i2c: i2c-cdns: Implement workaround for hold quirk of the rev 1.0

Revision 1.0 of this IP has a quirk where if during a long read transfer
the transfer_size register will go to 0, the master will send a NACK to
the slave prematurely.
The way to work around this is to reprogram the transfer_size register
mid-transfer when the only the receive fifo is known full, i.e. the I2C
bus is known non-active.
The workaround is based on the implementation in the linux-kernel.

Signed-off-by: Moritz Fischer <moritz.fischer@ettus.com>
Cc: Heiko Schocher <hs@denx.de>
Cc: Michal Simek <michal.simek@xilinx.com>
Cc: u-boot@lists.denx.de

drivers/i2c/i2c-cdns.c

@@ -17,6 +17,7 @@
 #include <i2c.h>
 #include <fdtdec.h>
 #include <mapmem.h>
+#include <wait_bit.h>
 
 DECLARE_GLOBAL_DATA_PTR;
 
@@ -67,6 +68,8 @@ struct cdns_i2c_regs {
 
 #define CDNS_I2C_FIFO_DEPTH		16
 #define CDNS_I2C_TRANSFER_SIZE_MAX	255 /* Controller transfer limit */
+#define CDNS_I2C_TRANSFER_SIZE		(CDNS_I2C_TRANSFER_SIZE_MAX - 3)
+
 #define CDNS_I2C_BROKEN_HOLD_BIT	BIT(0)
 
 #ifdef DEBUG
@@ -247,15 +250,21 @@ static int cdns_i2c_write_data(struct i2c_cdns_bus *i2c_bus, u32 addr, u8 *data,
 			       u32 len)
 {
 	u8 *cur_data = data;
-
 	struct cdns_i2c_regs *regs = i2c_bus->regs;
 
+	/* Set the controller in Master transmit mode and clear FIFO */
 	setbits_le32(&regs->control, CDNS_I2C_CONTROL_CLR_FIFO);
-
-
 	clrbits_le32(&regs->control, CDNS_I2C_CONTROL_RW);
 
+	/* Check message size against FIFO depth, and set hold bus bit
+	 * if it is greater than FIFO depth
+	 */
+	if (len > CDNS_I2C_FIFO_DEPTH)
+		setbits_le32(&regs->control, CDNS_I2C_CONTROL_HOLD);
+
+	/* Clear the interrupts in status register */
 	writel(0xFF, &regs->interrupt_status);
+
 	writel(addr, &regs->address);
 
 	while (len--) {
@@ -280,48 +289,98 @@ static int cdns_i2c_write_data(struct i2c_cdns_bus *i2c_bus, u32 addr, u8 *data,
 	return 0;
 }
 
+static inline bool cdns_is_hold_quirk(int hold_quirk, int curr_recv_count)
+{
+	return hold_quirk && (curr_recv_count == CDNS_I2C_FIFO_DEPTH + 1);
+}
+
 static int cdns_i2c_read_data(struct i2c_cdns_bus *i2c_bus, u32 addr, u8 *data,
-			      u32 len)
+			      u32 recv_count)
 {
-	u32 status;
-	u32 i = 0;
 	u8 *cur_data = data;
-
-	/* TODO: Fix this */
 	struct cdns_i2c_regs *regs = i2c_bus->regs;
+	int curr_recv_count;
+	int updatetx, hold_quirk;
 
 	/* Check the hardware can handle the requested bytes */
-	if ((len < 0))
+	if ((recv_count < 0))
 		return -EINVAL;
 
+	curr_recv_count = recv_count;
+
+	/* Check for the message size against the FIFO depth */
+	if (recv_count > CDNS_I2C_FIFO_DEPTH)
+		setbits_le32(&regs->control, CDNS_I2C_CONTROL_HOLD);
+
 	setbits_le32(&regs->control, CDNS_I2C_CONTROL_CLR_FIFO |
 		CDNS_I2C_CONTROL_RW);
 
+	if (recv_count > CDNS_I2C_TRANSFER_SIZE) {
+		curr_recv_count = CDNS_I2C_TRANSFER_SIZE;
+		writel(curr_recv_count, &regs->transfer_size);
+	} else {
+		writel(recv_count, &regs->transfer_size);
+	}
+
 	/* Start reading data */
 	writel(addr, &regs->address);
-	writel(len, &regs->transfer_size);
-
-	/* Wait for data */
-	do {
-		status = cdns_i2c_wait(regs, CDNS_I2C_INTERRUPT_COMP |
-			CDNS_I2C_INTERRUPT_DATA);
-		if (!status) {
-			/* Release the bus */
-			clrbits_le32(&regs->control, CDNS_I2C_CONTROL_HOLD);
-			return -ETIMEDOUT;
+
+	updatetx = recv_count > curr_recv_count;
+
+	hold_quirk = (i2c_bus->quirks & CDNS_I2C_BROKEN_HOLD_BIT) && updatetx;
+
+	while (recv_count) {
+		while (readl(&regs->status) & CDNS_I2C_STATUS_RXDV) {
+			if (recv_count < CDNS_I2C_FIFO_DEPTH &&
+			    !i2c_bus->hold_flag) {
+				clrbits_le32(&regs->control,
+					     CDNS_I2C_CONTROL_HOLD);
+			}
+			*(cur_data)++ = readl(&regs->data);
+			recv_count--;
+			curr_recv_count--;
+
+			if (cdns_is_hold_quirk(hold_quirk, curr_recv_count))
+				break;
 		}
-		debug("Read %d bytes\n",
-		      len - readl(&regs->transfer_size));
-		for (; i < len - readl(&regs->transfer_size); i++)
-			*(cur_data++) = readl(&regs->data);
-	} while (readl(&regs->transfer_size) != 0);
-	/* All done... release the bus */
-	if (!i2c_bus->hold_flag)
-		clrbits_le32(&regs->control, CDNS_I2C_CONTROL_HOLD);
 
-#ifdef DEBUG
-	cdns_i2c_debug_status(regs);
-#endif
+		if (cdns_is_hold_quirk(hold_quirk, curr_recv_count)) {
+			/* wait while fifo is full */
+			while (readl(&regs->transfer_size) !=
+				     (curr_recv_count - CDNS_I2C_FIFO_DEPTH))
+				;
+			/*
+			 * Check number of bytes to be received against maximum
+			 * transfer size and update register accordingly.
+			 */
+			if ((recv_count - CDNS_I2C_FIFO_DEPTH) >
+			    CDNS_I2C_TRANSFER_SIZE) {
+				writel(CDNS_I2C_TRANSFER_SIZE,
+				       &regs->transfer_size);
+				curr_recv_count = CDNS_I2C_TRANSFER_SIZE +
+					CDNS_I2C_FIFO_DEPTH;
+			} else {
+				writel(recv_count - CDNS_I2C_FIFO_DEPTH,
+				       &regs->transfer_size);
+				curr_recv_count = recv_count;
+			}
+		} else if (recv_count && !hold_quirk && !curr_recv_count) {
+			writel(addr, &regs->address);
+			if (recv_count > CDNS_I2C_TRANSFER_SIZE) {
+				writel(CDNS_I2C_TRANSFER_SIZE,
+				       &regs->transfer_size);
+				curr_recv_count = CDNS_I2C_TRANSFER_SIZE;
+			} else {
+				writel(recv_count, &regs->transfer_size);
+				curr_recv_count = recv_count;
+			}
+		}
+	}
+
+	/* Wait for the address and data to be sent */
+	if (!cdns_i2c_wait(regs, CDNS_I2C_INTERRUPT_COMP))
+		return -ETIMEDOUT;
+
 	return 0;
 }