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

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Date:	Wed, 1 Jun 2016 16:01:31 +0200
From:	"M'boumba Cedric Madianga" <cedric.madianga@...il.com>
To:	Maxime Coquelin <mcoquelin.stm32@...il.com>
Cc:	Patrice Chotard <patrice.chotard@...com>,
	Wolfram Sang <wsa@...-dreams.de>,
	Rob Herring <robh+dt@...nel.org>,
	Russell King <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-i2c@...r.kernel.org
Subject: Re: [PATCH 2/5] i2c: Add STM32F4 I2C driver

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