i2c: pasemi: Improve timeout handling and error recovery

The hardware (supposedly) has a 25ms timeout for clock stretching, but
the driver uses a 10ms timeout, which is too low (and actually gets hit
with the tipd controllers on Apple Silicon machines sporadically).

Increase the timeout to 100ms, which should be plenty, and then add
handling for all the missing error condition, and better recovery in
pasemi_smb_clear(). Since this needs a bunch more bit defines, take
the change to switch to bitfield.h macros, which is much more readable.

Signed-off-by: Hector Martin <marcan@marcan.st>

Author: marcan

drivers/i2c/busses/i2c-pasemi-core.c

@@ -5,6 +5,7 @@
  * SMBus host driver for PA Semi PWRficient
  */
 
+#include <linux/bitfield.h>
 #include <linux/module.h>
 #include <linux/pci.h>
 #include <linux/kernel.h>
@@ -26,21 +27,31 @@
 #define REG_REV		0x28
 
 /* Register defs */
-#define MTXFIFO_READ	0x00000400
-#define MTXFIFO_STOP	0x00000200
-#define MTXFIFO_START	0x00000100
-#define MTXFIFO_DATA_M	0x000000ff
-
-#define MRXFIFO_EMPTY	0x00000100
-#define MRXFIFO_DATA_M	0x000000ff
-
-#define SMSTA_XEN	0x08000000
-#define SMSTA_MTN	0x00200000
-
-#define CTL_MRR		0x00000400
-#define CTL_MTR		0x00000200
-#define CTL_EN		0x00000800
-#define CTL_CLK_M	0x000000ff
+#define MTXFIFO_READ	BIT(10)
+#define MTXFIFO_STOP	BIT(9)
+#define MTXFIFO_START	BIT(8)
+#define MTXFIFO_DATA_M	GENMASK(7, 0)
+
+#define MRXFIFO_EMPTY	BIT(8)
+#define MRXFIFO_DATA_M	GENMASK(7, 0)
+
+#define SMSTA_XIP	BIT(28)
+#define SMSTA_XEN	BIT(27)
+#define SMSTA_JMD	BIT(25)
+#define SMSTA_JAM	BIT(24)
+#define SMSTA_MTO	BIT(23)
+#define SMSTA_MTA	BIT(22)
+#define SMSTA_MTN	BIT(21)
+#define SMSTA_MRNE	BIT(19)
+#define SMSTA_MTE	BIT(16)
+#define SMSTA_TOM	BIT(6)
+
+#define CTL_EN		BIT(11)
+#define CTL_MRR		BIT(10)
+#define CTL_MTR		BIT(9)
+#define CTL_CLK_M	GENMASK(7, 0)
+
+#define TRANSFER_TIMEOUT_MS	100
 
 static inline void reg_write(struct pasemi_smbus *smbus, int reg, int val)
 {
@@ -70,23 +81,45 @@ static void pasemi_reset(struct pasemi_smbus *smbus)
 	reinit_completion(&smbus->irq_completion);
 }
 
-static void pasemi_smb_clear(struct pasemi_smbus *smbus)
+static int pasemi_smb_clear(struct pasemi_smbus *smbus)
 {
 	unsigned int status;
+	int timeout = TRANSFER_TIMEOUT_MS;
 
 	status = reg_read(smbus, REG_SMSTA);
+
+	/* First wait for the bus to go idle */
+	while ((status & (SMSTA_XIP | SMSTA_JAM)) && timeout--) {
+		msleep(1);
+		status = reg_read(smbus, REG_SMSTA);
+	}
+
+	if (timeout < 0) {
+		dev_warn(smbus->dev, "Bus is still stuck (status 0x%08x)\n", status);
+		return -EIO;
+	}
+
+	/* If any badness happened or there is data in the FIFOs, reset the FIFOs */
+	if ((status & (SMSTA_MRNE | SMSTA_JMD | SMSTA_MTO | SMSTA_TOM | SMSTA_MTN | SMSTA_MTA)) ||
+		!(status & SMSTA_MTE))
+		pasemi_reset(smbus);
+
+	/* Clear the flags */
 	reg_write(smbus, REG_SMSTA, status);
+
+	return 0;
 }
 
 static int pasemi_smb_waitready(struct pasemi_smbus *smbus)
 {
-	int timeout = 100;
+	int timeout = TRANSFER_TIMEOUT_MS;
 	unsigned int status;
 
 	if (smbus->use_irq) {
 		reinit_completion(&smbus->irq_completion);
-		reg_write(smbus, REG_IMASK, SMSTA_XEN | SMSTA_MTN);
-		wait_for_completion_timeout(&smbus->irq_completion, msecs_to_jiffies(100));
+		/* XEN should be set when a transaction terminates, whether due to error or not */
+		reg_write(smbus, REG_IMASK, SMSTA_XEN);
+		wait_for_completion_timeout(&smbus->irq_completion, msecs_to_jiffies(timeout));
 		reg_write(smbus, REG_IMASK, 0);
 		status = reg_read(smbus, REG_SMSTA);
 	} else {
@@ -97,16 +130,32 @@ static int pasemi_smb_waitready(struct pasemi_smbus *smbus)
 		}
 	}
 
-	/* Got NACK? */
-	if (status & SMSTA_MTN)
-		return -ENXIO;
+	/* Controller timeout? */
+	if (status & SMSTA_TOM) {
+		dev_warn(smbus->dev, "Controller timeout, status 0x%08x\n", status);
+		return -EIO;
+	}
 
-	if (timeout < 0) {
-		dev_warn(smbus->dev, "Timeout, status 0x%08x\n", status);
-		reg_write(smbus, REG_SMSTA, status);
+	/* Peripheral timeout? */
+	if (status & SMSTA_MTO) {
+		dev_warn(smbus->dev, "Peripheral timeout, status 0x%08x\n", status);
 		return -ETIME;
 	}
 
+	/* Still stuck in a transaction? */
+	if (status & SMSTA_XIP) {
+		dev_warn(smbus->dev, "Bus stuck, status 0x%08x\n", status);
+		return -EIO;
+	}
+
+	/* Arbitration loss? */
+	if (status & SMSTA_MTA)
+		return -EBUSY;
+
+	/* Got NACK? */
+	if (status & SMSTA_MTN)
+		return -ENXIO;
+
 	/* Clear XEN */
 	reg_write(smbus, REG_SMSTA, SMSTA_XEN);
 
@@ -167,7 +216,8 @@ static int pasemi_i2c_xfer(struct i2c_adapter *adapter,
 	struct pasemi_smbus *smbus = adapter->algo_data;
 	int ret, i;
 
-	pasemi_smb_clear(smbus);
+	if (pasemi_smb_clear(smbus))
+		return -EIO;
 
 	ret = 0;
 
@@ -190,7 +240,8 @@ static int pasemi_smb_xfer(struct i2c_adapter *adapter,
 	addr <<= 1;
 	read_flag = read_write == I2C_SMBUS_READ;
 
-	pasemi_smb_clear(smbus);
+	if (pasemi_smb_clear(smbus))
+		return -EIO;
 
 	switch (size) {
 	case I2C_SMBUS_QUICK: