i2c: fix i2c-sh_mobile timing issues

This patch teaches the i2c-sh_mobile driver to make use of wait irqs.
Without this patch only dte irqs are used which may lead to overruns
and cases of missing stop and extra bytes being read on the i2c bus.

Use of wait irqs forces the hardware to pause and wait until the cpu
is ready. Polling is also reworked in this patch to fix ms delay issues.

Verified with bus analyzer and tested on MigoR and AP325RXA boards.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

drivers/i2c/busses/i2c-sh_mobile.c

@@ -31,13 +31,84 @@
 #include <linux/clk.h>
 #include <linux/io.h>
 
+/* Transmit operation:                                                      */
+/*                                                                          */
+/* 0 byte transmit                                                          */
+/* BUS:     S     A8     ACK   P                                            */
+/* IRQ:       DTE   WAIT                                                    */
+/* ICIC:                                                                    */
+/* ICCR: 0x94 0x90                                                          */
+/* ICDR:      A8                                                            */
+/*                                                                          */
+/* 1 byte transmit                                                          */
+/* BUS:     S     A8     ACK   D8(1)   ACK   P                              */
+/* IRQ:       DTE   WAIT         WAIT                                       */
+/* ICIC:      -DTE                                                          */
+/* ICCR: 0x94       0x90                                                    */
+/* ICDR:      A8    D8(1)                                                   */
+/*                                                                          */
+/* 2 byte transmit                                                          */
+/* BUS:     S     A8     ACK   D8(1)   ACK   D8(2)   ACK   P                */
+/* IRQ:       DTE   WAIT         WAIT          WAIT                         */
+/* ICIC:      -DTE                                                          */
+/* ICCR: 0x94                    0x90                                       */
+/* ICDR:      A8    D8(1)        D8(2)                                      */
+/*                                                                          */
+/* 3 bytes or more, +---------+ gets repeated                               */
+/*                                                                          */
+/*                                                                          */
+/* Receive operation:                                                       */
+/*                                                                          */
+/* 0 byte receive - not supported since slave may hold SDA low              */
+/*                                                                          */
+/* 1 byte receive       [TX] | [RX]                                         */
+/* BUS:     S     A8     ACK | D8(1)   ACK   P                              */
+/* IRQ:       DTE   WAIT     |   WAIT     DTE                               */
+/* ICIC:      -DTE           |   +DTE                                       */
+/* ICCR: 0x94       0x81     |   0xc0                                       */
+/* ICDR:      A8             |            D8(1)                             */
+/*                                                                          */
+/* 2 byte receive        [TX]| [RX]                                         */
+/* BUS:     S     A8     ACK | D8(1)   ACK   D8(2)   ACK   P                */
+/* IRQ:       DTE   WAIT     |   WAIT          WAIT     DTE                 */
+/* ICIC:      -DTE           |                 +DTE                         */
+/* ICCR: 0x94       0x81     |                 0xc0                         */
+/* ICDR:      A8             |                 D8(1)    D8(2)               */
+/*                                                                          */
+/* 3 byte receive       [TX] | [RX]                                         */
+/* BUS:     S     A8     ACK | D8(1)   ACK   D8(2)   ACK   D8(3)   ACK    P */
+/* IRQ:       DTE   WAIT     |   WAIT          WAIT         WAIT      DTE   */
+/* ICIC:      -DTE           |                              +DTE            */
+/* ICCR: 0x94       0x81     |                              0xc0            */
+/* ICDR:      A8             |                 D8(1)        D8(2)     D8(3) */
+/*                                                                          */
+/* 4 bytes or more, this part is repeated    +---------+                    */
+/*                                                                          */
+/*                                                                          */
+/* Interrupt order and BUSY flag                                            */
+/*     ___                                                 _                */
+/* SDA ___\___XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXAAAAAAAAA___/                 */
+/* SCL      \_/1\_/2\_/3\_/4\_/5\_/6\_/7\_/8\___/9\_____/                   */
+/*                                                                          */
+/*        S   D7  D6  D5  D4  D3  D2  D1  D0              P                 */
+/*                                           ___                            */
+/* WAIT IRQ ________________________________/   \___________                */
+/* TACK IRQ ____________________________________/   \_______                */
+/* DTE  IRQ __________________________________________/   \_                */
+/* AL   IRQ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX                */
+/*         _______________________________________________                  */
+/* BUSY __/                                               \_                */
+/*                                                                          */
+
 enum sh_mobile_i2c_op {
 	OP_START = 0,
-	OP_TX_ONLY,
+	OP_TX_FIRST,
+	OP_TX,
 	OP_TX_STOP,
 	OP_TX_TO_RX,
-	OP_RX_ONLY,
+	OP_RX,
 	OP_RX_STOP,
+	OP_RX_STOP_DATA,
 };
 
 struct sh_mobile_i2c_data {
@@ -127,25 +198,34 @@ static unsigned char i2c_op(struct sh_mobile_i2c_data *pd,
 	spin_lock_irqsave(&pd->lock, flags);
 
 	switch (op) {
-	case OP_START:
+	case OP_START: /* issue start and trigger DTE interrupt */
 		iowrite8(0x94, ICCR(pd));
 		break;
-	case OP_TX_ONLY:
+	case OP_TX_FIRST: /* disable DTE interrupt and write data */
+		iowrite8(ICIC_WAITE | ICIC_ALE | ICIC_TACKE, ICIC(pd));
 		iowrite8(data, ICDR(pd));
 		break;
-	case OP_TX_STOP:
+	case OP_TX: /* write data */
 		iowrite8(data, ICDR(pd));
-		iowrite8(0x90, ICCR(pd));
-		iowrite8(ICIC_ALE | ICIC_TACKE, ICIC(pd));
 		break;
-	case OP_TX_TO_RX:
+	case OP_TX_STOP: /* write data and issue a stop afterwards */
 		iowrite8(data, ICDR(pd));
+		iowrite8(0x90, ICCR(pd));
+		break;
+	case OP_TX_TO_RX: /* select read mode */
 		iowrite8(0x81, ICCR(pd));
 		break;
-	case OP_RX_ONLY:
+	case OP_RX: /* just read data */
 		ret = ioread8(ICDR(pd));
 		break;
-	case OP_RX_STOP:
+	case OP_RX_STOP: /* enable DTE interrupt, issue stop */
+		iowrite8(ICIC_DTEE | ICIC_WAITE | ICIC_ALE | ICIC_TACKE,
+			 ICIC(pd));
+		iowrite8(0xc0, ICCR(pd));
+		break;
+	case OP_RX_STOP_DATA: /* enable DTE interrupt, read data, issue stop */
+		iowrite8(ICIC_DTEE | ICIC_WAITE | ICIC_ALE | ICIC_TACKE,
+			 ICIC(pd));
 		ret = ioread8(ICDR(pd));
 		iowrite8(0xc0, ICCR(pd));
 		break;
@@ -157,58 +237,120 @@ static unsigned char i2c_op(struct sh_mobile_i2c_data *pd,
 	return ret;
 }
 
+static int sh_mobile_i2c_is_first_byte(struct sh_mobile_i2c_data *pd)
+{
+	if (pd->pos == -1)
+		return 1;
+
+	return 0;
+}
+
+static int sh_mobile_i2c_is_last_byte(struct sh_mobile_i2c_data *pd)
+{
+	if (pd->pos == (pd->msg->len - 1))
+		return 1;
+
+	return 0;
+}
+
+static void sh_mobile_i2c_get_data(struct sh_mobile_i2c_data *pd,
+				   unsigned char *buf)
+{
+	switch (pd->pos) {
+	case -1:
+		*buf = (pd->msg->addr & 0x7f) << 1;
+		*buf |= (pd->msg->flags & I2C_M_RD) ? 1 : 0;
+		break;
+	default:
+		*buf = pd->msg->buf[pd->pos];
+	}
+}
+
+static int sh_mobile_i2c_isr_tx(struct sh_mobile_i2c_data *pd)
+{
+	unsigned char data;
+
+	if (pd->pos == pd->msg->len)
+		return 1;
+
+	sh_mobile_i2c_get_data(pd, &data);
+
+	if (sh_mobile_i2c_is_last_byte(pd))
+		i2c_op(pd, OP_TX_STOP, data);
+	else if (sh_mobile_i2c_is_first_byte(pd))
+		i2c_op(pd, OP_TX_FIRST, data);
+	else
+		i2c_op(pd, OP_TX, data);
+
+	pd->pos++;
+	return 0;
+}
+
+static int sh_mobile_i2c_isr_rx(struct sh_mobile_i2c_data *pd)
+{
+	unsigned char data;
+	int real_pos;
+
+	do {
+		if (pd->pos <= -1) {
+			sh_mobile_i2c_get_data(pd, &data);
+
+			if (sh_mobile_i2c_is_first_byte(pd))
+				i2c_op(pd, OP_TX_FIRST, data);
+			else
+				i2c_op(pd, OP_TX, data);
+			break;
+		}
+
+		if (pd->pos == 0) {
+			i2c_op(pd, OP_TX_TO_RX, 0);
+			break;
+		}
+
+		real_pos = pd->pos - 2;
+
+		if (pd->pos == pd->msg->len) {
+			if (real_pos < 0) {
+				i2c_op(pd, OP_RX_STOP, 0);
+				break;
+			}
+			data = i2c_op(pd, OP_RX_STOP_DATA, 0);
+		} else
+			data = i2c_op(pd, OP_RX, 0);
+
+		pd->msg->buf[real_pos] = data;
+	} while (0);
+
+	pd->pos++;
+	return pd->pos == (pd->msg->len + 2);
+}
+
 static irqreturn_t sh_mobile_i2c_isr(int irq, void *dev_id)
 {
 	struct platform_device *dev = dev_id;
 	struct sh_mobile_i2c_data *pd = platform_get_drvdata(dev);
-	struct i2c_msg *msg = pd->msg;
-	unsigned char data, sr;
-	int wakeup = 0;
+	unsigned char sr;
+	int wakeup;
 
 	sr = ioread8(ICSR(pd));
-	pd->sr |= sr;
+	pd->sr |= sr; /* remember state */
 
 	dev_dbg(pd->dev, "i2c_isr 0x%02x 0x%02x %s %d %d!\n", sr, pd->sr,
-	       (msg->flags & I2C_M_RD) ? "read" : "write",
-	       pd->pos, msg->len);
+	       (pd->msg->flags & I2C_M_RD) ? "read" : "write",
+	       pd->pos, pd->msg->len);
 
 	if (sr & (ICSR_AL | ICSR_TACK)) {
-		iowrite8(0, ICIC(pd)); /* disable interrupts */
-		wakeup = 1;
-		goto do_wakeup;
-	}
+		/* don't interrupt transaction - continue to issue stop */
+		iowrite8(sr & ~(ICSR_AL | ICSR_TACK), ICSR(pd));
+		wakeup = 0;
+	} else if (pd->msg->flags & I2C_M_RD)
+		wakeup = sh_mobile_i2c_isr_rx(pd);
+	else
+		wakeup = sh_mobile_i2c_isr_tx(pd);
 
-	if (pd->pos == msg->len) {
-		i2c_op(pd, OP_RX_ONLY, 0);
-		wakeup = 1;
-		goto do_wakeup;
-	}
+	if (sr & ICSR_WAIT) /* TODO: add delay here to support slow acks */
+		iowrite8(sr & ~ICSR_WAIT, ICSR(pd));
 
-	if (pd->pos == -1) {
-		data = (msg->addr & 0x7f) << 1;
-		data |= (msg->flags & I2C_M_RD) ? 1 : 0;
-	} else
-		data = msg->buf[pd->pos];
-
-	if ((pd->pos == -1) || !(msg->flags & I2C_M_RD)) {
-		if (msg->flags & I2C_M_RD)
-			i2c_op(pd, OP_TX_TO_RX, data);
-		else if (pd->pos == (msg->len - 1)) {
-			i2c_op(pd, OP_TX_STOP, data);
-			wakeup = 1;
-		} else
-			i2c_op(pd, OP_TX_ONLY, data);
-	} else {
-		if (pd->pos == (msg->len - 1))
-			data = i2c_op(pd, OP_RX_STOP, 0);
-		else
-			data = i2c_op(pd, OP_RX_ONLY, 0);
-
-		msg->buf[pd->pos] = data;
-	}
-	pd->pos++;
-
- do_wakeup:
 	if (wakeup) {
 		pd->sr |= SW_DONE;
 		wake_up(&pd->wait);
@@ -219,6 +361,11 @@ static irqreturn_t sh_mobile_i2c_isr(int irq, void *dev_id)
 
 static int start_ch(struct sh_mobile_i2c_data *pd, struct i2c_msg *usr_msg)
 {
+	if (usr_msg->len == 0 && (usr_msg->flags & I2C_M_RD)) {
+		dev_err(pd->dev, "Unsupported zero length i2c read\n");
+		return -EIO;
+	}
+
 	/* Initialize channel registers */
 	iowrite8(ioread8(ICCR(pd)) & ~ICCR_ICE, ICCR(pd));
 
@@ -233,9 +380,8 @@ static int start_ch(struct sh_mobile_i2c_data *pd, struct i2c_msg *usr_msg)
 	pd->pos = -1;
 	pd->sr = 0;
 
-	/* Enable all interrupts except wait */
-	iowrite8(ioread8(ICIC(pd)) | ICIC_ALE | ICIC_TACKE | ICIC_DTEE,
-		 ICIC(pd));
+	/* Enable all interrupts to begin with */
+	iowrite8(ICIC_WAITE | ICIC_ALE | ICIC_TACKE | ICIC_DTEE, ICIC(pd));
 	return 0;
 }
 
@@ -268,25 +414,18 @@ static int sh_mobile_i2c_xfer(struct i2c_adapter *adapter,
 		if (!k)
 			dev_err(pd->dev, "Transfer request timed out\n");
 
-		retry_count = 10;
+		retry_count = 1000;
 again:
 		val = ioread8(ICSR(pd));
 
 		dev_dbg(pd->dev, "val 0x%02x pd->sr 0x%02x\n", val, pd->sr);
 
-		if ((val | pd->sr) & (ICSR_TACK | ICSR_AL)) {
-			err = -EIO;
-			break;
-		}
-
 		/* the interrupt handler may wake us up before the
 		 * transfer is finished, so poll the hardware
 		 * until we're done.
 		 */
-
-		if (!(!(val & ICSR_BUSY) && (val & ICSR_SCLM) &&
-		      (val & ICSR_SDAM))) {
-			msleep(1);
+		if (val & ICSR_BUSY) {
+			udelay(10);
 			if (retry_count--)
 				goto again;
 
@@ -294,6 +433,12 @@ again:
 			dev_err(pd->dev, "Polling timed out\n");
 			break;
 		}
+
+		/* handle missing acknowledge and arbitration lost */
+		if ((val | pd->sr) & (ICSR_TACK | ICSR_AL)) {
+			err = -EIO;
+			break;
+		}
 	}
 
 	deactivate_ch(pd);