diff options
Diffstat (limited to 'drivers/i2c')
| -rw-r--r-- | drivers/i2c/mxs_i2c.c | 87 |
1 files changed, 34 insertions, 53 deletions
diff --git a/drivers/i2c/mxs_i2c.c b/drivers/i2c/mxs_i2c.c index 73a6659..b907f7b 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> @@ -213,62 +214,39 @@ 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); + /* + * The timing derivation algorithm. There is no documentation for this + * algorithm available, it was derived by using the scope and fiddling + * with constants until the result observed on the scope was good enough + * for 20kHz, 50kHz, 100kHz, 200kHz, 300kHz and 400kHz. It should be + * possible to assume the algorithm works for other frequencies as well. + * + * Note it was necessary to cap the frequency on both ends as it's not + * possible to configure completely arbitrary frequency for the I2C bus + * clock. + */ + uint32_t clk = mxc_get_clock(MXC_XTAL_CLK); + uint32_t base = ((clk / 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 (!spd) { - printf("MXS I2C: Invalid speed selected (%d Hz)\n", speed); + 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), @@ -280,12 +258,15 @@ 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 clk = mxc_get_clock(MXC_XTAL_CLK); + 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); + /* + * This is a reverse version of the algorithm presented in + * i2c_set_bus_speed(). Please refer there for details. + */ + return clk / ((((timing0 >> 16) - 3) * 2) + 38); } void i2c_init(int speed, int slaveadd) |