Re: [PATCH 2/5] i2c: Add STM32F4 I2C driver

From	"M'boumba Cedric Madianga" <cedric.madianga@gmail.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 2/5] i2c: Add STM32F4 I2C driver
Date	2016-06-01 16:10 +0200
Message-ID	<rFf0l-Xx-13@gated-at.bofh.it> (permalink)
References	<rxEoV-2BM-3@gated-at.bofh.it> <rxEoW-2BM-21@gated-at.bofh.it> <rzJNw-2Rf-23@gated-at.bofh.it> <rA45A-7no-9@gated-at.bofh.it>
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Hi Maxime,

>>> +static void stm32f4_i2c_set_speed_mode(struct stm32f4_i2c_dev *i2c_dev)
>>> +{
>>> +       struct stm32f4_i2c_timings *t = &i2c_timings[i2c_dev->speed];
>>> +       u32 ccr, val, clk_rate;
>>> +
>>> +       ccr = readl_relaxed(i2c_dev->base + STM32F4_I2C_CCR);
>>> +       ccr &= ~(STM32F4_I2C_CCR_FS | STM32F4_I2C_CCR_DUTY |
>>> +                STM32F4_I2C_CCR_CCR_MASK);
>>> +
>>> +       clk_rate = clk_get_rate(i2c_dev->clk);
>>> +
>>> +       switch (i2c_dev->speed) {
>>> +       case STM32F4_I2C_SPEED_STANDARD:
>>> +               val = clk_rate / t->rate * 2;
>>> +               if (val < STM32F4_I2C_MIN_CCR)
>>> +                       ccr |= STM32F4_I2C_CCR_CCR(STM32F4_I2C_MIN_CCR);
>>> +               else
>>> +                       ccr |= STM32F4_I2C_CCR_CCR(val);
>>> +               break;
>>> +       case STM32F4_I2C_SPEED_FAST:
>>> +               ccr |= STM32F4_I2C_CCR_FS;
>>> +               if (t->duty) {
>>> +                       ccr |= STM32F4_I2C_CCR_DUTY;
>>> +                       ccr |= STM32F4_I2C_CCR_CCR(clk_rate / t->rate * 25);
>>> +               } else {
>>> +                       ccr |= STM32F4_I2C_CCR_CCR(clk_rate / t->rate * 3);
>>> +               }
>> Is it really useful since duty seems to always be 0?
> Agree, I will rework it by directly set duty at 0 in the register.

Contrary to what I wrote previously, the duty has to be set for FAST
Mode to reach 400khz.
So, I am going to keep the timing struct and set duty to 1 for FAST mode

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Re: [PATCH 2/5] i2c: Add STM32F4 I2C driver "M'boumba Cedric Madianga" <cedric.madianga@gmail.com> - 2016-06-01 16:10 +0200
  Re: [PATCH 2/5] i2c: Add STM32F4 I2C driver Maxime Coquelin <mcoquelin.stm32@gmail.com> - 2016-06-01 16:20 +0200
    Re: [PATCH 2/5] i2c: Add STM32F4 I2C driver "M'boumba Cedric Madianga" <cedric.madianga@gmail.com> - 2016-06-02 17:40 +0200
      Re: [PATCH 2/5] i2c: Add STM32F4 I2C driver Maxime Coquelin <mcoquelin.stm32@gmail.com> - 2016-06-02 18:10 +0200
        Re: [PATCH 2/5] i2c: Add STM32F4 I2C driver "M'boumba Cedric Madianga" <cedric.madianga@gmail.com> - 2016-06-03 09:50 +0200

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