Re: [PATCH v5 1/6] clk: hisilicon: add CRG driver for hi3519 soc

[Rob Herring <robh+dt@kernel.org>]

On Fri, Jan 15, 2016 at 1:57 AM, xuejiancheng <xuejiancheng@huawei.com> wrote:
>
> On 2016/1/14 21:16, xuejiancheng wrote:
>> Hi Mike,
>>
>> On 2016/1/14 2:57, Michael Turquette wrote:
>>> Quoting xuejiancheng (2016-01-12 19:03:01)
>>>> Hi Stephen,
>>>>    Thank you very much for your reply.
>>>>
>>>> On 2016/1/13 6:12, Stephen Boyd wrote:
>>>>> On 01/08, Jiancheng Xue wrote:
>>>>>> diff --git a/drivers/clk/hisilicon/Kconfig b/drivers/clk/hisilicon/Kconfig
>>>>>> index e434854..b6baebf 100644
>>>>>> --- a/drivers/clk/hisilicon/Kconfig
>>>>>> +++ b/drivers/clk/hisilicon/Kconfig
>>>>>> @@ -1,3 +1,10 @@
>>>>>> +config COMMON_CLK_HI3519
>>>>>> +    tristate "Clock Driver for Hi3519"
>>>>>
>>>>> It looks like this has to be bool. Otherwise it needs to be a
>>>>> platform driver and the hisilicon APIs need to be exported and
>>>>> lose their __init markings.
>>>>>
>>>> Yes,it's a problem. I will fix it in next version. Thank you.
>>>
>>> The best solution would be to make this clock driver a real platform
>>> driver.
>>>
>> Now the work clock of the clocksource timer-sp804 is provided by this driver. So
>> it need to be registered early by CLK_OF_DECLARE. If the timer clock is treated
>> as a fixed-clock provider, this driver can be implemented as a platform driver.
>> Then the crg device must be registered before other clock consumer devices.Accordingly
>> the crg device node must be written above all other clock consumer devices node in dts files.
>> I think it is also a dependence.
>>
>> Can you help me understand why it is better to make this driver a platform driver?
>> Thank you very much!
>>
> arch_initcall(customize_machine)
> -->of_platform_populate
>    -->of_platform_bus_create
>      -->of_amba_device_create
>         -->amba_device_add
>            -->amba_get_enable_pclk
> The call sequence above shows that the clock of the amba device must be registered before
> amba_device_add. The clock of "arm,pl011" uart is registered in the probe function of the
> platform driver "hi3519-crg". So the platform device "hi3519-crg" must be created before
> the amba device "arm,pl011" uart.

It is a problem, but Tomeu had a fix to support deferred probes here.
That was part of the on-demand probing series, but maybe it needs to
be applied separately if we are moving clock drivers to platform
drivers.

Rob