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authorMike Frysinger <vapier@gentoo.org>2009-10-14 19:27:27 -0400
committerHeiko Schocher <hs@denx.de>2009-10-30 15:10:58 +0100
commit08a1c6258c2a04cead33eac50d96ea89979dcb94 (patch)
tree13417f423897c2c72c257e4416fa5d03b020915d /drivers/i2c
parent3814ea4f0002536ac592480b2cdafa319a16e329 (diff)
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Blackfin: TWI/I2C: implement bus speed get/set functions
While we're here, improve the speed calculation a bit to match the HRM. Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Diffstat (limited to 'drivers/i2c')
-rw-r--r--drivers/i2c/bfin-twi_i2c.c59
1 files changed, 48 insertions, 11 deletions
diff --git a/drivers/i2c/bfin-twi_i2c.c b/drivers/i2c/bfin-twi_i2c.c
index 5ef30be..73a78d2 100644
--- a/drivers/i2c/bfin-twi_i2c.c
+++ b/drivers/i2c/bfin-twi_i2c.c
@@ -26,6 +26,7 @@
#ifdef TWI0_CLKDIV
#define bfin_write_TWI_CLKDIV(val) bfin_write_TWI0_CLKDIV(val)
+#define bfin_read_TWI_CLKDIV(val) bfin_read_TWI0_CLKDIV(val)
#define bfin_write_TWI_CONTROL(val) bfin_write_TWI0_CONTROL(val)
#define bfin_read_TWI_CONTROL(val) bfin_read_TWI0_CONTROL(val)
#define bfin_write_TWI_MASTER_ADDR(val) bfin_write_TWI0_MASTER_ADDR(val)
@@ -44,8 +45,21 @@
#ifdef CONFIG_TWICLK_KHZ
# error do not define CONFIG_TWICLK_KHZ ... use CONFIG_SYS_I2C_SPEED
#endif
-#if CONFIG_SYS_I2C_SPEED > 400000
-# error The Blackfin I2C hardware can only operate at 400KHz max
+
+/*
+ * The way speed is changed into duty often results in integer truncation
+ * with 50% duty, so we'll force rounding up to the next duty by adding 1
+ * to the max. In practice this will get us a speed of something like
+ * 385 KHz. The other limit is easy to handle as it is only 8 bits.
+ */
+#define I2C_SPEED_MAX 400000
+#define I2C_SPEED_TO_DUTY(speed) (5000000 / (speed))
+#define I2C_DUTY_MAX (I2C_SPEED_TO_DUTY(I2C_SPEED_MAX) + 1)
+#define I2C_DUTY_MIN 0xff /* 8 bit limited */
+#define SYS_I2C_DUTY I2C_SPEED_TO_DUTY(CONFIG_SYS_I2C_SPEED)
+/* Note: duty is inverse of speed, so the comparisons below are correct */
+#if SYS_I2C_DUTY < I2C_DUTY_MAX || SYS_I2C_DUTY > I2C_DUTY_MIN
+# error "The Blackfin I2C hardware can only operate 20KHz - 400KHz"
#endif
/* All transfers are described by this data structure */
@@ -213,7 +227,36 @@ static int i2c_transfer(uchar chip, uint addr, int alen, uchar *buffer, int len,
return ret;
}
-/*
+/**
+ * i2c_set_bus_speed - set i2c bus speed
+ * @speed: bus speed (in HZ)
+ */
+int i2c_set_bus_speed(unsigned int speed)
+{
+ u16 clkdiv = I2C_SPEED_TO_DUTY(speed);
+
+ /* Set TWI interface clock */
+ if (clkdiv < I2C_DUTY_MAX || clkdiv > I2C_DUTY_MIN)
+ return -1;
+ bfin_write_TWI_CLKDIV((clkdiv << 8) | (clkdiv & 0xff));
+
+ /* Don't turn it on */
+ bfin_write_TWI_MASTER_CTL(speed > 100000 ? FAST : 0);
+
+ return 0;
+}
+
+/**
+ * i2c_get_bus_speed - get i2c bus speed
+ * @speed: bus speed (in HZ)
+ */
+unsigned int i2c_get_bus_speed(void)
+{
+ /* 10 MHz / (2 * CLKDIV) -> 5 MHz / CLKDIV */
+ return 5000000 / (bfin_read_TWI_CLKDIV() & 0xff);
+}
+
+/**
* i2c_init - initialize the i2c bus
* @speed: bus speed (in HZ)
* @slaveaddr: address of device in slave mode (0 - not slave)
@@ -229,15 +272,9 @@ void i2c_init(int speed, int slaveaddr)
bfin_write_TWI_CONTROL(prescale);
/* Set TWI interface clock as specified */
- bfin_write_TWI_CLKDIV(
- ((5 * 1024 / (speed / 1000)) << 8) |
- ((5 * 1024 / (speed / 1000)) & 0xFF)
- );
-
- /* Don't turn it on */
- bfin_write_TWI_MASTER_CTL(speed > 100000 ? FAST : 0);
+ i2c_set_bus_speed(speed);
- /* But enable it */
+ /* Enable it */
bfin_write_TWI_CONTROL(TWI_ENA | prescale);
SSYNC();