[U-Boot] [PATCH] mxs: i2c: Implement algorithm to set up arbitrary i2c speed

[Marek Vasut]

This algorithm computes the values of TIMING{0,1,2} registers for the
MX28 I2C block. This algorithm was derived by using a scope, but the
result seems correct.

The resulting values programmed into the registers do not correlate
with the contents of the datasheet. When using the values from the
datasheet, the I2C clock were completely wrong.

Signed-off-by: Marek Vasut <marex at denx.de>
Cc: Stefano Babic <sbabic at denx.de>
Cc: Heiko Schocher <hs at denx.de>
Cc: Fabio Estevam <fabio.estevam at freescale.com>
---
 drivers/i2c/mxs_i2c.c |   73 ++++++++++++++-----------------------------------
 1 file changed, 21 insertions(+), 52 deletions(-)

NOTE: Heiko, please apply it onto your u-boot-i2c tree, it's dependent on the
patches that are already there.

diff --git a/drivers/i2c/mxs_i2c.c b/drivers/i2c/mxs_i2c.c
index 006fb91..7b3eec5 100644
--- a/drivers/i2c/mxs_i2c.c
+++ b/drivers/i2c/mxs_i2c.c
@@ -28,6 +28,7 @@
 
 #include <common.h>
 #include <malloc.h>
+#include <i2c.h>
 #include <asm/errno.h>
 #include <asm/io.h>
 #include <asm/arch/clock.h>
@@ -40,6 +41,7 @@ void mxs_i2c_reset(void)
 {
 	struct mxs_i2c_regs *i2c_regs = (struct mxs_i2c_regs *)MXS_I2C0_BASE;
 	int ret;
+	int speed = i2c_get_bus_speed();
 
 	ret = mxs_reset_block(&i2c_regs->hw_i2c_ctrl0_reg);
 	if (ret) {
@@ -53,6 +55,8 @@ void mxs_i2c_reset(void)
 		&i2c_regs->hw_i2c_ctrl1_clr);
 
 	writel(I2C_QUEUECTRL_PIO_QUEUE_MODE, &i2c_regs->hw_i2c_queuectrl_set);
+
+	i2c_set_bus_speed(speed);
 }
 
 void mxs_i2c_setup_read(uint8_t chip, int len)
@@ -210,62 +214,28 @@ int i2c_probe(uchar chip)
 	return ret;
 }
 
-static struct mxs_i2c_speed_table {
-	uint32_t	speed;
-	uint32_t	timing0;
-	uint32_t	timing1;
-} mxs_i2c_tbl[] = {
-	{
-		100000,
-		(0x0078 << I2C_TIMING0_HIGH_COUNT_OFFSET) |
-		(0x0030 << I2C_TIMING0_RCV_COUNT_OFFSET),
-		(0x0080 << I2C_TIMING1_LOW_COUNT_OFFSET) |
-		(0x0030 << I2C_TIMING1_XMIT_COUNT_OFFSET)
-	},
-	{
-		400000,
-		(0x000f << I2C_TIMING0_HIGH_COUNT_OFFSET) |
-		(0x0007 << I2C_TIMING0_RCV_COUNT_OFFSET),
-		(0x001f << I2C_TIMING1_LOW_COUNT_OFFSET) |
-		(0x000f << I2C_TIMING1_XMIT_COUNT_OFFSET),
-	}
-};
-
-static struct mxs_i2c_speed_table *mxs_i2c_speed_to_cfg(uint32_t speed)
-{
-	int i;
-	for (i = 0; i < ARRAY_SIZE(mxs_i2c_tbl); i++)
-		if (mxs_i2c_tbl[i].speed == speed)
-			return &mxs_i2c_tbl[i];
-	return NULL;
-}
-
-static uint32_t mxs_i2c_cfg_to_speed(uint32_t timing0, uint32_t timing1)
-{
-	int i;
-	for (i = 0; i < ARRAY_SIZE(mxs_i2c_tbl); i++) {
-		if (mxs_i2c_tbl[i].timing0 != timing0)
-			continue;
-		if (mxs_i2c_tbl[i].timing1 != timing1)
-			continue;
-		return mxs_i2c_tbl[i].speed;
-	}
-
-	return 0;
-}
-
 int i2c_set_bus_speed(unsigned int speed)
 {
 	struct mxs_i2c_regs *i2c_regs = (struct mxs_i2c_regs *)MXS_I2C0_BASE;
-	struct mxs_i2c_speed_table *spd = mxs_i2c_speed_to_cfg(speed);
 
-	if (!spd) {
-		printf("MXS I2C: Invalid speed selected (%d Hz)\n", speed);
+	uint32_t base = ((24000000 / speed) - 38) / 2;
+	uint16_t high_count = base + 3;
+	uint16_t low_count = base - 3;
+	uint16_t rcv_count = (high_count * 3) / 4;
+	uint16_t xmit_count = low_count / 4;
+
+	if (speed > 540000) {
+		printf("MXS I2C: Speed too high (%d Hz)\n", speed);
+		return -EINVAL;
+	}
+
+	if (speed < 12000) {
+		printf("MXS I2C: Speed too low (%d Hz)\n", speed);
 		return -EINVAL;
 	}
 
-	writel(spd->timing0, &i2c_regs->hw_i2c_timing0);
-	writel(spd->timing1, &i2c_regs->hw_i2c_timing1);
+	writel((high_count << 16) | rcv_count, &i2c_regs->hw_i2c_timing0);
+	writel((low_count << 16) | xmit_count, &i2c_regs->hw_i2c_timing1);
 
 	writel((0x0030 << I2C_TIMING2_BUS_FREE_OFFSET) |
 		(0x0030 << I2C_TIMING2_LEADIN_COUNT_OFFSET),
@@ -277,12 +247,11 @@ int i2c_set_bus_speed(unsigned int speed)
 unsigned int i2c_get_bus_speed(void)
 {
 	struct mxs_i2c_regs *i2c_regs = (struct mxs_i2c_regs *)MXS_I2C0_BASE;
-	uint32_t timing0, timing1;
+	uint32_t timing0;
 
 	timing0 = readl(&i2c_regs->hw_i2c_timing0);
-	timing1 = readl(&i2c_regs->hw_i2c_timing1);
 
-	return mxs_i2c_cfg_to_speed(timing0, timing1);
+	return 24000000 / ((((timing0 >> 16) - 3) * 2) + 38);
 }
 
 void i2c_init(int speed, int slaveadd)
-- 
1.7.10.4