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

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Message-ID: <CAAfSe-vBnqC4QNMXLK2H2b8XUAiXz5qk8BO90Y=a5azfqWe+nw@mail.gmail.com>
Date:	Thu, 30 Jul 2015 14:59:14 +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 2:37 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

>
> Regards,
> --
> Alex
>
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