i2c: bcm2835: Set clock-stretch timeout to 35ms

The BCM2835 I2C blocks have a register to set the clock-stretch
timeout - how long the device is allowed to hold SCL low - in bus
cycles. The current driver doesn't write to the register, therefore
the default value of 64 cycles is being used for all devices.

Set the timeout to the value recommended for SMBus - 35ms.

See: #3064

Signed-off-by: Phil Elwell <[email protected]>

i2c: bcm2835: Make clock-stretch timeout configurable

The default clock-stretch timeout is 35 mS, which works well for
SMBus, but there are some I2C devices which can stretch the clock even
longer. Rather than trying to prescribe a safe default for everyone,
allow the timeout to be configured.

Signed-off-by: Alex Crawford <raspberrypi/[email protected]>

i2c-bcm2835: Flush FIFOs cleanly on error

On error condition, note the error return code, but still
handle the FIFOs in the normal way rather than relying on
C_CLEAR flushing everything cleanly.

Signed-off-by: Dave Stevenson <[email protected]>

i2c-bcm2835: Do not abort transfers on ERR if still active

If a transaction is aborted immediately on ERR being reported,
then the bus is not returned to the STOP condition, and devices
generally get very upset.

Handle the ERR and CLKT conditions only when TA is not set.

Signed-off-by: Dave Stevenson <[email protected]>

i2c-bcm2835: Implement I2C_M_IGNORE_NAK

Now that transfers aren't aborted immediately (and uncleanly) on
errors, and the FIFOs are always drained after all transfers, we
can implement I2C_M_IGNORE_NAK by ignoring the returned error
value.

Signed-off-by: Dave Stevenson <[email protected]>

Author: Phil Elwell

drivers/i2c/busses/i2c-bcm2835.c

@@ -60,6 +60,10 @@ static unsigned int debug;
 module_param(debug, uint, 0644);
 MODULE_PARM_DESC(debug, "1=err, 2=isr, 3=xfer");
 
+static unsigned int clk_tout_ms = 35; /* SMBUs-recommended 35ms */
+module_param(clk_tout_ms, uint, 0644);
+MODULE_PARM_DESC(clk_tout_ms, "clock-stretch timeout (mS)");
+
 #define BCM2835_DEBUG_MAX	512
 struct bcm2835_debug {
 	struct i2c_msg *msg;
@@ -193,6 +197,7 @@ static int clk_bcm2835_i2c_set_rate(struct clk_hw *hw, unsigned long rate,
 {
 	struct clk_bcm2835_i2c *div = to_clk_bcm2835_i2c(hw);
 	u32 redl, fedl;
+	u32 clk_tout;
 	u32 divider = clk_bcm2835_i2c_calc_divider(rate, parent_rate);
 
 	if (divider == -EINVAL)
@@ -216,6 +221,17 @@ static int clk_bcm2835_i2c_set_rate(struct clk_hw *hw, unsigned long rate,
 	bcm2835_i2c_writel(div->i2c_dev, BCM2835_I2C_DEL,
 			   (fedl << BCM2835_I2C_FEDL_SHIFT) |
 			   (redl << BCM2835_I2C_REDL_SHIFT));
+
+	/*
+	 * Set the clock stretch timeout.
+	 */
+	if (rate > 0xffff*1000/clk_tout_ms)
+	    clk_tout = 0xffff;
+	else
+	    clk_tout = clk_tout_ms*rate/1000;
+
+	bcm2835_i2c_writel(div->i2c_dev, BCM2835_I2C_CLKT, clk_tout);
+
 	return 0;
 }
 
@@ -369,10 +385,8 @@ static irqreturn_t bcm2835_i2c_isr(int this_irq, void *data)
 	bcm2835_debug_add(i2c_dev, val);
 
 	err = val & (BCM2835_I2C_S_CLKT | BCM2835_I2C_S_ERR);
-	if (err) {
+	if (err && !(val & BCM2835_I2C_S_TA))
 		i2c_dev->msg_err = err;
-		goto complete;
-	}
 
 	if (val & BCM2835_I2C_S_DONE) {
 		if (!i2c_dev->curr_msg) {
@@ -384,8 +398,6 @@ static irqreturn_t bcm2835_i2c_isr(int this_irq, void *data)
 
 		if ((val & BCM2835_I2C_S_RXD) || i2c_dev->msg_buf_remaining)
 			i2c_dev->msg_err = BCM2835_I2C_S_LEN;
-		else
-			i2c_dev->msg_err = 0;
 		goto complete;
 	}
 
@@ -431,6 +443,7 @@ static int bcm2835_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[],
 {
 	struct bcm2835_i2c_dev *i2c_dev = i2c_get_adapdata(adap);
 	unsigned long time_left;
+	bool ignore_nak = false;
 	int i;
 
 	if (debug)
@@ -440,15 +453,19 @@ static int bcm2835_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[],
 		for (i = 0; i < num; i++)
 			bcm2835_debug_print_msg(i2c_dev, &msgs[i], i + 1, num, __func__);
 
-	for (i = 0; i < (num - 1); i++)
+	for (i = 0; i < (num - 1); i++) {
 		if (msgs[i].flags & I2C_M_RD) {
 			dev_warn_once(i2c_dev->dev,
 				      "only one read message supported, has to be last\n");
 			return -EOPNOTSUPP;
 		}
+		if (msgs[i].flags & I2C_M_IGNORE_NAK)
+			ignore_nak = true;
+	}
 
 	i2c_dev->curr_msg = msgs;
 	i2c_dev->num_msgs = num;
+	i2c_dev->msg_err = 0;
 	reinit_completion(&i2c_dev->completion);
 
 	bcm2835_i2c_start_transfer(i2c_dev);
@@ -458,6 +475,9 @@ static int bcm2835_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[],
 
 	bcm2835_i2c_finish_transfer(i2c_dev);
 
+	if (ignore_nak)
+		i2c_dev->msg_err &= ~BCM2835_I2C_S_ERR;
+
 	if (debug > 1 || (debug && (!time_left || i2c_dev->msg_err)))
 		bcm2835_debug_print(i2c_dev);
 	i2c_dev->debug_num_msgs = 0;
@@ -483,7 +503,7 @@ static int bcm2835_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[],
 
 static u32 bcm2835_i2c_func(struct i2c_adapter *adap)
 {
-	return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL;
+	return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL | I2C_FUNC_PROTOCOL_MANGLING;
 }
 
 static const struct i2c_algorithm bcm2835_i2c_algo = {