[PATCH RFC] i2c: rk3x: handle dynamic clock rate changes correctly

[addy ke]

Hi Max

On 2014/9/13 19:26, Max Schwarz wrote:
> Hello Addy,
> 
> On Wednesday 10 September 2014 at 16:16:10, Addy wrote:
>>> @@ -724,16 +816,28 @@ static int rk3x_i2c_probe(struct platform_device
>>> *pdev)
>>>
>>>        return ret;
>>>    
>>>    }
>>>
>>> +    i2c->clk_rate_nb.notifier_call = rk3x_i2c_clk_notifier_cb;
>>> +    ret = clk_notifier_register(i2c->clk, &i2c->clk_rate_nb);
>>> +    if (ret != 0) {
>>> +        dev_err(&pdev->dev, "Unable to register clock notifier\n");
>>> +        goto err_clk;
>>> +    }
>>> +
>>> +    i2c->clk_freq = clk_get_rate(i2c->clk);
>>> +    rk3x_i2c_set_scl_rate(i2c, i2c->scl_frequency);
>>
>> I have tested on rk3288-pinky board:
>> I2c clock must be enabled before driver call rk3x_i2c_set_scl_rate()
>> to write div value to CLKDIV register. If not, system will crash.
>>
>> So we need call clk_enable() before rk3x_i2c_set_scl_rate().
> 
> Interesting. It works without problems on RK3188. Do you know if the clock has 
> to be kept enabled for some time? Or is it okay to do it like this?
> 
> clk_enable(i2c->clk);
> rk3x_i2c_set_scl_rate(i2c, i2c->scl_frequency);
> clk_disable(i2c->clk);
>
> Cheers,
>   Max
>
Before write value to i2c register, it is necessary to enable i2c's clock and parent clock!

In the linux-rockchip branch code, the i2c's clock and parent clock are enabled by default.
So there are no problems on it.

But on rk388-pinky board, pclk_peri is disabled when i2c driver is probed.
(Maybe its reference count drops to 0 and it is disabled by clk driver)

Hi, Doug
Do you known why pclk_peri is disabled when i2c driver is probed?
My test branch is cros/chromeos-3.14.


> 
>