[PATCH v3 3/3] i2c: imx_lpi2c: Support read transfers longer than 256 bytes

[fedorross at gmail.com]

From: Fedor Ross <fedor.ross at ifm.com>

The TXFIFO register of LPI2C only has one byte length, and if the length
of the data that needs to be read exceeds 256 bytes, it needs to be
written to TXFIFO multiple times.

Signed-off-by: Fedor Ross <fedor.ross at ifm.com>
---
Cc: Heiko Schocher <hs at denx.de>
Cc: Tom Rini <trini at konsulko.com>
Cc: Marek Vasut <marex at denx.de>
---

Changes in v3:
- Add LPI2C_CHUNK_LEN_MIN
- Force macros LPI2C_CHUNK_DATA and LPI2C_CHUNK_LEN_MIN to be of
  unsigned type to satisfy type-check of min()/max()/clamp() macros.

Changes in v2:
- Add additional '---' below SoB line to separate Cc list. This way it
  does not get included in the commit message when the patch is applied.
- Prefix 'CHUNK_DATA' macro with 'LPI2C_' to namespace it.
- Do bit manipulation in writel() function directly and drop the 
  'val = assignment' .

 drivers/i2c/imx_lpi2c.c | 72 +++++++++++++++++++++++++++--------------
 1 file changed, 47 insertions(+), 25 deletions(-)

diff --git a/drivers/i2c/imx_lpi2c.c b/drivers/i2c/imx_lpi2c.c
index 54db6fa863f..4636da9f301 100644
--- a/drivers/i2c/imx_lpi2c.c
+++ b/drivers/i2c/imx_lpi2c.c
@@ -19,6 +19,9 @@
 #define LPI2C_NACK_TOUT_MS 1
 #define LPI2C_TIMEOUT_MS 100
 
+#define LPI2C_CHUNK_DATA	256U
+#define LPI2C_CHUNK_LEN_MIN	1U
+
 static int bus_i2c_init(struct udevice *bus);
 
 /* Weak linked function for overridden by some SoC power function */
@@ -118,8 +121,10 @@ static int bus_i2c_send(struct udevice *bus, u8 *txbuf, int len)
 
 static int bus_i2c_receive(struct udevice *bus, u8 *rxbuf, int len)
 {
+	struct dm_i2c_bus *i2c = dev_get_uclass_priv(bus);
 	struct imx_lpi2c_bus *i2c_bus = dev_get_priv(bus);
 	struct imx_lpi2c_reg *regs = (struct imx_lpi2c_reg *)(i2c_bus->base);
+	unsigned int chunk_len, rx_remain, timeout;
 	lpi2c_status_t result = LPI2C_SUCESS;
 	u32 val;
 	ulong start_time = get_timer(0);
@@ -128,33 +133,50 @@ static int bus_i2c_receive(struct udevice *bus, u8 *rxbuf, int len)
 	if (!len)
 		return result;
 
-	result = bus_i2c_wait_for_tx_ready(regs);
-	if (result) {
-		debug("i2c: receive wait for tx ready: %d\n", result);
-		return result;
-	}
+	/*
+	 * Extend the timeout for a bulk read if needed.
+	 * The calculated timeout is the result of multiplying the
+	 * transfer length with 8 bit + ACK + one clock of extra time,
+	 * considering the I2C bus frequency.
+	 */
+	timeout = max(len * 10 * 1000 / i2c->speed_hz, LPI2C_TIMEOUT_MS);
 
-	/* clear all status flags */
-	writel(0x7f00, &regs->msr);
-	/* send receive command */
-	val = LPI2C_MTDR_CMD(0x1) | LPI2C_MTDR_DATA(len - 1);
-	writel(val, &regs->mtdr);
+	rx_remain = len;
+	while (rx_remain > 0) {
+		chunk_len = clamp(rx_remain, LPI2C_CHUNK_LEN_MIN, LPI2C_CHUNK_DATA) - 1;
 
-	while (len--) {
-		do {
-			result = imx_lpci2c_check_clear_error(regs);
-			if (result) {
-				debug("i2c: receive check clear error: %d\n",
-				      result);
-				return result;
-			}
-			if (get_timer(start_time) > LPI2C_TIMEOUT_MS) {
-				debug("i2c: receive mrdr: timeout\n");
-				return -1;
-			}
-			val = readl(&regs->mrdr);
-		} while (val & LPI2C_MRDR_RXEMPTY_MASK);
-		*rxbuf++ = LPI2C_MRDR_DATA(val);
+		result = bus_i2c_wait_for_tx_ready(regs);
+		if (result) {
+			debug("i2c: receive wait for tx ready: %d\n", result);
+			return result;
+		}
+
+		/* clear all status flags */
+		writel(0x7f00, &regs->msr);
+		/* send receive command */
+		writel(LPI2C_MTDR_CMD(0x1) | LPI2C_MTDR_DATA(chunk_len), &regs->mtdr);
+		rx_remain = rx_remain - (chunk_len & 0xff) - 1;
+
+		while (len--) {
+			do {
+				result = imx_lpci2c_check_clear_error(regs);
+				if (result) {
+					debug("i2c: receive check clear error: %d\n",
+					      result);
+					return result;
+				}
+				if (get_timer(start_time) > timeout) {
+					debug("i2c: receive mrdr: timeout\n");
+					return -1;
+				}
+				val = readl(&regs->mrdr);
+			} while (val & LPI2C_MRDR_RXEMPTY_MASK);
+			*rxbuf++ = LPI2C_MRDR_DATA(val);
+
+			/* send next receive command before controller NACKs last byte */
+			if ((len - rx_remain) < 2 && rx_remain > 0)
+				break;
+		}
 	}
 
 	return result;
-- 
2.34.1