msg_len = MSP_MAX_BYTES_PER_RW,
+};
+
 /* -- Initialization -- */
 
 static struct i2c_algorithm pmcmsptwi_algo = {
@@ -609,6 +598,7 @@ static struct i2c_adapter pmcmsptwi_adapter = {
 	.owner		= THIS_MODULE,
 	.class		= I2C_CLASS_HWMON | I2C_CLASS_SPD,
 	.algo		= &pmcmsptwi_algo,
+	.quirks		= &pmcmsptwi_i2c_quirks,
 	.name		= DRV_NAME,
 };
 

drivers/i2c/busses/i2c-powermac.c

@@ -153,12 +153,6 @@ static int i2c_powermac_master_xfer(	struct i2c_adapter *adap,
 	int			read;
 	int			addrdir;
 
-	if (num != 1) {
-		dev_err(&adap->dev,
-			"Multi-message I2C transactions not supported\n");
-		return -EOPNOTSUPP;
-	}
-
 	if (msgs->flags & I2C_M_TEN)
 		return -EINVAL;
 	read = (msgs->flags & I2C_M_RD) != 0;
@@ -205,6 +199,9 @@ static const struct i2c_algorithm i2c_powermac_algorithm = {
 	.functionality	= i2c_powermac_func,
 };
 
+static struct i2c_adapter_quirks i2c_powermac_quirks = {
+	.max_num_msgs = 1,
+};
 
 static int i2c_powermac_remove(struct platform_device *dev)
 {
@@ -434,6 +431,7 @@ static int i2c_powermac_probe(struct platform_device *dev)
 
 	platform_set_drvdata(dev, adapter);
 	adapter->algo = &i2c_powermac_algorithm;
+	adapter->quirks = &i2c_powermac_quirks;
 	i2c_set_adapdata(adapter, bus);
 	adapter->dev.parent = &dev->dev;
 

drivers/i2c/busses/i2c-qup.c

@@ -412,17 +412,6 @@ static int qup_i2c_read_one(struct qup_i2c_dev *qup, struct i2c_msg *msg)
 	unsigned long left;
 	int ret;
 
-	/*
-	 * The QUP block will issue a NACK and STOP on the bus when reaching
-	 * the end of the read, the length of the read is specified as one byte
-	 * which limits the possible read to 256 (QUP_READ_LIMIT) bytes.
-	 */
-	if (msg->len > QUP_READ_LIMIT) {
-		dev_err(qup->dev, "HW not capable of reads over %d bytes\n",
-			QUP_READ_LIMIT);
-		return -EINVAL;
-	}
-
 	qup->msg = msg;
 	qup->pos  = 0;
 
@@ -534,6 +523,15 @@ static const struct i2c_algorithm qup_i2c_algo = {
 	.functionality	= qup_i2c_func,
 };
 
+/*
+ * The QUP block will issue a NACK and STOP on the bus when reaching
+ * the end of the read, the length of the read is specified as one byte
+ * which limits the possible read to 256 (QUP_READ_LIMIT) bytes.
+ */
+static struct i2c_adapter_quirks qup_i2c_quirks = {
+	.max_read_len = QUP_READ_LIMIT,
+};
+
 static void qup_i2c_enable_clocks(struct qup_i2c_dev *qup)
 {
 	clk_prepare_enable(qup->clk);
@@ -670,6 +668,7 @@ static int qup_i2c_probe(struct platform_device *pdev)
 
 	i2c_set_adapdata(&qup->adap, qup);
 	qup->adap.algo = &qup_i2c_algo;
+	qup->adap.quirks = &qup_i2c_quirks;
 	qup->adap.dev.parent = qup->dev;
 	qup->adap.dev.of_node = pdev->dev.of_node;
 	strlcpy(qup->adap.name, "QUP I2C adapter", sizeof(qup->adap.name));

drivers/i2c/busses/i2c-viperboard.c

@@ -288,10 +288,6 @@ static int vprbrd_i2c_xfer(struct i2c_adapter *i2c, struct i2c_msg *msgs,
 			i, pmsg->flags & I2C_M_RD ? "read" : "write",
 			pmsg->flags, pmsg->len, pmsg->addr);
 
-		/* msgs longer than 2048 bytes are not supported by adapter */
-		if (pmsg->len > 2048)
-			return -EINVAL;
-
 		mutex_lock(&vb->lock);
 		/* directly send the message */
 		if (pmsg->flags & I2C_M_RD) {
@@ -358,6 +354,11 @@ static const struct i2c_algorithm vprbrd_algorithm = {
 	.functionality	= vprbrd_i2c_func,
 };
 
+static struct i2c_adapter_quirks vprbrd_quirks = {
+	.max_read_len = 2048,
+	.max_write_len = 2048,
+};
+
 static int vprbrd_i2c_probe(struct platform_device *pdev)
 {
 	struct vprbrd *vb = dev_get_drvdata(pdev->dev.parent);
@@ -373,6 +374,7 @@ static int vprbrd_i2c_probe(struct platform_device *pdev)
 	vb_i2c->i2c.owner = THIS_MODULE;
 	vb_i2c->i2c.class = I2C_CLASS_HWMON;
 	vb_i2c->i2c.algo = &vprbrd_algorithm;
+	vb_i2c->i2c.quirks = &vprbrd_quirks;
 	vb_i2c->i2c.algo_data = vb;
 	/* save the param in usb capabable memory */
 	vb_i2c->bus_freq_param = i2c_bus_param;

drivers/i2c/i2c-core.c

@@ -1929,6 +1929,65 @@ module_exit(i2c_exit);
  * ----------------------------------------------------
  */
 
+/* Check if val is exceeding the quirk IFF quirk is non 0 */
+#define i2c_quirk_exceeded(val, quirk) ((quirk) && ((val) > (quirk)))
+
+static int i2c_quirk_error(struct i2c_adapter *adap, struct i2c_msg *msg, char *err_msg)
+{
+	dev_err_ratelimited(&adap->dev, "adapter quirk: %s (addr 0x%04x, size %u, %s)\n",
+			    err_msg, msg->addr, msg->len,
+			    msg->flags & I2C_M_RD ? "read" : "write");
+	return -EOPNOTSUPP;
+}
+
+static int i2c_check_for_quirks(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
+{
+	const struct i2c_adapter_quirks *q = adap->quirks;
+	int max_num = q->max_num_msgs, i;
+	bool do_len_check = true;
+
+	if (q->flags & I2C_AQ_COMB) {
+		max_num = 2;
+
+		/* special checks for combined messages */
+		if (num == 2) {
+			if (q->flags & I2C_AQ_COMB_WRITE_FIRST && msgs[0].flags & I2C_M_RD)
+				return i2c_quirk_error(adap, &msgs[0], "1st comb msg must be write");
+
+			if (q->flags & I2C_AQ_COMB_READ_SECOND && !(msgs[1].flags & I2C_M_RD))
+				return i2c_quirk_error(adap, &msgs[1], "2nd comb msg must be read");
+
+			if (q->flags & I2C_AQ_COMB_SAME_ADDR && msgs[0].addr != msgs[1].addr)
+				return i2c_quirk_error(adap, &msgs[0], "comb msg only to same addr");
+
+			if (i2c_quirk_exceeded(msgs[0].len, q->max_comb_1st_msg_len))
+				return i2c_quirk_error(adap, &msgs[0], "msg too long");
+
+			if (i2c_quirk_exceeded(msgs[1].len, q->max_comb_2nd_msg_len))
+				return i2c_quirk_error(adap, &msgs[1], "msg too long");
+
+			do_len_check = false;
+		}
+	}
+
+	if (i2c_quirk_exceeded(num, max_num))
+		return i2c_quirk_error(adap, &msgs[0], "too many messages");
+
+	for (i = 0; i < num; i++) {
+		u16 len = msgs[i].len;
+
+		if (msgs[i].flags & I2C_M_RD) {
+			if (do_len_check && i2c_quirk_exceeded(len, q->max_read_len))
+				return i2c_quirk_error(adap, &msgs[i], "msg too long");
+		} else {
+			if (do_len_check && i2c_quirk_exceeded(len, q->max_write_len))
+				return i2c_quirk_error(adap, &msgs[i], "msg too long");
+		}
+	}
+
+	return 0;
+}
+
 /**
  * __i2c_transfer - unlocked flavor of i2c_transfer
  * @adap: Handle to I2C bus
@@ -1946,6 +2005,9 @@ int __i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
 	unsigned long orig_jiffies;
 	int ret, try;
 
+	if (adap->quirks && i2c_check_for_quirks(adap, msgs, num))
+		return -EOPNOTSUPP;
+
 	/* i2c_trace_msg gets enabled when tracepoint i2c_transfer gets
 	 * enabled.  This is an efficient way of keeping the for-loop from
 	 * being executed when not needed.

include/linux/i2c.h

@@ -449,6 +449,48 @@ int i2c_recover_bus(struct i2c_adapter *adap);
 int i2c_generic_gpio_recovery(struct i2c_adapter *adap);
 int i2c_generic_scl_recovery(struct i2c_adapter *adap);
 
+/**
+ * struct i2c_adapter_quirks - describe flaws of an i2c adapter
+ * @flags: see I2C_AQ_* for possible flags and read below
+ * @max_num_msgs: maximum number of messages per transfer
+ * @max_write_len: maximum length of a write message
+ * @max_read_len: maximum length of a read message
+ * @max_comb_1st_msg_len: maximum length of the first msg in a combined message
+ * @max_comb_2nd_msg_len: maximum length of the second msg in a combined message
+ *
+ * Note about combined messages: Some I2C controllers can only send one message
+ * per transfer, plus something called combined message or write-then-read.
+ * This is (usually) a small write message followed by a read message and
+ * barely enough to access register based devices like EEPROMs. There is a flag
+ * to support this mode. It implies max_num_msg = 2 and does the length checks
+ * with max_comb_*_len because combined message mode usually has its own
+ * limitations. Because of HW implementations, some controllers can actually do
+ * write-then-anything or other variants. To support that, write-then-read has
+ * been broken out into smaller bits like write-first and read-second which can
+ * be combined as needed.
+ */
+
+struct i2c_adapter_quirks {
+	u64 flags;
+	int max_num_msgs;
+	u16 max_write_len;
+	u16 max_read_len;
+	u16 max_comb_1st_msg_len;
+	u16 max_comb_2nd_msg_len;
+};
+
+/* enforce max_num_msgs = 2 and use max_comb_*_len for length checks */
+#define I2C_AQ_COMB			BIT(0)
+/* first combined message must be write */
+#define I2C_AQ_COMB_WRITE_FIRST		BIT(1)
+/* second combined message must be read */
+#define I2C_AQ_COMB_READ_SECOND		BIT(2)
+/* both combined messages must have the same target address */
+#define I2C_AQ_COMB_SAME_ADDR		BIT(3)
+/* convenience macro for typical write-then read case */
+#define I2C_AQ_COMB_WRITE_THEN_READ	(I2C_AQ_COMB | I2C_AQ_COMB_WRITE_FIRST | \
+					 I2C_AQ_COMB_READ_SECOND | I2C_AQ_COMB_SAME_ADDR)
+
 /*
  * i2c_adapter is the structure used to identify a physical i2c bus along
  * with the access algorithms necessary to access it.
@@ -474,6 +516,7 @@ struct i2c_adapter {
 	struct list_head userspace_clients;
 
 	struct i2c_bus_recovery_info *bus_recovery_info;
+	const struct i2c_adapter_quirks *quirks;
 };
 #define to_i2c_adapter(d) container_of(d, struct i2c_adapter, dev)