Re: [PATCH] i2c: designware: Do not require clock when SSCN and FFCN are provided

[Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>]

On 12/16/2015 08:28 AM, Mika Westerberg wrote:
> On Wed, Dec 16, 2015 at 08:11:12AM -0600, Suravee Suthikulpanit wrote:
>>> The clk framework should work fine if the returned clock is NULL (which
>>> I think is your case).
>>>
>>> The driver gates clocks when the device is suspended and on Intel LPSS
>>> there actually is a clock that gets gated.
>>>
>>>> [..]
>>>> @@ -203,13 +223,11 @@ static int dw_i2c_plat_probe(struct platform_device *pdev)
>>>>   		dev->master_cfg =  DW_IC_CON_MASTER | DW_IC_CON_SLAVE_DISABLE |
>>>>   			DW_IC_CON_RESTART_EN | DW_IC_CON_SPEED_FAST;
>>>>
>>>> -	dev->clk = devm_clk_get(&pdev->dev, NULL);
>>>> -	dev->get_clk_rate_khz = i2c_dw_get_clk_rate_khz;
>>>> -	if (IS_ERR(dev->clk))
>>>> -		return PTR_ERR(dev->clk);
>>
>> Actually, if we don't provide the clock (which is the case for ACPI), this
>> would also return and cause the probing to fail.
>
> Indeed it seems that when you have CONFIG_COMMON_CLK selected the clock
> framework starts returning errors if the clock is not found.
>
> Since we need the clock for Intel LPSS I2C host controllers (and they
> may have *CNT methods), I think you just need to provide the clock for
> AMD I2C host controller in similar way than we do in
> drivers/acpi/acpi_lpss.c.

I am trying to avoid having to hard-coded clock frequency value in the 
driver. Would it be alright to not return w/ error, and just do the 
following?

	dev->clk = devm_clk_get(&pdev->dev, NULL);
	if (!IS_ERR(dev->clk))
		dev->get_clk_rate_khz = i2c_dw_get_clk_rate_khz;

This should work for the Intel case when clock is also provided.

Thanks,
Suravee