Re: [PATCH] ARM: dts: Remove mau_pd node for Exynos5420

[Tomasz Figa <tomasz.figa@gmail.com>]

On 24.04.2014 13:03, Tushar Behera wrote:
> On 04/24/2014 03:36 PM, Tomasz Figa wrote:
>> On 24.04.2014 11:07, Tushar Behera wrote:
>>> On 04/23/2014 03:43 PM, Kukjin Kim wrote:
>>>> Tushar Behera wrote:
>>>>>
>>>>> On 22 April 2014 13:08, Alim Akhtar <alim.akhtar@gmail.com> wrote:
>>>>>> Hi Tushar
>>>>>>
>>>>>> On Tue, Apr 22, 2014 at 11:09 AM, Tushar Behera
>>>>>> <tushar.behera@linaro.org> wrote:
>>>>>>> MAU powerdomain provides clocks for Audio sub-system block. This
>>>>>>> block
>>>>>>> comprises of the I2S audio controller, audio DMA blocks and Audio
>>>>>>> sub-system clock registers.
>>>>>>>
>>>>>>> Right now, there is no way to hook up power-domains with clock
>>>>> providers.
>>>>>>> During late boot when this power-domain gets disabled, we get
>>>>>>> following
>>>>>>> external abort.
>>>>
>>>> + Jonghwan Choi
>>>>
>>>> Well, this is not a perfect solution to support MAU power domain,
>>>> it's true it is a problem right now though.
>>>>
>>>> In other words, this is just temporal fix for the problem.
>>>>
>>>> How about accessing clock stuff for audio sub-system with handling
>>>> MAU power domain via generic IO power domain?
>>>>
>>>
>>> + Tomasz Figa
>>>
>>> Existing power domain driver exynos4_pm_init_power_domain is registered
>>> with an arch_initcall whereas the clk-exynos-audss driver is registered
>>> with core_initcall. Hence even if add mau_pd node to clk-exynos-audss
>>> node, the binding with power-domain doesn't happen.
>>
>> I'd say core_initcall is way too early for clk-exynos-audss driver. It
>> should be at most subsys_initcall. As far as I can see, all users of
>> clocks provided by this driver (i.e. i2s) are probed at device_initcall
>> level anyway.
>>
>
> It is also used by ADMA node, which gets probed.

If I'm looking correctly, ADMA is handled by pl330 driver which is 
registered at device_initcall level and so it shouldn't make problems 
with clk-exynos-audss driver being probed at subsys_initcall level.

>
>>>
>>> Alternately, if Tomasz's patches are applied [1], power-domain binding
>>> is successful. But because of the init order, clk-exynos-audss defers
>>> probe resulting in a kernel crash. Forcing clk-exynos-audss to register
>>> through arch_initcall() fixes this issue, but I am not sure if that is
>>> okay.
>>
>> If the driver crashes on deferred probe, then it's a bug and it should
>> be fixed.
>>
>
> By the time clk-exynos-audss is getting called, mau_pd is already
> disabled by power-domain driver. That is not getting enabled during
> clk-exynos-audss probe. Am I missing something?

Probably. The driver should enable runtime PM and call 
pm_runtime_get_sync() to make sure that power is supplied to the device 
it accesses.

By the way, if defining MAU power domain in DT, then also all the 
devices inside of this domain should be bound to it, including ADMA and 
I2S, but I don't see neither of them having the "samsung,power-domain" 
property.

Best regards,
Tomasz