Re: [PATCH v11 10/27] iommu/exynos: use managed device helper functions

[Tomasz Figa <t.figa@samsung.com>]

On 19.03.2014 10:01, Sachin Kamat wrote:
> On 19 March 2014 14:29, Cho KyongHo <pullip.cho@samsung.com> wrote:
>> On Tue, 18 Mar 2014 16:14:53 +0100, Tomasz Figa wrote:
>>> On 18.03.2014 12:09, Cho KyongHo wrote:
>>>> On Fri, 14 Mar 2014 20:52:43 +0530, Sachin Kamat wrote:
>>>>> Hi KyongHo,
>>>>>
>>>>> On 14 March 2014 10:35, Cho KyongHo <pullip.cho@samsung.com> wrote:
>>>>>> This patch uses managed device helper functions in the probe().
>>>>>>
>>>>>> Signed-off-by: Cho KyongHo <pullip.cho@samsung.com>
>>>>>> ---
>>>>> [snip]
>>>>>
>>>>>> +       data->clk = devm_clk_get(dev, "sysmmu");
>>>>>> +       if (IS_ERR(data->clk)) {
>>>>>> +               dev_info(dev, "No gate clock found!\n");
>>>>>> +               data->clk = NULL;
>>>>>> +       }
>>>>>
>>>>> Why aren't you returning from here upon error?
>>>>
>>>> It is for the case of a System MMU which does not need clock gating.
>>>>
>>>
>>> Are there really such cases?
>>>
>>
>> Yes.
>> Especially in the case of initial stage of new SoC development.
>>
>> I have experianced some software workaround for H/W restriction
>> needs prevention of clock gating for some devices.
>
> So aren't these basically some exceptions/hacks rather than the usual way
> of functioning of the device?
>

This actually raises a good question, whether we really need to support 
such early development SoC versions in mainline.

Another thing is that if you need to assure that a clock is ungated, you 
must acquire it and prepare_enable explicitly, so I don't think this 
kind of handling is correct.

Best regards,
Tomasz