Re: [U-Boot] [PATCH v2] mxs: i2c: Implement algorithm to set up arbitrary i2c speed

Hello Marek,

On 30.11.2012 16:28, Marek Vasut wrote:

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 in datasheet. When using the values from the datasheet, the I2C clock were completely wrong.

Signed-off-by: Marek Vasutmarex@denx.de Cc: Stefano Babicsbabic@denx.de Cc: Fabio Estevamfabio.estevam@freescale.com Cc: Wolfgang Denkwd@denx.de

---

arch/arm/cpu/arm926ejs/mxs/clock.c | 2 + arch/arm/include/asm/arch-mxs/clock.h | 1 + drivers/i2c/mxs_i2c.c | 75 ++++++++++----------------------- 3 files changed, 26 insertions(+), 52 deletions(-)

v2: Properly implement XTAL clock retrieval. The i2c clock are derived from the 24MHz XTAL clock.

[...]

diff --git a/drivers/i2c/mxs_i2c.c b/drivers/i2c/mxs_i2c.c index 006fb91..b040535 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); }

This change is not described in the patch description, please fix.

void mxs_i2c_setup_read(uint8_t chip, int len) @@ -210,62 +214,29 @@ int i2c_probe(uchar chip) return ret; }

-static struct mxs_i2c_speed_table {

[...]

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 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;

a lot of magic constants ...

• 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);

^ ^ spaces

writel((0x0030<< I2C_TIMING2_BUS_FREE_OFFSET) | (0x0030<< I2C_TIMING2_LEADIN_COUNT_OFFSET), @@ -277,12 +248,12 @@ 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);

• return clk / ((((timing0>> 16) - 3) * 2) + 38);

^ spaces

... and here a lot of magic constants too ... as this is a result of measuring ... we should at least note here, that we have this values from a scope session and the values in the manual seem to be not correct ...

Hmm... I am a little confused ... you write the i2c_regs->hw_i2c_timing{0,1,2} registers in i2c_set_bus_speed() but you return in i2c_get_bus_speed() just results from reading the i2c_regs->hw_i2c_timing0 register only and do some funny calculations ... is this correct?

}

void i2c_init(int speed, int slaveadd)

Thanks!

bye, Heiko