linux-kernel - Re: [PATCH v3 01/11] stm class: Introduce an abstraction for System Trace Module devices

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Date:	Thu, 30 Jul 2015 15:11:13 +0800
From:	Chunyan Zhang <zhang.lyra@...il.com>
To:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Mathieu Poirier <mathieu.poirier@...aro.org>,
	peter.lachner@...el.com, norbert.schulz@...el.com,
	keven.boell@...el.com, yann.fouassier@...el.com,
	laurent.fert@...el.com,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
	Chunyan Zhang <zhang.chunyan@...aro.org>,
	Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH v3 01/11] stm class: Introduce an abstraction for System
 Trace Module devices

On Thu, Jul 30, 2015 at 2:59 PM, Chunyan Zhang <zhang.lyra@...il.com> wrote:
> On Thu, Jul 30, 2015 at 2:37 PM, Alexander Shishkin
> <alexander.shishkin@...ux.intel.com> wrote:
>> Chunyan Zhang <zhang.lyra@...il.com> writes:
>>
>>> Sure, I mean, the root reason of this problem is here ( i.e.
>>> "stm_core_up" was zero then):
>>>      if (!stm_core_up)
>>>          return -EPROBE_DEFER;
>>>
>>> Why it was zero?
>>> Because the function (i.e. stm_core_init() ) in which "stm_core_up"
>>> would be added one hasn't been executed at this moment. It would be
>>> executed on module_init stage for you this version of patch.
>>
>> Again, this is the indented behavior.
>>
>>> The reason of this warning is:
>>> After stm_probe() failed, clk_core_disable() would be called from
>>> amba_put_disable_pclk(), then WARN_ON() happened:
>>>          if (WARN_ON(core->enable_count == 0))
>>>                  return;
>>>
>>> I'm guessing the reason why "core->enable_count" was 0 at this moment is:
>>> I don't know who created a thread to process the
>>> amba_pm_runtime_suspend(), in which clk_core_disable() was already
>>> called, "core->enable_count" was, of course, cleared to zero then.
>>> And this thread run before amba_put_disable_pclk(pcdev) which is just
>>> the one called from amba_probe() after
>>> "->probe"(i.e. stm_probe in this case) returning a non-zero value.
>>
>> No, this is guesswork. In amba_probe(), clocks are enabled for the
>> drv->probe() and then disabled afterwards and that's where the refcount
>> ends up unbalanced, the probe is the culprit.
>>
>> I can debug your driver for you but you'll at least need to put the code
>> up somewhere so I can see it.
>
> The code has already been submitted like I said in the earlier emails,
> you may refer [1].
>
> Thanks,
> Chunyan
>
> [1] https://lkml.org/lkml/2015/2/4/729

Er, sorry, it's too old, I'll send out an updated version soon.

Thanks for your patience,
Chunyan

>
>>
>> Regards,
>> --
>> Alex
>>
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