[U-Boot] [PATCH 1/4] OMAP3 I2C Fix the sampling clock.

[Tom Rix]

This problem is seen on Zoom1 and Zoom2 in the startup and
when i2c probe is used

Before :

In:    serial
Out:   serial
Err:   serial
timed out in wait_for_bb: I2C_STAT=1000
timed out in wait_for_bb: I2C_STAT=1000
timed out in wait_for_bb: I2C_STAT=1000
timed out in wait_for_pin: I2C_STAT=1000
I2C read: I/O error
timed out in wait_for_bb: I2C_STAT=1000
timed out in wait_for_bb: I2C_STAT=1000
Die ID #327c00020000000004013ddd05026013
Hit any key to stop autoboot:  0
OMAP3 Zoom1# i2c probe
Valid chip addresses:timed out in wait_for_bb: I2C_STAT=1000
 02 03 04 05 06 07 08 09 0A 0B 0C 0D <snip>

After :

In:    serial
Out:   serial
Err:   serial
Die ID #327c00020000000004013ddd05026013
Hit any key to stop autoboot:  0
OMAP3 Zoom1# i2c probe
Valid chip addresses: 48 49 4A 4B

The addresses are for the twl4030.

The prescalar that converts the function clock to the sampling
clock is hardcoded to 0.  The reference manual recommends 7
if the function clock is 96MHz.

Instead of just changing the hardcoded values, the prescalar
is calculated from the value I2C_IP_CLK.

The i2c #defines are in kHz.  The speed passed into the
i2c init routine is in Hz.  To be consistent, change the
defines to be in Hz.

This was runtime verified on Zoom1, Zoom2, Beagle and Overo.
The 400kHz case was verifed on a test Zoom2 configuration.

Signed-off-by: Tom Rix <Tom.Rix at windriver.com>
---
 drivers/i2c/omap24xx_i2c.c       |   54 +++++++++++++++++++++++++++++++++-----
 include/asm-arm/arch-omap3/i2c.h |   16 +++++-----
 2 files changed, 55 insertions(+), 15 deletions(-)

diff --git a/drivers/i2c/omap24xx_i2c.c b/drivers/i2c/omap24xx_i2c.c
index 6784603..81947e6 100644
--- a/drivers/i2c/omap24xx_i2c.c
+++ b/drivers/i2c/omap24xx_i2c.c
@@ -31,7 +31,49 @@ static void flush_fifo(void);
 
 void i2c_init (int speed, int slaveadd)
 {
-	u16 scl;
+	int psc, iclk, scll, sclh;
+
+	/* Only handle standard and fast speeds */
+	if ((speed != OMAP_I2C_STANDARD) &&
+	    (speed != OMAP_I2C_FAST_MODE)) {
+		printf("Error : I2C unsupported speed %d\n", speed);
+		return;
+	}
+
+	/*
+	 * Calculate the prescalar to go from from the function clock
+	 * to the internal sampling clock, 12MHz.
+	 */
+	psc = I2C_PSC_MAX;
+	while (psc >= I2C_PSC_MIN) {
+		iclk = I2C_IP_CLK / (psc + 1);
+		if (12000000 <= iclk)
+			break;
+		psc--;
+	}
+	if (psc < I2C_PSC_MIN) {
+		printf("Error : I2C unsupported prescalar %d\n", psc);
+		return;
+	}
+
+	/*
+	 * How the low and high time periods are calculated
+	 * See the OMAP3xxx Reference Manual for more details
+	 *
+	 * tlow + thigh = 1 / speed
+	 * thigh = tlow, nice square wave..
+	 *
+	 * tlow = 1 / (2 * speed) = (scll + 7) / iclk;
+	 * scll + 7 = iclk / 2 * speed
+	 * sclh + 5 = iclk / 2 * speed
+	 */
+	scll = sclh = iclk / (2 * speed);
+	scll -= 7;
+	sclh -= 5;
+	if ((scll < 0) || (sclh < 0)) {
+		printf("Error : I2C initializing clock\n");
+		return;
+	}
 
 	writew(0x2, I2C_SYSC); /* for ES2 after soft reset */
 	udelay(1000);
@@ -42,12 +84,10 @@ void i2c_init (int speed, int slaveadd)
 		udelay (50000);
 	}
 
-	/* 12MHz I2C module clock */
-	writew (0, I2C_PSC);
-	speed = speed/1000;		    /* 100 or 400 */
-	scl = ((12000/(speed*2)) - 7);	/* use 7 when PSC = 0 */
-	writew (scl, I2C_SCLL);
-	writew (scl, I2C_SCLH);
+	writew(psc, I2C_PSC);
+	writew(scll, I2C_SCLL);
+	writew(sclh, I2C_SCLH);
+
 	/* own address */
 	writew (slaveadd, I2C_OA);
 	writew (I2C_CON_EN, I2C_CON);
diff --git a/include/asm-arm/arch-omap3/i2c.h b/include/asm-arm/arch-omap3/i2c.h
index 3937f35..09afca0 100644
--- a/include/asm-arm/arch-omap3/i2c.h
+++ b/include/asm-arm/arch-omap3/i2c.h
@@ -112,14 +112,14 @@
 #define I2C_SCLH_HSSCLH		8
 #define I2C_SCLH_HSSCLH_M	0xFF
 
-#define OMAP_I2C_STANDARD	100
-#define OMAP_I2C_FAST_MODE	400
-#define OMAP_I2C_HIGH_SPEED	3400
-
-#define SYSTEM_CLOCK_12		12000
-#define SYSTEM_CLOCK_13		13000
-#define SYSTEM_CLOCK_192	19200
-#define SYSTEM_CLOCK_96		96000
+#define OMAP_I2C_STANDARD	100000
+#define OMAP_I2C_FAST_MODE	400000
+#define OMAP_I2C_HIGH_SPEED	3400000
+
+#define SYSTEM_CLOCK_12		12000000
+#define SYSTEM_CLOCK_13		13000000
+#define SYSTEM_CLOCK_192	19200000
+#define SYSTEM_CLOCK_96		96000000
 
 #define I2C_IP_CLK		SYSTEM_CLOCK_96
 #define I2C_PSC_MAX		0x0f
-- 
1.6.0.5